Tag Archives: plc ladder logic examples

Productivity 1000 Series PLC Numbering Systems and Tag Database

The Productivity Suite Software allows us to use tags in the PLC. Tags are a method for assigning and referencing memory locations within the programmable logic controller. They allow a more structured programming approach and are stored within a tag database. The tag database is stored in the memory of the Productivity Series of PLC’s from Automation Direct. Do not over think tags. Tags are just names that we assign to variables of any data type stored in the PLC memory.

We will be looking at data types available in the Productivity PLC and how to use the tag database. Let’s get started. Continue Reading!

Productivity 1000 Series PLC Monitoring and Testing the Program

The Productivity Suite Software provides tools for us to monitor and test our programs. Last time we used Tag Names and Details, Task Names and Descriptions, Rung Comments and Instruction comments to document our first program and transferred this to our connected Productivity 1000 Series PLC. We will be monitoring our ladder using the ladder editor window and display the information two different ways. Data View is a powerful tool to help us to test and view our program. We will be forcing the IO, toggling the IO view and graphing our tags to test our PLC logic circuit.
Let’s get started. Continue Reading!

Productivity 1000 Series PLC Establishing Communication

We will be connecting the Productivity 1000 Series PLC with our computer running the Productivity Suite Software. A micro USB and an Ethernet (RJ45) communication link will be made to our programmable logic controller.
The latest Productivity Suite software version is 3.1.0.11. This is the programming software that we will be using to create our logic for control.

Let’s get started. Continue Reading!

PLC Fiddle – Online Editor and Simulator in your Browser

I have recently come across a free virtual plc simulator called PLC Fiddle. It will enable you to create simple PLC ladder logic code within your browser. This is an ideal way in understanding PLC concepts for industrial automation. All of the basic PLC instructions that come with most plc units have been incorporated in this virtual PLC software.
PLC Fiddle is currently in an early stage of development but is functional enough to be helpful to you in learning and understanding PLC concepts. We will be reviewing this software and creating a few common basic circuits. Using the simulator we will test our circuits and monitor our PLC programs (circuits). Let’s get started. Continue Reading!

How to Troubleshoot a PLC

Your control system does not work. Where do you start? Lets walk through a series of questions in order to determine where the problem lies.

footprints

Is this a new installation or previous installation that was running fine? Determine if system has been running well in the past and has currently stop working correctly. This is the indication that the problem relies inside the system.

Is there anything that has happened outside of the system? Has there been a lightening strike, blown drives on other systems, etc.  This can point to the original cause of the malfunction.

build-2Bgear-2Btower

What is the system doing now and what should it be doing? Gather all of the information you can from every resource you can.

  • Supervisors  – machine, location, time of error, other happenings in the plant, etc
  • Operators – What is it currently doing? What should it be doing? What do you think is wrong?
Operators of the equipment are your key resource in finding, correcting and ensuring the error does not happen again. They know the equipment from an operational point of view which can assist you greatly in troubleshooting.

PLC fatal and non-fatal errors:
If the machine is still running partially then this is an indication of a non-fatal error. Cannot run at all is usually a fatal error.

Do_More CPU Units

Take a look at the PLC indicator lights on the CPU. Refer to the operation manual for the PLC for troubleshooting specific lights on the CPU. The following are general tips:

If no lights are on then the possible cause is a power supply. This is usually the most common of errors on a PLC system. Mean time before failure (MTBF) is rated on the lowest rating of components which is usually the power supply.

If the run light is on and an error light flashing this usually indicates internal errors such as batteries, scan time, etc. It is usually not the reason for the lack of operation.

If the run light is on and no other errors are seen on the CPU we can put the PLC program on the bottom of the list of items that could be the cause.

Check the input cards of the PLC. You should see the individual sensors lighting up the inputs. If not then check the power supply to the input card / cards.

Ask the operator what is happening and what is suppose to happen. Try to follow the sequence of events in the PLC to determine either and input or output device not working.
Some items to watch:

If this is a new PLC program that you are doing start with a logic flow diagram. This will determine the procedure to start programming.
Every program can be done in several ways. The best method is the most documented one.

Documentation is the mark of a good program.

PLC-2BScan

Some trouble with new programs can be racing conditions. This is usually a case of not understanding how the PLC scans logic. In general the PLC will scan from left to right, top to bottom. The output bits / words are available to the inputs of the next rung of logic. (Modicon PLC’s will scan differently.) Actual outputs and inputs are not read until the end of the scan of the PLC. Racing conditions happen when the output is set on multiple rungs, but will not get actually set until the end of the scan. Think of it as the last action will always win. So if this happens move the logic to the end of the program and see if it works. Then go back and see where the output was also set.  Cross reference guides are ideal for this purpose. (Refer to your programming software on how to get cross references.)

start stop 011

We have discussed just a few troubleshooting techniques. Hopefully now you know how to start looking for the errors on your  system. Let me know how you make  out.

Watch on YouTube : How to Troubleshoot a PLC

Do you know of additional tips or methods to share?

If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.




The Secret of Using Timers

Timers are used in the majority of PLC programs. There are also a wide variety of off the shelf industrial timers that you can use. The implementation of timers can be vast, however it all starts with a TIMING CHART.

A timing chart is the secret behind understanding of the timer that you need in your application. Making a timing chart before writing the program will ensure that all of the information will be accounted.

The timing chart is mapped out on a x and y plain. The ‘y’ plain has the state of the input on/off (1 or 0). The ‘x’ plain will show time.

Lets take a look at a timing chart for an On-Delay Timer. This is the basic operation for an Omron H3BR industrial timer.

Timing Chart On-Delay Basic

Power –  When dealing with PLC’s we must consider when power to the unit is removed what happens to the current time and output conditions.
Start – In this case the start signal is momentary to start the time cycle. (t) We could modify this signal to be maintained until the output switches.
Output – The output will show when it turns on. This can also indicate the opposite, and show when it turns off.
Time – Time is shown by the relationship between the start signal and the output. Our example shows timing starts on the leading edge of the Start. This could have also been on the trailing edge.

Here is the same on-delay timing chart with some more detail. Several conditions are added to the chart.

Timing Chart On-Delay Details

These conditions prompt us to ask the following questions.
What happens when:

  • Power is removed / restored
  • Multiple start signals are received
  • Do we need a Reset signal. If so what happens during its operation
  • Do we need a display of the time. Present Value (PV) / Set Value (SV)

As you can see the timing chart is vital in determining how the sequence will be performed. This is the exact same method that I use when determining timing sequences in a PLC program.

Lets look at an example.

Motor_Sequence

When we hit the start button, the warning light then comes on. After a fixed time the warning light goes off and the motor starts. The motor will run until the stop button is hit.

We will start by using the Start / Stop Circuit we did earlier.

Timer Program

You will notice that we have added an internal memory bit (C0) as our Start Sequence. This is a memory retentive bit, so we can use the (ST0) $FirstScan to make this circuit non-memory retentive. If power goes off, or the PLC is put into program mode the circuit does not remember the last state. It will default to be off.
The sequence is as follows:

  • Start pressed
  • TMR starts to time (10seconds)
  • Warning output comes on
  • After TMR (10seconds)
    • Warning output goes off
    • Motor output comes on
  • Stop pressed
    • TMR is reset to 0
    • Warning light off
    • Motor is off

Every PLC has timers. They all have different types depending on what you are trying to achieve. It will all start with your Timing Chart.

Watch on YouTube : Learn PLC Programming – Free 8 – The Secret of Timers

If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.