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quantity of each product in barrels on a touchscreen, and amounts of each product will be measured with turbine meters. The rate at which

one product is pumped is constant, and the rate of the other can be throttled with a control valve. The customer wants the process to

operate such that the products will mix evenly throughout the pumping cycle. So, at the end of the run both pumps will finish at the same time having pumped just the right amount of each. I'm attempting to accomplish this through the use of a PID block in a Modicon PLC. My question is this: What is the better way to establish a setpoint for the loop? I can use the values input by the operator to find the percentage of variable rate product to constant rate product. Then should I measure the current volume pumped by the constant rate pump, find the volume the variable rate pump should have pumped and use

this as the setpoint, or should I express the setpoint as a flowrate based on the rate of the constant rate pump? As this is my first

experience with PID control any help would be greatly appreciated.

Brady Matherne

PLC / SCADA Tech

Panel Specialists, Inc.

[email protected]