Regulating pump output with load-cells

[Lancie1]

By Hubert's request, here is a RSLogix 500 example (Ladder 4 only of a program that has 9 similar pumps) that uses the Loss-in-Weight of a container (burette) to control the speed of a variable speed drive for a small pump. This is a dosing pump that puts out drops, but the principle and calculation methods for a large pump should be the same.

The PID instruction is on Rung 12. Rung 13, Output O:7.0 is the analog 0-10 volt signal to the Pump variable speed drive. Maybe the rung comments will help to explain each rung.

Most of the other rungs are for controlling the refill of the burette (test-tube-like container) from the nurse tank, and to scale the various parameters for display on a RSView screen.

 

[Hubert12]

By Hubert's request, here is a RSLogix 500 example (Ladder 4 only of a program that has 9 similar pumps) that uses the Loss-in-Weight of a container (burette) to control the speed of a variable speed drive for a small pump.

The PID instruction is on Rung 12. Rung 13, Output O:7.0 is the analog 0-10 volt signal to the Pump variable speed drive. Maybe the rung comments will help to explain each rung.

Most of the other rungs are for controlling the refill of the burette (test-tube-like container) from the nurse tank, and to scale the various parameters for display on a RSView screen.

Thanks a lot!

 

[Lancie1]

The idea is to regulate the pump's frequency output according to the funnel setpoint weight with PI controller.

If this is a true description of your problem, it implies that the funnel is being filled continuously, and your goal is different than the example that I posted. For my example, the goal was to control the pumping rate into a chemical process at a constant Setpoint.

In your case, the goal seems to be different- controlling the level of liquid in the funnel, while it is being filled by another source. So I am wrong- if you only want to control the level (using the proportional weight) then simply take a weight reading every 1 second, and use that weight as your Process Variable, with a Setpoint and PI controller to set the speed of the pump, so that the tank level remains constant.

 

[Hubert12]

If this is a true description of your problem, it implies that the funnel is being filled continuously, and your goal is different than the example that I posted. For my example, the goal was to control the pumping rate into a chemical process at a constant Setpoint.

In your case, the goal seems to be different- controlling the level of liquid in the funnel, while it is being filled by another source. So I am wrong- if you only want to control the level (using the proportional weight) then simply take a weight reading every 1 second, and use that weight as your Process Variable, with a Setpoint and PI controller to set the speed of the pump, so that the tank level remains constant.

I was just about to write that, however thanks for sharing your work because it is always extra experience to analyze sb else's program.

 

[Lancie1]

To determine your constant Setpoint, you can fill the funnel up to the top of the sloping area, then read the weight. Make that your permanent Setpoint, and set your PI gain and reset parameters so that the Setpoint weight is maintained.