A Simple Counter Application in PLC

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The programmable controller includes both down counters and up counters . The up counter counts from zero up to the preset count where some action takes place.

PLC Counter Example

PLC Counter Example

The down counter goes from a preset number down to zero where the action occurs. A conveyor motor diagram is shown in Figure illustrating the application of an up-counter.

The counter counts the number of cases coming off the conveyor. When the total number of cases reaches 10, the conveyor motor stops automatically.

A proximity switch is used to sense the passage of cases.

A Simple Counter Application 

A Simple Counter Application in PLC

The sequential task is as follows:

1. The START button is pressed to start the conveyor motor.

2. Cases move past proximity switch and increment the counter’s accumulated value.

3. After a count of 10, the conveyor motor stops automatically and the counter’s accumulated value is reset to zero with SP2.

4. The conveyor motor can be stopped manually without loss of the accumulated count.

5. The accumulated count of the counter can be reset by means of the COUNTER RESET button.

Author: Dr. Hadi Saadat

  • Relay Ladder Logic
  • NO and NC Contacts
  • PLC Logic Warning Signal
  • Motor Starter Control
  • Limit Switch PLC Logic

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perfect , good detailed explanation

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Using PLC Timers and Counters: Advanced Programming Techniques

Introduction.

PLC timers and counters are essential tools in industrial automation programming. They enable precise control of time-based events and accurate counting of processes. This tutorial-style article explores advanced techniques for utilizing timers and counters in PLC programming. It covers topics such as cascading timers, preset values, retentive vs. non-retentive timers/counters, and provides application-specific examples to illustrate their practical usage.

Understanding PLC Timers

Basic timer operation.

PLC timers allow programmers to create time-based delays, schedules, or event triggers. A timer typically has an input, an output, and a preset value. When the input is activated, the timer starts counting from zero towards the preset value. Once the timer reaches the preset value, the output is activated, indicating that the desired time delay has elapsed. Timers are commonly used in applications such as motor control, process sequencing, and event synchronization.

Retentive vs. Non-Retentive Timers

PLC timers can be retentive or non-retentive. A retentive timer retains its accumulated value even when power is lost or the PLC is restarted. This is useful for applications where it’s important to maintain timing accuracy across power cycles. On the other hand, non-retentive timers reset to zero when power is lost, requiring them to be reactivated or reset upon power restoration. The choice between retentive and non-retentive timers depends on the specific application requirements.

Cascading Timers

Cascading timers involve connecting multiple timers in series to create more complex timing sequences. By linking timers together, programmers can achieve multi-step or multi-stage operations. Each timer in the cascade is triggered by the completion of the previous timer in the sequence. Cascading timers provide flexibility in designing intricate time-based processes without the need for additional programming logic. They are commonly used in applications such as synchronized machine operations, batch processing, and conveyor control systems.

Exploring PLC Counters

Basic counter operation.

PLC counters are used to count events, pulses, or cycles in a process. A counter typically has an input, an output, and a current value. When the input is activated, the counter increments its value by one. Once the counter reaches a specified count, the output is activated, indicating that the desired number of events or cycles has been reached. Counters are widely used in applications such as production line monitoring, inventory control, and quality assurance.

Preset Values

Counters often have a preset value that determines when the output is activated. The preset value represents the target count that the counter should reach before triggering the output. Programmers can set the preset value based on the desired number of events or cycles to be counted. Using preset values allows for precise control over the process and enables automatic triggering of subsequent actions.

Count Up vs. Count Down

PLC counters can count up or count down depending on the application requirements. Counting up involves incrementing the counter’s value with each input activation, while counting down involves decrementing the value. Counting up is commonly used when monitoring the number of items produced, while counting down is useful for tracking remaining time or inventory quantities. The choice between count up and count down counters depends on the specific application context.

Advanced Timer and Counter Techniques

Using timers and counters in combination.

Combining timers and counters can lead to more advanced and versatile programming techniques. For instance, timers can be used to control the duration of counter operations or to introduce delays between count increments. This combination allows for precise control over timed events and flexible counting operations. By leveraging the interaction between timers and counters, programmers can create complex and highly customizable automation sequences.

Application-Specific Examples

To better understand the practical usage of advanced timer and counter techniques, let’s explore some application-specific examples:

Bottling Line Control : In a bottling line, timers can be used to control the interval between bottle placements, while counters can keep track of the number of bottles filled. By combining timers and counters, the system can ensure a consistent flow of bottles with accurate counting.

Conveyor System Synchronization : In a conveyor system, cascading timers can be employed to synchronize the movement of multiple conveyors. By setting up a sequence of timers, each conveyor can start and stop at specific intervals, enabling smooth and coordinated material handling.

Batch Processing : In batch processing applications, timers can be utilized to control the duration of each processing step, while counters keep track of the number of completed batches. This ensures precise timing for each step and accurate batch counting for quality control purposes.

Motor Control : Timers and counters play a crucial role in motor control applications. Timers can be used to control the motor’s start/stop duration, while counters monitor the number of rotations or cycles performed by the motor. This information can be utilized for maintenance scheduling or performance analysis.

These examples highlight the versatility and power of advanced timer and counter techniques in PLC programming. By applying these techniques, programmers can design robust and efficient automation systems tailored to specific industrial requirements.

Best Practices

When working with PLC timers and counters, it’s essential to follow best practices to ensure reliable and maintainable code. Here are some recommended practices:

Proper Naming and Documentation

Provide clear and descriptive names for timers, counters, and associated variables. This improves code readability and makes it easier for other programmers to understand and maintain the code. Additionally, document the purpose, functionality, and usage of each timer and counter in the program documentation for future reference.

Error Handling

Implement proper error handling mechanisms to handle exceptional conditions. For example, if a timer fails to complete within the expected time, it’s important to handle the timeout condition and take appropriate actions. Robust error handling ensures the system can recover gracefully from unexpected situations and prevents potential safety hazards or process failures.

Testing and Validation

Thoroughly test and validate the functionality of timers and counters during the development phase. Perform unit testing to verify individual timer and counter operations. Additionally, conduct integration testing to ensure they work correctly within the overall system. Continuous validation and monitoring of timers and counters are crucial to maintain system reliability and accuracy.

PLC timers and counters are powerful tools for precise time-based control and accurate event counting in industrial automation. By understanding advanced techniques such as cascading timers, preset values, retentive vs. non-retentive timers/counters, and combining timers and counters, programmers can create highly efficient and flexible automation systems. The application-specific examples provided demonstrate the practical usage of these techniques in various industrial scenarios. By following best practices and conducting thorough testing, programmers can ensure reliable and maintainable PLC programs that meet specific industrial requirements.

Further Reading

Troubleshooting plc systems: common issues and solutions.

Introduction PLC (Programmable Logic Controller) systems play a crucial role in industrial automation, providing control and monitoring capabilities for various processes. However, like any comple...

Instrumentation Basics: Understanding Sensors, Transmitters, and Actuators

1. Introduction Instrumentation plays a crucial role in industrial automation by providing accurate measurement and control of various process parameters. This article serves as a foundational ove...

Key Components of Industrial Instrumentation

Introduction Industrial instrumentation plays a vital role in monitoring and controlling various processes in industrial settings. It involves the use of specialized components and technologies to...

PLC Programming Standards and Documentation Best Practices

Advanced PLC Programming Techniques and Best Practices

PLC Timers and Counters, their types and Practical Uses

Table of Contents

Description:

PLC Timers and Counters

  PLC Timers and Counters, their types and Practical Uses- In this article, I am only going to talk about the PLC Timers and counters, this article can be a bit longer as I will be sharing with you the ladder logic diagrams, which will explain the practical uses of PLC Timers and Counters. I am pretty sure you know the importance of Timers and Counters and that’s the reason you are reading this article.

