PID/Flow Control


Thread Starter


Hi everyone,

Currently I'm working on open loop process project where there are two fluids going to mixed inline before delivering to a drum.

Basically, the process is 2 inputs and 1 output, the first input is slightly change in in terms of density when it comes from supplier. The second input (chemical liquid) is the main input that if i control it probably i can reach my set-point (density).

no valves included so i have to control the speed of the both pumps. i think if i consider the first input as disturbance as its vary.

There will be density sensor to measure the output (my feedback signal) goes to the PLC Controller (Allen Bradley), VFD between the PLC and the Pump. also i have density sensor to measure density for the first input.

so the question here is: do i need flow meter to measure my second input to control the speed of the pump based on my density feedback signal? or just by using the density sensor from the output i will be able to control the speed of the pump based on my set-point?

whats the proper way to design a closed loop system? and is there other hardware requirement that i need?

also i need a help to construct the feedback and feedforward control strategy to reject the first input disturbance or any recommendation please.

Thank you very much
I'm going to call the products A, B & A+B. It depends really on how accurate it needs to be.

I assume you read the density of A with a simple Hydrometer before you start. so from there you should know how much of B you need to add to get the correct A+B.

You may be able to control it by having one pump A at a fixed speed and the other Pump B at a ratio of the first with a fudge factor to correct the density say +/- 10% speed determined by the feedback density meter.

It would be easier if you knew the actual flow rate, coreolis meters often have a density output as well as flow.