Flow rate totalizer

I am using Allen bradley controllogix 5000 and i need some code for a totalizer.My flow rate is an analog input of 4-20ma.

The best way to get total flow is to configure your flow meter for pulse outputs, and count the pulses.

As an alternative, you can use some math and get flow rate for a set time period and then calculate the flow total, but it will not be 100% accurate, it will just be a calculated flow total, the accuracy will depend on your sample time, and how steady the flow rate is. Even with a short sample time, and a consistent flow rate, you will lose some accuracy during the flow start up and shut down.


In the future, it would be better to post in the main forum, as not everyone checks the practice area.

If you have the process extensions for Logix 5000 you can use the standard totalizer function block which is quite capable and should meet your needs. RS Logix 5000 Professional Edition provides this.

If you want to do this in ladder logic, suggest you set up a 6 second (1/10 of a minute for ease of calculation) timer and calculate Reimann sum (from calculus).
http://www.math.hmc.edu/calculus/tutorials/riemann_sums/
This is what Ken is suggesting in his post to your question. The loss of accuracy for consistent flow rates or not noisy flows is usually good enough. If you need more resolution to catch quickly changing flow rate signals, then change from 6 seconds to something smaller. Don't forget to scale the flow total on your time base though (ie convert units correctly). For example Flow Rate in gpm and 6 second (1/10 minute) timer will totalize as gallons x 10. Gallons/Minute x 1/10 Minute (check my math/units conversion).