Scaling High Speed Counter Inputs - ML1400/Logix 500

[TimD]

Hello,

Got some help wiring and setting up my flowmeters on these threads. Now, I must scale the inputs. I've done this many times with the SCP block for analog inputs, but I'm sure the pulse input method is different.

I will be dividing my flow rates by minute, then totalizing, then resetting the accumulator for the next minute.

I have a flowmeter with a K factor, factory calibrated.

I need to scale so that my instantaneous 60 second flow value can properly be added to my totalizer variable. I think I have an idea on what to do, just need a little help on the how part!

Thanks All,

Tim

 

[TimD]

Still having a hard time with this one. Not that I can't scale, it's how to correctly time the events so that I don't miss any precision.

I have a flowmeter with a K factor of 1456, equal to 1 gallon.

I have an STI file set up to read the flowmeter via HSC2 (input I have wired) and reset the accumulator each second. The accumulated value is converted to float, multiplied by 60 to give me instantaneous GPM, and it seems to work.

Now, I want to capture this value each second, add it up 60 times, then add the 60 second total flow to a master totalizer, then reset the 60-second accumulator.

My issue is, are timers accurate enough for the task, or can I somehow use the same STI to trigger the addition and totalization? Can I use a nested timer, or do I have to use count up, etc.

I attached an RSS (.PLC) file for those interested in helping. My current program uses a timer, but only grabs the 60-second instantaneous flow value and adds it to the master totalizer every 60 seconds, not very accurate.

Thanks All for the help. This one's tougher than I thought.

Also, is there a cleaner way to do 6 f these? Thanks!

Have a good weekend. I'll be checking in...

 

[bernie_carlton]

In the STI latch a bit at the end of the STI.

In your standard program, if the bit is true then add all the one second readings to the accumulating one minute readings and increment a counter (preset to 60). If the counter is done then add all your one minute readings to the final accumulation and zero them all and unlatch the bit.

If your main program scan time is under 1/2 second (which it should be) then there should be no problem with the 1 second STI interrupting this 'add then possibly clear' routine.

 

[TimD]

Thanks Bernie,

I'll give this a go!

 

[bernie_carlton]

and unlatch the bit.

I grouped that phrase incorrectly. You will unlatch the bit each time, not just if the 60 time (one minute) counter is done.

 

[TimD]

Thanks, Bernie.

I have it going now! It's a bit of code to read 6 flowmeters, so I'm going to learn subroutines in 500 to make life easier.

You are a great asset to these boards, many thanks again!

Tim

ps - for anyone wishing for the code, PM me. It is commented enough, but could be put in a subroutine for cleanliness...

 

[piscis]

Tim:

I'm doing a similar project, can you post the code you have so far?

Thanks