PLC Timers and Counters are frequently used in industries for time delays and production monitoring. There are situations when you need to turn OFF a certain machine after some time, or you need to turn ON a machine after a certain delay when a sensor is activated or a button is pressed. You might have seen a lot of videos on YouTube in which the Bottles, Boxes, etc on a conveyor belt are counted. I hope this article will help you to learn the basics so that you can develop some advanced level monitoring and control systems using the PLC Timers and Counters. Without any further delay let’s get started!!!

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What is a Timer?

An automatic mechanism for activating or deactivating a device at a preset time. Let me explain this. A timer is the modified version of a Clock used for measuring specific time intervals.

Timers have mainly two types

  • A Timer which can count from Zero to a certain pre-defined value, which type of the Timer is also known as the Stopwatch.
  • Another type of device which counts down from a specified time interval is more usually called a Timer.

Timers can be classified into two main categories,

Hardware Timers:

            Mechanical timers

            Electromechanical timers

            Electronic timers

Software Timers

            Software applications

            Other types

All the above timers are used only for one purpose which is Time.

Timers in PLC “Fatek”:

PLC Timers and Counters

If you look at the Timer Function Block and Operand are given above. You can clearly see the Time control EN “enable” this an input signal from a button, or Sensor, it has two Operands Tn which is the Timer Number and the Operand PV which is the Preset value of the timer.

In Fatek PLC the total number of timers is 255 (T0 ~ T255) with three different time resolutions or bases, 0.01S, 0.1S, and 1S. These timers with different time resolutions can be used as per the requirement.

Timers and time bases:

T0 ~ T49: 0.01S timer (default as 0.00 ~ 327.67S)

T50 ~ T199: 0.1S timer (default as 0.0 ~ 3276.7S)

T200~T255: 1S timer (default as 0 ~ 32767S)

Timers Time can be calculated using the following formula.

Time = time base X Pre-set value.

Lets, for example, we want to make a 5 seconds delay using the T0 timer which has the time base .01s.

Time = .01 X 500

While using the T0 time we will need to select a pre-set value of 500.

Now let’s do the same using the Timer T50 which has the time base .1S

Timer Time = .1 X 50

Timer Time = 5S

PLC Timer Practical use Example1:

Ladder Logic program for a Conveyor belt.

Write a program that starts the Conveyor Belt after 5 Seconds when a button is pressed. Use a light/buzzer as the indicator. After the Conveyor Belt starts then turn OFF the light. Use timer T50. The button is connected with the X0 input of the PLC. The bulb is connected with the Y0 output and the Conveyor Belt Motor is connected with the output Y1.

Sounds complicated?

Well, at first it looks so complicated, but in PLC Ladder Logic programming this is very simple, I mean very simple. Let’s do.

Open the WinProLadder software.

Note: If you don’t know how to use the WinProLadder software then read my previous articles and then you can resume from here.After you open the WinProLadder Software.

PLC Timers and Counters

Enter Project information. Select a project name, select the Model, write any description if you want and then click on the ok button. Write the following Ladder Logic Program. I hope you know how to use different contacts if not then read my previous articles.

Let me tell you how to add a timer,

PLC Timers and Counters

Click the F key on the keyboard write T as the function name and press the OK button. The following function block will be opened.

PLC Timers and Counters

Simply enter the time number which you want to use let’s say T50 and a pre-set value of 50.

Time = .1 X 50 = 5 seconds delay. This is how you can add a timer. Now let’s continue with our example.

PLC Timers and Counters

This is a very simple yet very powerful program that is most frequently used in industries.

When the Button/Switch connected with the X0 input of the Fatek PLC is pressed the timer T50 is started and meanwhile the bulb indicator connected with the Y0 output is turned ON. When the timer T50 reaches the pre-set value the bulb indicator is turned OFF and the conveyor belt Motor is Turned ON. This Motor will remain ON until we turn OFF the button/switch connected with the input X0.

This program is really amazing, explains two activities, the bulb remains ON for 5 seconds and then Turns OFF and the Conveyor belts Start after a delay of 5 seconds. Now it totally depends on your logic how you use this small piece of code in advanced level projects.

Traffic Light Controller using PLC Timers:

PLC Timers and Counters

No matter we are learning Arduino or 8051 family microcontrollers, as a beginner, we always wish to make traffic control system. In this small project, I am going to write a very simple traffic light control system. I will turn ON each light for 5 seconds and then it repeats forever unless you turn OFF the switch. Let’s start with the Circuit diagram.

Three lights RED, YELLOW, and GREEN are connected with outputs Y0, Y1, and Y2. One switch is connected with X0 to activate and deactivate the traffic control system. Now let’s have a look at the ladder logic diagram of the PLC-based traffic control system.

PLC Timers and Counters

While the switch X0 is turned ON all the lights RED, YELLOW, and GREEN are turned on one by one. This cycle is repeated infinite times until and unless the switch is turned OFF.

I hope, now you have a basic understanding of how to use different timers.

What is a Counter?

In very simple words, a counter is a device which is used for counting anything, you can count pulses, you can count events, you can count physical objects, etc. Unlike the Timers, Counters are also most frequently used in industrial processes where you need to monitor the production.

Counters in PLC “FATEK”:

PLC Timers and Counters

In the above picture, you can clearly see the Function Block and the operands. The Clock CK and the Clear control CLR are the control signals and Cn is the Counter number while the PV is the Preset value. Each time a signal is detected at the clock input the counter is incremented. When a signal is detected at the Clear control input the counter value is reset back to zero. The CUP which is the counter up flag remains low until the counter values reach the Preset value and then the CUP flag gets high.

In Fatek PLC the total number of counters is (C0 ~ C255).

There are a total of 200 16-bit counters (C0 ~ C199). The range of the Preset value can be between 0 ~ 32767. C0 ~ C139 are Retentive Counters and the CV value will be retained when the PLC turns ON or RUN after a power failure or a PLC STOP. For Non-Retentive Counters, if a power failure or PLC STOP occurs, the CV value will be reset to 0 when the PLC turns ON or RUN again.

There are total of 56 32-Bit counters (C200~C255). The range of the Preset value is between 0~2147483647. C200~C239 are Retentive Counters and C240~C255 are Non-Retentive Counters.

To insure the proper counting, the sustain time of the input status of CLK should greater than 1 scan time.

The max counting frequency with this instruction can only up to 20Hz, for higher frequency please use the high-speed soft/hardware counter

When “CLR” is at 1, all of the contact Cn, FO0 (CUP), and CV value of the counter CV are cleared to 0 and the counter stops counting.

When “CLR” is at 0, the counter is allowed to count up. The Counter counts up every time the clock “CK” changes from 0 to 1 (adds 1 to the CV) until the cumulative current value is equal to or greater than the Preset value (CV>=PV), the counter “Count-Up” and the contact status of the counter Cn and FO0 (CUP) changes to 1. If the input status of the clock continues to change, even the cumulative current value is equal and greater than the Preset value; the CV value will still accumulate until it reaches the up limit at 32767 or 2147483647. The contact Cn and FO0 (CUP) stay at 1 as long as CV>=PV unless the “CLR” input is set to 1.

PLC Counter Practical use Example2:

PLC Timers and Counters

This is a very basic button clicks counting system. Each time the button1 is press it increments the value. When the value is reached the Preset value which is 4 the bulb will turn ON. As you can see in the picture below.

PLC Timers and Counters

To reset the value you can simply click on the clr button.

PLC Timer and Counter together Practical Example 3:

Now we are going to write a program which can count the seconds. We can use a one-second pulse M1922. The Preset value is 20. It means when the 20 seconds are completed the bulb connected with the output Y0 will be turned ON. You can reset the counter by pressing the clr button.

PLC Timers and Counters

So with this, my article on PLC timers and counters comes to an end. I will be uploading some advanced level projects using timers and counters. Make sure you subscribe to my website and follow my Facebook page.

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chapter 6 programming plc timers and counters

Chapter 6 Programming PLC Timers and Counters

Sep 28, 2014

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Chapter 6 Programming PLC Timers and Counters.

