Hello,
Hoping for a little insight on this Counter Card. I am new to a small company, they've have many 'issues' ongoing for long periods of time that never got solved. One comes from an HSCE2 Card. What they are doing is taking the Rate value off a HSCE2 counter card, and converting it into FPM. They actually had the scale improper, but I fixed that. (They were always showing ~11% faster run rate than actual because improper values in Scale with parameters function). Now that I have fixed that what they did is took that Rate value converted into Feet per minute, then scaled that from 1-32,767 and set it out as a differential analog output, going to the analog input of another PLC. In the other plc, once they re-construct it back to a FPM calculation it gets strange again.
They take 60 seconds and divide it by the FPM. This makes sense I believe, because say 100 Feet per minute. 60 seconds / 100 feet per minute = 0.6 seconds per foot ran. They then take this 0.6 seconds value that is obviously a constantly updated variable depending on how fast they are running and moving it to a Preset value of a timer. Now they use this timer to generate a 'Pulse' for every foot ran.
After fixing the Rate value to get the proper FPM, I replicated this conversion to the foot pulse they made, which of course ends up with a x100 because the timer is in Deci-seconds in the SLC 5/04, and something doesn't add up. If I put a 60 second timer after 60 seconds move the count into a holding register to view it, it is always way less than the FPM from the rate value, which has been verified to be correctly monitoring the speed now. I mean, say the timer preset value is 0.7 seconds. 60 seconds / .7 seconds = ~85-86. So after 60 seconds, it wont have counted the counter to 85 or 86, it will be like 80. Is this a scan time issue? I mean logically speaking if I put a .7 value in a timer, and have its own XIO .DN instruction resetting it every time it finishes, as fast as the scan can reset it, and then immediately under that the XIC .DN bit counts up a counter by 1, THEORETICALLY, after 60 seconds I should have my full count, not drastically under.
Is this why the HSCE2 card gives a rate value AND a counter, because using one to mathematically construct the other in the processor is an inaccurate process? The counter is hooked up as well on 1024 PPR pulse tach, so on the front end the PLC it goes to has an accurate count. But then they send rate value over analog signal to other PLC , rate value now seems accurate after fixed scales, but the construction of a 'Foot counter' from the rate value is not working properly. Could I send the "count value" over an analog channel as well? Scale the 0-1024 PPR to 1-32,767, then on input side take the 0-10000 mv and scale back to 0-1024?
Sorry for the text book!