Run Time Meter

I have a task to create a Run-Time-Meter for a pump. I am using Modicon Momentum and Concept to do this. I am trying to keep track of the run time for three pumps and use that to stage them based on the run time (to make the run hours equal).

Ok. Sounds reasonable. What's the question then?

Steve

Elapsed Time Meter

I have been trying to use timer block but was not able to make the hoding register to keep the final time. I lose the accumulated time. The question is: is there a function block that doe Elapsed Time Meter function with out having to write one.

I am afraid I don't know your specific PLC, but based on the pump control project you describe, my best guess is that you are probably going to have to build some kind of timing logic no matter what kind of timers the PLC has. I say this because usually we want pumps to run for a 200 or so hours before switching to the next and most (if not all) PLC's are not equipped with timers that can time that high - hence, you have to roll-your-own.

My suggestion would be to create yours using a mixture of timers and counters. I would start by creating a timer that resets itself every minute. Each time it times-out, increment a counter for the pump you have running.

Along with that, create the logic that determines which pump should be running. This will probably be in the form of counter comparisons for all three pumps.

Hope this helps.

Steve

As an addendum to Steve's good advice. If your PLC supports Retentive Timers, that will give you a more accurate time. It may not matter if the pumps run more or less continuously, but will help if they cycle on and off a lot. I don't know your Modicon, the last one I worked on was the 984. In an AB PLC, it would be an RTO.

Stu....

This subject has come up many times on this forum. Try a search to see what others have said.

If your PLC has a 1 second pulse, use it, anded with a "pump running" logic signal to increment a counter to "36" seconds. When the 36 pulse counter comes true, reset it and add "1" to a regular old data register. That "1" will represent 1/100 of an hour. (If you wish to display it as "hours", divide by 100, that is if you have floating point math.) Every 36 seconds you will add another "1" to your data register. That register will hold the "run time" for that pump in 1/100ths hours. Three Pumps? Three counters and three data registers. Data registers are rententave.

When you go to start a pump, perform a comparison on each "run time" data register to determine which contains the lowest number, and start the associated pump.

If your pumps tend to run all the time, use a "clock". Some PLCs have realtime clocks built in, some you can ADD them, or you can build your own with cascading counters. Every night at midnight (for example), or everytime your self built clock reaches the appropriate number of hours, do the comparison routine again, on all of the "run time" data registers described above, and start the pump(s) with the lowest number in it's "run time" data register.

That way all your pumps can wear out at relatively the same time, so when you send the first one that fails to the repair shop, the other two will be on their last legs also.

:8|

Stationmaster