  • timer instructions
  • delay timers
  • ctd instructions
  • ctu instructions count
  • retentive timers begin timing

morrison

Presentation Transcript

Chapter 6Programming PLC Timers and Counters Timer and Counter Instructions • Timer Instructions • Timer Instruction Words • Timer On-Delay (TON) Instructions • Timer Off-Delay (TOF) Instructions • Retentive Timer (RTO) Instructions • Reset (RES) Instructions • Special Applications • Counter Instructions • Counter Instruction Words • Count Up (CTU) Instructions • Count Down (CTD) Instructions

PLCs provide a cost-effective alternative to using individual hardwired timers and counters because the smallest PLCs (nanos and micros) already contain 10 or more timers and counters.

Timer instructions contain three words, with word “0” containing three bits that can be used in the program of a PLC.

Timers following on-delay (TON) instructions begin timing when the logic preceding the instruction on a rung changes from false to true.

A PLC with a programmed timer using timer on-delay (TON) instructions can be used to replace hardwired on-delay timers.

Timers following off-delay (TOF) instructions start timing when the logic preceding the instruction on a rung changes from true to false.

Off-delay timers are used in applications that require a load to remain energized after the input has been removed.

Retentive timers begin timing when the logic preceding the instruction on a rung changes from false to true. Retentive timers retain their accumulated value until reset.

Free running timers are continuously timing because the XIO instruction preceding the timer is always true.

Timers are cascaded by having the DN bit of timer #0 activate timer #1. The only limit to the number of cascaded timers is the size of the memory in the PLC.

Cascaded timers are used to start equipment sequentially, such as when starting three conveyors with a 10 sec delay between the start of each conveyor.

Counter instructions contain three words. The bits and words of counter instructions have addresses that can be used in the program of a PLC.

Count up (CTU) instructions increase the accumulated value incrementally on each false to true transition of the logic preceding the instruction.

Counters are used in applications that require items or products to be counted.

A CTD instruction counts down on every false to true transition of the logic preceding the instruction and shares the same status bits, preset values, and accumulated values as the corresponding CTU instruction.

CTU and CTD instructions can be used to keep track of the cars entering and exiting a parking lot.

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Counters in PLC Programming

PLC Counters

A PLC counter is a function block that counts up or down until it reaches a limit. When the limit is reached the output is set.

The thing is that counting is in fact widely used in PLC programming. Often you will have the need to counts different things. An example of this could be to keep track of how many times a process has been completed. Or how many products has been produced.

PLC counters are also used to assist logging to SCADA systems by counting the amount of times these events has happened or setting alarms when an event has happened a certain amount of times.

With all that said timers are very useful and it is crucial for every PLC programmer to know the basics of counting in a PLC program. In this article I will explain how counters work, and how you can use them in your PLC programs.

You can either watch my video tutorial about PLC counters or read it here just below the video:

Basics of Counting in a PLC Counter Limits High-Speed Counters Counter Function Blocks Up Counter (CTU) Down Counter (CTD) Up Down Counter (CTUD)

Basics of Counting in a PLC

Before you start counting in any PLC program there are some basics you should know first. These are basic information about the counter instructions and the PLC itself.

First of all, it is important to know about the limits of counting in a PLC.

Counter Limits

Counters use variables of certain data types to store numbers in the PLC. All counters need to store at least two numbers:

  • Counter Limit
  • Current Counter Value

Since these two numbers are saved in a certain data type they also have their limits. Many PLC’s save these two numbers as WORD or Integer data types and if you remember the basics of PLC data types, you will know that a WORD takes up 16 bits.

A signed integer also takes up 16 bits, but the first one is used for signing, so you will only have 15 bits for the actual number

With a little bit of calculation we’ll quickly find out that the maximum value of a WORD is 16.535 . The maximum value of the signed integer is 32.767 .

Although it is rare that you will need to count to such high numbers, it is still important know to avoid overflow errors.

High-Speed Counters

Sometimes the frequency of the pulse you’re trying to count is just too high. This often happens with encoders and other high speed components. In this case you will need a special input module for high frequency (speed) signals.

These input modules are better known as high-speed counters and they are built to capture inputs of various high frequencies.

Counter Function Blocks

All counter operations or counter function blocks has some inputs and some outputs. In fact, I talked about two of them before (counter limit and current counter value).

What is important to know here is which data type the inputs and outputs take. Normally for counters this is boolean and WORD data types, but it can depend on the PLC platform you’re using. So, don’t forget to check the documentation for the counter on the PLC platform you’re using.

Up Counter (CTU)

The first counter instruction I will introduce you to is the up counter, also known as just CTU. As the name implies, this PLC counter is used for counting up.

You can see the up counter function block illustrated below:

Up Counter (CTU) Function Block

The way is works is that it will set an output, when is has counted a certain amount of times. To be a little more specific this is how it works.

How it works

Each pulse on the count input (CU) will increase the current counter value (CV) by 1. When CV is greater than or equal to the counter limit (PV) the output (Q) is set. A pulse on the reset input (R) will reset the value of CV to 0.

Up counters are usually used to keep track of how many times an event has happened. Let’s say you want a process to complete 10 times before cleaning needs to happen.

For this you have to set the counter limit (PV) to 10. Each time the process has completed you will give a pulse on the count input (CU). When the process has completed 10 times, the output (Q) will be set. Now you can use that output to for example set an alarm that the system needs cleaning.

When cleaning is done you can give a pulse on the reset input (R) and you can now start over again.

Down Counter (CTD)

Counting down is another operation that is widely used in PLC programming. In some cases you want to know how many counts are remaining before the limit is reached. With the up counter you can use some math to do it. But you can do it easily with a down counter.

Because with the down counter you will count down from a certain number until it reaches 0.

Down Counter (CTD) Function Block

As you can see the down counter has a pin called LD instead of the reset. It is called load and is used for loading a value into the current counter value. Because when you count down to 0 you will need some initial value of the counter.

Each pulse on the count input (CD) will decrement current counter value (CV) by 1. When CV is less than or equal to 0 the output (Q) is set. A pulse on the load input (LD) will assign the value of counter limit (PV) to CV.

Imagine you have a semi-automatic process where the operator needs to do a manual task to start a process. The process need to be completed 10 times but when there is 2 times left the operator needs to inspect. It is important that the operator can see how many processes are left, since the total amount of processes can vary.

This is where the down counter comes in handy. What you need to do here is to assign the total amount of process times to the counter limit (PV) and then give at pulse at the load input (LD). Now you have to total amount as the current counter value (CV).

Every time the process has completed you give a pulse on the count input (CD). You can now use CV to show the operator how many processes are left. When he can see that there are 2 left, he needs to inspect. Additionally you can even add an alarm by comparing CV to 2 with an equality operator .

Up Down Counter (CTUD)

At last you have the up down counter which can count both ways. Sometimes the combination of the up and the down counter can be useful. You can count the same number both up and down and set both an upper and a lower limit.

As you can see below it has a bit more pins than the two other counters:

Up Down Counter CTUD Function Block

The whole idea about this counter is that it can count both up and down the same current counter value (CV). At the top of the function block you can see that there are 2 count inputs. One for counting up and one for counting down.

Each pulse on the count input (CU) will increase the current counter value (CV) by 1. And each pulse on the count input (CD) will decrement current counter value (CV) by 1. When CV is greater than or equal to the counter limit (PV) the output (QU) is set. When CV is less than or equal to 0 the output (QD) is set. A pulse on the reset input (R) will reset the value of CV to 0. A pulse on the load input (LD) will assign the value of counter limit (PV) to CV.

One way of using the up down counter is to count finished products. Say you want to produce a certain amount of products in a batch control system. But after every product is finished a manual inspection is needed. If a product is discarded you will have to subtract it from the number of finished products.

For this you can use the up down counter. Every time a product is finished you can give a pulse at the count up input (CU). But if at inspection the product fails the quality test you can give a pulse at the count down input (CD) to decrement the amount of products produced.

