Flow integration using PLC5/20

I have a need to do some totalizing based on an instantaneous flow, client needs to know how much they pumped down the pipe in the last 24 hours etc.

The flow is scanned by the AB PLC-5/20 from AB remote IO via DH+ network and was wondering if it is even possible to do with this processor. Has anyone tried this and how accurate do you think it would be to do it this way.

Thanks

The PLC5/20 is an enhanced PLC5, it won't have any problems whatsoever doing the totalizing. But as far as overall accuracy, that depends a lot on how fast the flow rate is changing and how long it takes to get that data back over RIO. If the flow rate doesn't change all that quickly, then a simple periodic summing should give you decent results. You need to keep the scan time from becoming a part of the time period over which you are calculating the flow - this is easy to do if you don't reset the timer but use a comparrison and manipulate the timer ACC instead of resetting it.

Example below:



See PDF for ladder ( ladder file (subroutine) 7 is called every 1 sec per STI)

Can the existing flow meter generate a pulse output?
If you have a slot open, installing a 1771-CFM would be the ideal solution. Using the CFM module you can have accurate totalizing by counting pulses and flow rates based on pulse frequency.

Refurbed price for the CFM module is around 1500 USD.

Option D

Assuming that your flow signal is read using a 1771-IFE module, I think your best bet would be to use the real-time sampling feature of the module. You would not need a timer or STI. The BTR DN bit will only go true after the module has updated and you can be confident that the reading is fresh and taken at the interval you have specified.

For totalising, I would use the average of the current and previous reading multiplied by the sample interval.

Trigger the totaliser with the BTR DN bit and then re-trigger the BTR.