When using analog, choose a sampling period and once a period, take the instantaneous flow rate, multiply by the period length and add to the total. Shorter periods will be more accurate because the method assumes that the flow is constant throughout the entire period. In some scenarios you must compensate for scan latency. Say you have a 500ms recycling timer in a program with a scan time of 6ms. If you just let the timer recycle itself with an NC DN bit on the input, then on average, your timer will recycle every 503ms (500 + 6/2). So if you want it to be accurate, you can do a couple things. If there's an internal flasher bit near the period you want to use, say the one second ST4 bit, use a differential of that, as there's no accumulated error, or instead of simply recycling the timer, you can subtract the nominal period length from the timer accumulator (don't think I've actually tried this with Do-More, so I don't know if it will let you manipulate the timer accumulator). That way, when you see the timer has expired, on average at 503ms, and you subtract 500ms from it, you have a 3ms head start on the next cycle, or 1/2 scan, which eliminates the error due to scan time latency.
Topic: Flow Totalizer (Read 7477 times)