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PLC Counter Programming for Beginners

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In this article, I will be talking about PLC counter. I will explain what PLC counters are, how they work, the different types of counters, and give some examples of how they are used.

PLC counters are internal PLC instructions that can be used to count input or output signals in the PLC program . These counters operate like relay counters but you cannot hold a PLC counter in your hand and they do not need to be connected to wires to operate.

PLC Counters.

Types of PLC counters

There are two main types of PLC counters, the count-up counter, and the count-down counter.

For the counter-up counters, we have a counter file name, a counter preset value, a counter accumulated value, a counter count-up bit, and a counter done bit.

For the counter-down counters, we have the same bits and values. The only thing that is different is the counter-down bit on the output. As you can see below, we have this as counter-up bit for the counter-up counter.

PLC counter tags

There are also two internal memory bits of counter overflow and counter underflow which we’ll discuss later in this article.

PLC counter values

The counter file name is a PLC tag. This tag is where you can find the counters preset and accumulated values and the counters count-up, count-down, done, overflow, and underflow bits.

PLC counter tags

Some PLCs create the counter file name for you, and other PLCs have you create the counter file name.

For example, RSLogix 500 creates the counter file name for you but when using Studio 5000, you need to create the counter file name.

PLC counter file name

For all of my counter examples, I will use the counter file name Counter1. I will also use a momentary push-button to trigger the counters.

PLC counter example

For all of my PLC counter examples, I will be using Studio 5000, which is the PLC programming software for Allen Bradley ControlLogix PLCs. But the things that you will learn here in these examples, can be applied to any other PLC software. Because the overall counter functions are similar to any other PLC brand.

Studio 5000 PLC counter

Count-up counter

For the first example, I will talk about the count-up counter. I will start by adding a count-up counter instruction to a PLC program rung.

Count-up counter instruction

I will also add the momentary push-button input to this rung to trigger the counter.

Momentary push-button input

I’ll type Counter1 for the counter name, and type five into the preset value to finish setting up this counter.

Count-up counter

Next, I will download this program to the PLC emulator.

If you need any help with downloading the program, there are plenty of videos that show you how to do that. Just give YouTube a good search and you can easily find those videos.

Ok, before I push the button, the counter’s accumulated value is equal to zero.

When I push and hold the button, the count-up bit turns on, and the accumulated value changes to one.

Count-up counter values

When I release the button, the count-up bit turns off but the accumulated value stays at one. So every time I push the button, the count-up bit turns on, and the accumulated value increases by one.

Notice the accumulated value of my counter is now four. At this point when I push the button, the count-up bit turns on, the done bit turns on, and the accumulated value changes to five.

Count-up counter done bit

If I continue to push and release the button, the count-up bit will still turn on while the button is pushed, the done bit will stay on, and the accumulated value will still increase.

Count-up counter accumulated value increasing

Counter reset bit

To reset the counter back to zero and turn off the done bit, I will have to add a counter reset bit to the PLC program and add another momentary push-button input to trigger the reset bit.

Count-up counter reset

Now let’s say we have a workstation and we need to know how many parts are built at this workstation. A counter can be set up to count when a part gets released in auto from this workstation.

If only a certain number of parts need to be built, the done bit can be used to let the operator know when they are done.

Count-down counter

I will now add a count-down counter to my PLC program and another momentary push-button input to trigger this counter. I will type Counter1 as the counter’s name and yes this is the same name as the count-up counter.

Count-down counter

Count-up and count-down counters work together, when they have the same name they share the preset and accumulated values, and they share the done bit.

Again I will push and hold the button to trigger the count-up counter. Notice the count-up counter acts the same as it did before the count-down counter was added, but the accumulated value of both counters increases to one.

Counter count-up

When the accumulated value is four and the count-up counter is triggered, the done bits on both counters will be on.

Count-up and count-down counter Done

At this point, when I push and hold the button to trigger the count-down counter, the count-down bit turns on, both done bits turn off, and the accumulated value of both counters decreases to four.

Counter count-down

Counter negative direction

If I keep pushing and releasing the count-down button after the accumulated value reaches zero, it will start to count in the negative direction.

Counter negative direction

A count-up and a count-down counter can be used to count bad parts that need to get removed and reworked. When the parts get removed the accumulated value increases. When the parts get reworked and get put back with the good parts, the accumulated value decreases.

Counter overflow and underflow bits

Now let’s talk about the overflow and underflow bits. The overflow bit is used on count-up counters and the underflow bit is used on count-down counters.

Counter underflow bit

Counter overflow

When a count-up counter is at its maximum accumulated value and then gets triggered to count up, the overflow bit will turn on.

Counter negative direction

Counter underflow

When a count-down counter is at its maximum negative accumulated value and then gets triggered to count down, the underflow bit will turn on.

Counter underflow bit.

Maximum accumulated value

The numbers that some of these counters will have to reach for the overflow or the underflow bits to turn on are very large. For example, I am using a ControlLogix PLC for my counter examples.

The counters in ControlLogix PLCs have a maximum positive accumulated value of more than 2 billion and they have a maximum negative accumulated value greater than -2 billion.

That means the counters for these PLCs can count up or count down over 2 billion times before their accumulated value will overflow or underflow.

These are the exact positive and negative accumulated values for these counters when using a ControlLogix PLC if you like to know that.

maximum positive accumulated value < 2,147,483,647

maximum negative accumulated value > -2,147,483,648

Maximum accumulated value

These minimum and maximum number values are not the same for all PLC brands. So double-check the minimum and maximum preset values of your PLCs counters before adding one to your program.

In review, by reading this article you have learned about the two main types of PLC counters, the count-up counter, and the count-down counter.

That these counters have a preset value, an accumulated value, a count-up bit, a count-down bit, a counter done bit, an overflow bit, and the underflow bit.

You have also learned some examples of where these counters are used.

Please let us know if you have any questions about the two main types of PLC counters in the comments below.

Got a friend, client, or colleague who could use some of this information? Please share this article.

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Chapter 6 Programming PLC Timers and Counters

Page 1: Chapter 6 Programming PLC Timers  and Counters

PowerPoint® Presentation

Chapter 6Programming PLC Timers

and Counters

Timer and Counter Instructions • Timer Instructions • Timer Instruction Words • Timer On-Delay (TON) Instructions • Timer Off-Delay (TOF) Instructions • Retentive Timer (RTO) Instructions • Reset (RES)

Instructions • Special Applications • Counter Instructions • Counter Instruction Words • Count Up (CTU) Instructions • Count Down (CTD) Instructions

Page 2: Chapter 6 Programming PLC Timers  and Counters

Chapter 6 — Programming PLC Timers and Counters

PLCs provide a cost-effective alternative to using individual hardwired timers and counters because the smallest PLCs (nanos and micros) already contain 10 or more timers and counters.

Page 3: Chapter 6 Programming PLC Timers  and Counters

Timer instructions contain three words, with word “0” containing three bits that can be used in the program of a PLC.

Page 4: Chapter 6 Programming PLC Timers  and Counters

Timers following on-delay (TON) instructions begin timing when the logic preceding the instruction on a rung changes from false to true.

Page 5: Chapter 6 Programming PLC Timers  and Counters

A PLC with a programmed timer using timer on-delay (TON) instructions can be used to replace hardwired on-delay timers.

Page 6: Chapter 6 Programming PLC Timers  and Counters

Timers following off-delay (TOF) instructions start timing when the logic preceding the instruction on a rung changes from true to false.

Page 7: Chapter 6 Programming PLC Timers  and Counters

Off-delay timers are used in applications that require a load to remain energized after the input has been removed.

Page 8: Chapter 6 Programming PLC Timers  and Counters

Retentive timers begin timing when the logic preceding the instruction on a rung changes from false to true. Retentive timers retain their accumulated value until reset.

