Monday, May 25, 2009

Minisystem Controls Blending (Flow) Ratios

A very simple "system", but it solved our customer's problem.

The need: our customer needed a simple way to control the blending proportion (ratio) between two pump flows. The user desired a ratio adjustable from 1:5 to 5:1, with the center of the adjustment range being 1:1.

The pump controller's input was a standard 4-20mA dc control signal (4mA produces zero flow, 2o mA produces maximum). Our system needed to take the input (flow #1), multiply it by the ratio and produce an appropriate 4-20mA output (flow #2).
The solution: our JH4410 multiplier module plus a 10-turn precision potentiometer. The JH4410 was modified so that input B was the potentiometer's position. (Input A was set up for standard 4-20mA input.) The output's 4-20mA signal was proportional to input A multiplied by the potentiometer position. Additional modifications created the desired dial settings - 1:5 (gain = 0.2) at zero turns, 1:1 at five turns and 5:1 (gain = 5) at 10 turns.
At the customer's request the system was mounted in a wall-mount industrial enclosure.
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