PLC programs usually just control the logic between the inputs and outputs. If this turns on and that is not on, then this output is on, bla bla bla. Programmable logic controller programs can go far beyond just the basic logic. Modern processing power has enabled allot more features that can be programmed.
Traditional PLC programs are written so everyone can understand the ladder programming. This is not the case anymore. There should be no need for anyone to review the ladder program. Error messages, alarms and sequencing should automatically make troubleshooting simple. If something is not working, your system should direct personal how and what to do to fix it.
Touch screens, LED indicators, stack lights, custom user error messages, display boards and logging software are just a few methods of displaying information to the operator, electrician, mechanic, supervisors, managers and even owners of the equipment.
Your program can track the basic hours of operation and trigger maintenance events from these hours. What needs to be done after 100, 500, 1000 hours? Just like the service on your car, you should plan for the service on your machine through the use of program.
If a pneumatic cylinder is used here are a few things that you can track in the program:
- Number of cylinder cycles
- Life expectancy
- Time it takes to complete cycle (Sensors on both ends of the cylinder)
- Determine if a seal is leaking
- Pressure of the incoming supply if multiple cylinders are monitored
http://www.bimba.com/Global/Library/Catalogs/Bimba%20Catalogs/BimbaRefHandbook.pdf
Alarm Screens:
Alarms should be easily identified and located.
Remember: A picture is worth a thousand words.
Establish sequencing of events that can be stepped through forward and backwards can allow maintenance personal to easily troubleshoot the system without going through possibly hundreds of lines of ladder logic.
Please see the following links for sequencing your program:
Building a PLC Program That You Can Be Proud Of - Part 1
Building a PLC Program That You Can Be Proud Of - Part 2
With Ethernet connections built into most modern PLC CPUs, it is now possible for the PLC to automatically send email to your exchange server.
Automation Direct Do-More CPU is one of these PLCs.
http://www.automationdirect.com/adc/Overview/Catalog/Programmable_Controllers/Do-more_Series_PLCs_(Micro_Modular_-a-_Stackable)
When programming PLC's for logging data, information must be stored in the PLC for later retrieval. Most commercially available software for logging data does not consider the event of loosing the communication cable. If an interruption on your communication lines happen, data cannot be retrieved from the PLC. The PLC can use indirect addressing to store the logged information. Logging software can read the pointer to the logged data, read the data and then reset the pointer. The duration and amount of information that you are logging will determine the amount of time the communication can be disabled before loosing data. I usually log daily summaries as well as detailed information in the process. My detailed data will be lost in 2 hours but my log daily will take one month.
What other options do you see with a modern PLC?
I look forward to your comments,
Garry
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