Page 9: Chapter 6 Programming PLC Timers  and Counters

Free running timers are continuously timing because the XIO instruction preceding the timer is always true.

Page 10: Chapter 6 Programming PLC Timers  and Counters

Timers are cascaded by having the DN bit of timer #0 activate timer #1. The only limit to the number of cascaded timers is the size of the memory in the PLC.

Page 11: Chapter 6 Programming PLC Timers  and Counters

Cascaded timers are used to start equipment sequentially, such as when starting three conveyors with a 10 sec delay between the start of each conveyor.

Page 12: Chapter 6 Programming PLC Timers  and Counters

Counter instructions contain three words. The bits and words of counter instructions have addresses that can be used in the program of a PLC.

Page 13: Chapter 6 Programming PLC Timers  and Counters

Count up (CTU) instructions increase the accumulated value incrementally on each false to true transition of the logic preceding the instruction.

Page 14: Chapter 6 Programming PLC Timers  and Counters

Counters are used in applications that require items or products to be counted.

Page 15: Chapter 6 Programming PLC Timers  and Counters

A CTD instruction counts down on every false to true transition of the logic preceding the instruction and shares the same status bits, preset values, and accumulated values as the corresponding CTU instruction.

Page 16: Chapter 6 Programming PLC Timers  and Counters

CTU and CTD instructions can be used to keep track of the cars entering and exiting a parking lot.

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Timers. PLC timers are output instruction that provides the same function as mechanical timing relay. PLC timers are output instruction that provides.

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PLC Counter | How counters work in PLC? | Basic Guidance

PLC Counter

Hey Friends! How are you? I hope you like the tutorial of PLC instructions.

We have seen Bit logic instructions , Arithmetic and Comparator instructions , PLC timer instructions , PLC programming languages in my previous tutorial.

In this blog, we are going to see about the PLC counter instructions with practical PLC counter instructions programming examples.

Table of Contents

PLC Counter | What is a counter in PLC?

A PLC Counter is a function in PLC programming that is used to measure things like how many times an event has happened in a process or how many times a product has been produced.

In this blog, we are going to see how plc counters work? and how can we use counters in the PLC program?

Siemens PLC Counter Block:

In Siemens PLC we have three types of counter functions,

  • Down Counter
  • Up and Down Counter

PLC Counter

These are the blocks that are used as a counter in PLC ladder logic. All counter blocks have some inputs and some outputs.

  • CU – Count Up Input
  • CD – Count Down Input
  • S – Set Input for presetting counter
  • PV – Value for presetting counter
  • R – Reset Input
  • Q – Status of Counter
  • CV – Current counter value
  • CV_BCD – Current counter value in BCD coded

Up Counter(S_CU)

PLC Counter

For each pulse at Count Up(CU) bit, the current Counter Value(CV) will be increased by 1. When there is a pulse at Set input(S), it will set Presetting Value(PV) at the current Counter Value(CV).

When there is a pulse at Reset input(R), the counter block will get reset and the current counter value is set at 0 again.

There is an indicating alarm when the production limit reaches 100.

Down Counter(S_CD)

PLC Counter

There is an alarm showing that the production limit has reached below 10.

Up Down Counter(S_CUD)

PLC Counter

At each pulse at Count Up(CU) bit, it will increase the current Counter Value(CV), and each pulse at Count Down(CD) bit, will decrease the current Counter Value(CV).

When there is a pulse at the Set input(S), it will set Presetting Value(PV) at the current Counter Value(CV).

When there is a pulse at Reset input(R), the counter block will get reset and the current Counter value is set at 0 again.

Suppose there is a limit of 50 vehicles in a parking lot. So it will show the vacant positions and parking full indicator.

Allen Bradley PLC Counter Block:

In Allen Bradley PLC we have three types of counter functions,

PLC Counter

The inputs and outputs of these counter blocks have some inputs and outputs.

  • Preset – Value for presetting counter
  • Accum – Current counter value

Counter Up(CTU)

This instruction is used to count up the value. Whenever there is a pulse at the input of the CTU block, it will increase the accumulator value by 1. 

When the accumulator value is equal to or greater than the preset value, the DN bit is set. The DN bit is true until the accumulator value goes below the preset value or CTU is reset using RES instruction.

Counter Down(CTD)

This instruction is used to count down the value. Whenever there is a pulse at the input of the CTD block, it will decrease the accumulator value by 1. 

When the accumulator value is equal to or greater than the preset value, the DN bit is set. The DN bit is true until the accumulator value goes below the preset value.

PLC Counter Applications:

  • Bottle Filling Plant
  • Parking Space Application
  • Sequential Controller Application

Summary(PLC Counter Instructions)

This is all the information about the counter function in PLC programming. I hope you like this blog, if you want more tutorial about PLC programming then please comment down below.

Next Must-Read Articles:

⇒ What is PLC? How does it work?

⇒ Sinking and Sourcing Circuits.

⇒ Logic Gates using PLC Ladder logic.

⇒ 5 different types of PLC programming languages.

⇒ Electrical motor starter with a PLC program.

⇒ 20+ Arithmetic instructions in PLC Programming.

⇒ Basics of PLC Timer in PLC System.

⇒ Different Types of Siemens PLC Programming blocks.

⇒ 30+ Most useful PLC Communication Protocols.

⇒ Converter instructions in PLC Programming.

⇒ Analog Scaling and Unscaling in PLC Programming.

⇒ Difference between FC and FB in Siemens PLC.

⇒ What is memory in Siemens PLC?

⇒ Top PLC Manufacturers: PLC Brands and Ranking.

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by Dipali Chaudhari

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Basics of PLC Timer | Types of PLC Timer & Applications

Everybody knows why time is so important in our life. Whether it is human or machine, nothing can be done without time.

Every little thing around us is getting automated. Here we are interested in PLC ( Programmable Logic Controller ) automation.

In PLC automation, different types of PLC programming instructions are used with their different specifications.

Out of these PLC ladder diagram (LD) programming instructions, timer instruction is one of the most important instructions which plays a very significant role.

In this tutorial, I am describing the PLC timer in detail with the programming instructions and functions.

Let’s start from the beginning.

Table of Contents

What is the PLC Timer?

PLC timer is a instruction to control and operate the device for a specific duration. With the timer, we can perform any specific operations for a particular time span.

A timer is one of the most essential and useful entity.

You can set time-based activity with the help of the PLC programming timer instruction. Every PLC having different timer functions.

The timer instruction is used to provide programming logic and to decide when to turn on or off the circuit.  It has both normally open (NO) or normally closed (NC) contact.

Let’s see here, the representation of the input and output timer NO and NC contact in LD programming.

give a presentation on real time plc counter applications

Timer output contact is shown in the coil form or box form or rectangular form. In AB and Siemens PLC, it is represented in the box shape.

If you want to perform work or device activity in a particular time span, you have to get familiar with the timers. For this, you have to learn I/O timer instructions for writing the PLC program.

In the Ladder Diagram (LD) PLC programming, you can set the PLC timer from millisecond (ms) to an hour (hr) time range.

Are you interested in knowing, how does it actually work?

Let’s see the internal circuit of the timer.

Basic Internal Circuit of PLC Timer

Now, we are looking at the internal timer circuit of the PLC. The working of the timer circuit is based on the four main parts.

Each of the Internal parts of the timer circuit has various features and functions. This is how they are connected and constructed in the given diagram.

timer block diagram in plc timer

Here are some of the basic terminologies you need to understand about timer used in the PLC.

1. Input and Output Modules

The module which interacts with the input signal is called as Input Module . Input module requires to connect to the timer circuit for providing the input signal.

The module which interacts with the output signal is called as Output Module . The output module is required to connect the timer circuit.

Read More: PLC Input Module and Output Module

2. Power Supply Module

The power module provides a power supply for the proper functioning of the timer circuit. It can connect with the ac voltage source (like 120, 230 V AC) or dc voltage source (like 5,12, 24 V DC).

3. Internal Timer Circuit

The timer circuit performs the set and resets functions.

If the auxiliary power supply is ‘on’, the timer will give the momentary input pulse for the set and reset operation.

4. Timer Digital Display

The digital timer displays the set and elapsed timing value.

For the automation purpose, the values can be displayed in a few milliseconds (ms). This will be easy for tracking your automation system.

What are the types of the PLC Timer?

For the ladder diagram programming, the classification of the PLC programming timer is-

1. On Delay Timer (TON)

An on-delay timer (TON) is a programming instruction which use to start momentary pulses for a set period of time.

Let’s see, a simple construction of the AB PLC On-delay timer programming instruction.

on delay plc timer

2. Off Delay Timer (TOFF)

A off-delay (TOF) timer is a PLC programming instruction which use to switch off the output or system after a certain amount of time.

See here, a basic structure of AB PLC Off delay timer programming instruction.

off delay PLC timer

3. Retentive On/Off Timer (RTO)

The main function of the RTO is used to  hold  or  store  the set (accumulated) time.

RTO is used in the case when there is a change in the rung state, power loss, or any interruption in the system.

In the AB PLC, retentive timer instruction look like this.

retentive timer on off rto plc timer

You can briefly read about the each types of PLC timer with an example .

 Timer Instructions Address for Multiple PLC Brands

We have seen three timers provide the time delay functions to control the PLC operations. There are four main values that timer deals with.

  • Timer Address
  • Preset Value
  • Timer Base Value
  • Accumulated value

Each timer instruction has three very useful status bits. These bits are…

  • Enable bit (EN)
  • Timer Timing bit (TT)
  • Done Bit (DN).

In the AB and Siemens PLC, the output bit is often called the timer’s ‘Done bit’. And it indicates the timer has reached its preset time.

1. Addressing for ABB PLC

In the ABB PLC programming, we can simply write the I/O timer address of the ladder diagram. We can set the timer value in ranges from ‘ T0 ‘ to ‘ T255 ‘.

You can see the above diagram of the I/O contact representation.

2. Addressing for AB (Rockwell) PLC

For the AB PLC, the timer has the address ranging from ‘ T4:0′ upto ‘ T4:255 ‘.

Where, T4 is the file type.

Addressing format for timer instruction with the three status bits.

  • Enable bit (EN) address is ranging from ‘T4:0/EN’ upto ‘T4:255/EN’.
  • The addressing for Timer timing bit (TT) is ranging from ‘T4:0/TT’ upto ‘T4:255/TT’.
  • Done bit (DN) address is ranging from ‘T4:0/DN’ upto ‘T4:255/DN’.

3. Addressing for Siemens PLC

In the Siemens, LD program can be written with the five types of timers.

  • Pulse timer (S_Pulse)
  • Pulse extended timer (S_PExT)
  • On delay timer (S_ODT)
  • On delay extended timer (S_ODTS)
  • Off delay timer (S_OffDT)

The general block diagram of the timer (In Siemens PLC),

give a presentation on real time plc counter applications

S – Set value or signal for the timer

TV – Time Variable. It is used to store time value in the form of

You can enter the time value from 1 to 9990 seconds.

R- Reset value of the timer

Q – Output of the timer

BI – Current time in binary code

BCD – Current time in binary decimal code

4. Addressing for Delta PLC

For the WPLSoft software (Delta PLC), you can use timer addressing ranging from ‘ T0′ to ‘ T127 ‘.

In Delta PLC, input timer address is shown like general representation (T0, T1,…….. T127). And Output coil is written in the form of

‘T0’ is timer address and ‘K’ is the constant term

Delta PLC timer block diagram:

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For Delta PLC, the timer starts for a 10-second.  It should be written in the form of ‘T0 K100’.

5. Addressing for Mitsubishi PLC

Both, Mitsubishi PLC and Delta PLC, use the same timer addressing format.

Example-based on the PLC Timer Instruction

The very basic and real-life example is controlling traffic signals using PLC automation .

After a certain (fixed) time, each side signal has to turn on and off. At a time only one side traffic signal should be on.

This logic can be implemented using simple PLC timers.

What are the Applications of Timer Instruction?

Here are some of the basics applications of timer you can use in a PLC automation environment.

  • Use for the delay action
  • It is used to run or stop operation as per the user’s command.
  • The RTO timer helps to record or hold an intermediate time value.

This is all about PLC timer. This is a really big topic. I tried to make it simple. If you have any questions, feel free to ask in the comment.

If you are new to the PLC programming, I have shared my thought about how you can master and learn PLC for free .

And if you are ready to give PLC online test, here is a  PLC Automation Quiz .

give a presentation on real time plc counter applications

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Dipali Chaudhari

I have completed master in Electrical Power System. I work and write technical tutorials on the PLC, MATLAB programming, and Electrical on DipsLab.com portal.

Sharing my knowledge on this blog makes me happy.  And sometimes I delve in Python programming.

39 thoughts on “Basics of PLC Timer | Types of PLC Timer & Applications”

Best one…you do great one & your site also very helpful to learn new think easily.

Thanks for visiting my site.

Can u tell software for plc programming?

If you are new for the learning PLC, I guess using those free version of any PLC software brand is sufficient for your need.

You can download Delta PLC software from its official website for free.

I have explained the details in the following link- https://dipslab.com/how-to-learn-plc-programming-free/

RS Logix (AB PLC) and Step 7- Simatic Manager (Simens PLC) are the best software for PLC.

And also, I have shared the 12 brands of PLC with their software. https://dipslab.com/different-plc-software-brands/

Very nice explanation madam

Thanks, Akbar:)

Very good for learning.

Thanks, Vijay Sharma.

All time favorite blog for plc.

Thanks,Punit.

Thank you, Kunal Shah

Good work mam.

Thank you, Manavarthi.

Excellent, Its a wonderful apart from others.

Thank you, Lavkush:)

Hi, Thank you for your services. It’s really useful. I hope you will share more posts.

Surely, I will publish more tutorials related to PLC.

So many thanks for your time explanation, please continue some more knowledge share.

From- Thi Win, Myanmar.

Thanks, you too for reaching out to my blog.

And I am promising that, I will share more tutorials for DipsLab Reader like you. 🙂

This is an informative article and it’s very useful and knowledgeable.

Thanks, Sumit 🙂

Good explanation, Dipali.

Thanks, Gopal 🙂

Thanks, Mam to share information regarding the PLC timer.

You are welcome, Dear 🙂

Very informative

Thanks, Rajesh.

For any process, delay timers used in PLC programming. Three types of timers are found- On delay, Off delay, and retentive timer.

In Siemens PLC, we have ODT, ODTS, PULSE TIMER, PULSE RETENTIVE, OFF DELAY TIMER.

Right, each timer has different specifications for Siemens PLC.

Great. Usually, we don’t have many number of timers in plcs when we used of ladder diagrams as programming language. I can say- On delay, and Off dealy.

working with codesys myself I would say this was a bit helpful.

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Instrumentation and Control Engineering

PLC Counter Instruction

Counter

Preset counters

Mechanical counters, electronic counters, how does a plc counter compare to a timer, what are some of the benefits of using a counter in a plc, instruction for coil-formatted counter, types of counter, features of up and down counter, what is negative counter, up & down counters are basic types of plc. it is further it is classified as, counter counting sequence up counter, counter counting sequence down counter, allen bradely’s plc counter, feature of plc counter, plc-5 and slc 500 count-up and down counter, controllogix count-up counter instruction, rs logic counter, cascading counters for extremely large counts, 1. parts counting program, 2. in-process monitoring system, 3. parking garage counter program.

         Typical applications of counters include keeping track of the number of items going through a particular point and determining the number of times a particular activity is carried out.

         When the counted total of a preset counter matches the user-entered preset restrictions, the counter is able to regulate an external circuit.

Preset counters

         It is possible for programmable counters to perform the same purposes as mechanical counters.

Mechanical Counters

  • The counter increases by one number whenever the actuating lever is moved over it, and the actuating lever always goes back to its starting position when it is no longer in use.
  • A pushbutton on the side of the machine is used to reset everything to its default value of zero.

         Electronic counters have the ability to count up, count down, or combine the two functions to count both up and down. They must rely on external sources in order to perform counting tasks, such as components moving in front of a sensor or activating a limit switch .

         Similar to timers, PLC counter instructions rely on external or program sources rather than an internal clock to perform their counting functions.

  • A PLC counter can use a sensor and hence function as a no-contact counter is one of the many advantages of employing this counting method. The possibility that light parts will be unable to move the mechanical counting operator.
  •  PLC counters typically have retention.

         When the accumulated count equals the preset count, the output is energized and the counter output is closed. The counter contact can be used as many times as you wish throughout the program as an NO or NC contact.

Instruction of Coil-Formatted Counter

  • The typical counter starts counting at zero and continues until it reaches the intended value, also known as the PRESET value.
  • The current value, also known as the accumulated count, is the total that has been accumulated.
  • Counters can count up, count down, or combine the two to count both up and down at the same time.
  • Most the counters that are utilized in industry are up-counters, but various applications demand the introduction of down-counters or combination up/down counters. Counters are mainly used in tracking the moving items to a particular point
  • Up Counters : Up counters begin counting from a starting value, and when a predetermined count value is reached, an output signal is produced.
  • Down Counters: Down counters count down from a starting value, and when a predetermined count value is achieved, an output signal is produced.

Up & Down Counter

  • Counter file name, counter preset value, counter accumulated value, counter count-up bit, and counter done bit for the counter-up counters.
  • We have the same bits and values for the counters that are lower in the stack.
  • The output’s counter-down bit is the only item that has changed.

         The negative counter means after the total amount reaches zero, the count-down button will begin to count backwards when pressed and released.

What is meant by counter overflow and underflow bits?

         For count-up counters and count-down counters, respectively, the overflow bit and the underflow bit are used.

  • Overflow Bits – The overflow bit is activated when a count-up counter reaches its maximum accumulated value and is then triggered to count up.
  • Underflow Bits – The underflow bit is activated when a count-down counter reaches its maximum negative cumulative value and is then triggered to begin counting down.
  • Up/Down Counter
  • Ring counter
  • Event Counter
  • Batch Counter
  • Up/Down Counters: Depending on which way the input signal is going, these counters can count either up or down. They are frequently employed in situations where the procedure can go either way.
  • Shift Register Counters: Shift register counters of the type called “ring counters” forward the output signal to the following stage after each count. They are utilized in applications where it is necessary to count a series of events.
  • Event Counters: Event counters are used to keep track of how frequently a particular process event occurs, such as how frequently a button is pressed.
  • Batch counters: Used in applications where a specified amount needs to be generated, batch counters are used to count a specific number of events or activities.

Counter Counting Sequence

  • PLC counters typically have a memory.
  • On processor restart, the counter will contain the same count that it did at the moment of processor shutdown.
  • However, if the reset condition is engaged at the moment of power restoration, the counter can be reset.

PLC counters can be built to either count up to or down from a predetermined value.

  • Every time the rung containing the up-counter is powered, the counter is advanced by one.

Counter Counting Sequence Up Counter

  • The counter will keep counting up until its total value equals or exceeds the preset value, at which point an output will be generated.

give a presentation on real time plc counter applications

  • Each time the rung carrying the counter is activated, the down-counter is reduced by one.
  • There is always a counter reset available to return the counter’s accumulated value to a specified value.

Counter Counting Sequence Down Counter

Representation of PLC Counter from different manufacturer

 The Allen Bradley, PLC Counter is represented as shown. In general there are 3 types. Up Counter – CTU; Down Counter CTD; UP/Down Counter-CUD

Siemens PLC Counter

In this counter there are following inputs and outputs are

  • Count up Input represented as “CU”
  • Count Down Input represented as“CD”
  • Counter Up/Down represented as “CUD”
  • Presetting Counter represented as “Preset”
  • Output of Current counter value is represented as “Accum”

         The accumulator value is raised by 1 each time there is a pulse at the CTU block’s input.

Siemens PLC Counter

         These are the blocks that are utilized in PLC ladder logic as counters. There are some inputs and some outputs on every counter block.

Inputs and Outputs

  • S refers to Set Input 
  • CU refers to Count Up Input
  • CD refers toCount Down Input
  • PV refers to Preset Counter Value
  • R refers to Reset Input Outputs
  • Q refers to Counter Status
  • CV – Counter Value
  • CV BCD – Counter Value in BCD Coded

give a presentation on real time plc counter applications

  • The current Counter Value(CV) will be raised by 1 for each pulse at the Count Up(CU) bit.
  • When the Set input (S) receives a pulse, the Presetting Value (PV) is set to the current Counter Value (CV).
  • The counter block is reset and the current counter value is set to 0 once more when there is a pulse at the Reset input(R).
  • The current Counter Value(CV) will drop by 1 for each pulse at the Count Down(CD) bit.
  • The count up and count down routines are also present in this block.
  • The current Counter Value (CV) will be increased at each pulse at the Count Up (CU) bit and decreased at each pulse at the Count Down (CD) bit (CV).
  • Presetting Value (PV) will be set at the current Counter Value when there is a pulse at the Set input (S) (CV).
  • The counter block is reset and the current Counter value is set to 0 once more when there is a pulse at the Reset input(R).

give a presentation on real time plc counter applications

  • The counter address is a data table address in the PLC-5 and SLC 500, but a predefined structure of the data type in ControlLogix.
  • The maximum preset and accumulated value for the PLC-5 and SLC 500 is 32,767, while the minimum value is -32,768; for the ControlLogix controller, these numbers are 2,147,438,647 and -2,147,438,648 respectively.

RS Logic Counter

Cascade Counters

  • Counting events that are more than the number permitted by a counter command may be essential depending on the application.
  • Cascading or connecting two counters is one method of achieving this.

Cascading Counters for Extremely Large Counts

  • Rung 2 & 3 – Counter C5:1’s done bit resets the counter when it hits 500 and increases counter C5:2 by 1 instead.
  • Rung 4 – After 500 times 500, or 250,000 transitions of the count input, the output light goes on.

Application of PLC Counter

Parts Counting Program

  • The total number of components leaving an assembly line for final packaging is counted by counter C5:2.
  • Each container must include 10 components.
  • Counter C5:1 sets bit B3/1 to start the box closure sequence when 10 components are found.
  • The total number of packets filled each day is counted by counter C5:3.
  • The daily total part and package count is reset to zero using a pushbutton.

Ladder Diagram of Parts Counting Program

  • Raw parts are fed into the in-feed sensor to start the operation, and each part generates an up count.
  • After processing, finished parts that arrive at the out-feed sensor create down counts, so the counter’s accumulated count continuously represents the number of parts that are still being processed.
  • The system is absolutely devoid of components prior to startup, and the counter is manually reset to zero.

In-Process Monitoring System Ladder diagram

  • When an automobile pulls in, it activates the up-counter output command and raises the total count by 1.
  • When an automobile drives away, it activates the down-counter output instruction and reduces the total count by 1 as it does so.
  • The accumulated amount will be the same in both the up- and down-counters because they share the same address.
  • When the total value reaches a certain threshold, the counter output is activated, illuminating the Full indication.

Case 1 : Assuming car slot vacancy of 100 nos. When the last car enters in indication of “FULL”

Ladder Diagram & Output of Parking Garage Counter Program

Case 2 : When a car goes out, after the Full the indication changes to “VACANCY”

Ladder Diagram & Output of Parking Garage Counter Program

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PLC Program for Bank Counter Application

A bank having three counters for Deposit /Withdraw cash in which totally 15 people are allowed for a day. When people count reaches 15, display will show Counter Closed and should not allow the 16th person to check-in. Develop a suitable program for this plc programming example.

Table of Contents

PLC Program for Bank Counter

PLC Counter Example for Bank

List of Inputs and Outputs

PLC Counter Example Inputs and Outputs

PLC Counter Example

Counter Example in PLC Programming

Ladder Logic Description

Latching rung to operate the system through Master Start and Stop PB.

When a person enters Counter 1, Sw 1 is pressed by the bank person to make count .One shot is used to give single pulse input which will be store in O:0/1

When a person enters Counter 2, Sw 2 is pressed by the bank person to make count .One shot is used to give single pulse input which will be store in O:0/2.Counter done bit is used to restrict the 16th person to enter.

When a person enters Counter 3, Sw 3 is pressed by the bank person to make count .One shot is used to give single pulse input which will be store in O:0/3

Collected outputs from the above rungs are accumulate in Counter block. Comparator block is used to limit the count by 15.

Counter (C5:0) done bit is used to refresh the Process from beginning

Program runs continuously until STOP PB is pressed.

Conclusion:

The above explained Bank counter  using PLC is for example only. It may vary from real time. We can use this example program to understand the working of Counters function in AB PLC.

Author : Hema Sundaresan

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COMMENTS

  1. A Simple Counter Application in PLC

    A simple counter application in the programmable logic controller (PLC) using a counting example on conveyor motor and proximity sensor.

  2. PLC Timers and Counters and Types

    Why timers and counters are used in PLC? A PLC is a specialized computer that is used to control and operation of manufacturing process or machinery. It is not possible to control complex systems by using certain logic and it is because we can't use sensors to check all the conditions.

  3. Using PLC Timers and Counters: Advanced Programming Techniques

    This tutorial-style article explores advanced techniques for utilizing timers and counters in PLC programming. It covers topics such as cascading timers, preset values, retentive vs. non-retentive timers/counters, and provides application-specific examples to illustrate their practical usage.

  4. PLC Timers and Counters, their types and Practical Uses

    PLC Timers and Counters are frequently used in industries for time delays and production monitoring. There are situations when you need to turn OFF a certain machine after some time, or you need to turn ON a machine after a certain delay when a sensor is activated or a button is pressed.

  5. PLC Counter

    What is the PLC Counter? We can define the counter in PLC programming as… an instruction which is useful for sequential counting as digital signal pulse or the number of digits. This instruction is denoted by the ' C ' in LD programming. And it is part of the mathematical function.

  6. Chapter 6 Programming PLC Timers and Counters

    Counters are used in applications that require items or products to be counted. A CTD instruction counts down on every false to true transition of the logic preceding the instruction and shares the same status bits, preset values, and accumulated values as the corresponding CTU instruction.

  7. Counters in PLC Programming

    A PLC counter is a function block that counts up or down until it reaches a limit. When the limit is reached the output is set. The thing is that counting is in fact widely used in PLC programming. Often you will have the need to counts different things. An example of this could be to keep track of how many times a process has been completed.

  8. PLC Series Chapter 7

    PLC Series is a beginner friendly video series covering all aspects of Programmable Logic Controllers including fundamental topics like Ladder Logic to more advanced areas of Human Machine...

  9. PLC Counter Programming for Beginners

    PLC counters are internal PLC instructions that can be used to count input or output signals in the PLC program. These counters operate like relay counters but you cannot hold a PLC counter in your hand and they do not need to be connected to wires to operate. Types of PLC counters

  10. PDF Programmable Logic Controllers

    One common counter application is keeping track of the number of items moving past a given point. Counters are similar to timers except that they do not operate on an internal clock but are dependent on external or program sources for counting. Programming Counter The two methods used to represent a counter within a PLC's ladder logic program are

  11. PDF Timer and Counter Instructions

    Counter Applications. For troubleshooting purposes, a counter can be used to monitor the steps of a sequential machine (e.g., a pneumatic robot). At the start of the sequence, the counters accumulated value is reset to zero. Each time the robot completes a step in its sequence, the counters accumulated value is incremented by one.

  12. PDF Teaching PLC Timers and Counters Programming

    The use of mobile applications in the context of teaching PLC programming techniques is addressed in this work. The MIT App-Inventor II is deployed to develop mobile applications for learning purposes. An android based application entitled Time-Counts is proposed here, developed to support the teaching/learning process of both Timers and Counters.

  13. PLC Counter Instructions

    A counter is a PLC instruction that either increments (counts up) or decrements (counts down) an integer number value when prompted by the transition of a bit from 0 to 1 ("false" to "true"). Counter instructions come in three basic types: up counters, down counters, and up/down counters.

  14. PLC learning Series 13: Counters in PLC

    The counting frequency of the code counter of a normal PLC can exceed only tens of Hz (depending on the time of the scan). If the input signal frequency is higher than that, the high-speed counter (HSC) must be used, otherwise the count of losses or even the counting that occur. This counter uses 2 inputs: the first is the RESET input which ...

  15. Chapter 6 Programming PLC Timers and Counters

    Cascaded timers are used to start equipment sequentially, such as when starting three conveyors with a 10 sec delay between the start of each conveyor. Chapter 6 — Programming PLC Timers and Counters. Counter instructions contain three words. The bits and words of counter instructions have addresses that can be used in the program of a PLC.

  16. PDF TIU

    LEC 6- Counters in PLC Counters are similar to timers except that they do not operate on an internal clock but are dependent on external or program sources for counting. 1. Counter Limits Counters use variables of certain data types to store numbers in the PLC. All counters need to store at least two numbers: 1.Counter Limit 2.Current Counter Value

  17. Understanding PLC Program Commands: Up and Down Counters

    Count Up (CTU) and Count Down (CTD) instructions in Studio 5000. When we trip Input, the CTU adds 1. When we trip Input2, the CTD subtracts 1. Because it is the same set of Counter tags (as indicated by the identical tag name 'Count' in both counters), the preset is the same on both. If you change one, it will change the other to match.

  18. Top 43 Applications of PLC in Industry and in Daily Life

    What are the Applications of PLC in Daily Life and in Industry? 1.Industrial Applications of PLC 2. Power Station Applications of PLC 3. Commercial Applications of PLC 4. Domestic Applications of PLC 5. Education Applications of PLC What are the major areas of Application of PLC? What are the Applications of PLC in Daily Life and in Industry?

  19. PLC Counter

    Up Counter (S_CU) For each pulse at Count Up (CU) bit, the current Counter Value (CV) will be increased by 1. When there is a pulse at Set input (S), it will set Presetting Value (PV) at the current Counter Value (CV). When there is a pulse at Reset input (R), the counter block will get reset and the current counter value is set at 0 again.

  20. Basics of PLC Timer

    For the ladder diagram programming, the classification of the PLC programming timer is-. 1. On Delay Timer (TON) An on-delay timer (TON) is a programming instruction which use to start momentary pulses for a set period of time. Let's see, a simple construction of the AB PLC On-delay timer programming instruction. 2.

  21. PLC Counter instructions

    A counter is a PLC instruction that either increment (counts up) or decrements (counts down) an integer number value when prompted by the transition of a bit from 0 to 1 ("false" to "true"). Counter instructions come in three basic types: up counters, down counters, and up/down counters. For both UP and Down counters there … PLC Counter instructions | Example for counter logics Read ...

  22. PLC Counter Instruction Types

    The Allen Bradley, PLC Counter is represented as shown. In general there are 3 types. Up Counter - CTU; Down Counter CTD; UP/Down Counter-CUD. In this counter there are following inputs and outputs are. Count up Input represented as "CU". Count Down Input represented as"CD". Counter Up/Down represented as "CUD".

  23. PLC Program for Bank Counter Application

    Counter (C5:0) done bit is used to refresh the Process from beginning Program runs continuously until STOP PB is pressed. Conclusion: The above explained Bank counter using PLC is for example only. It may vary from real time. We can use this example program to understand the working of Counters function in AB PLC. Author : Hema Sundaresan