a PID control problem...

[theripley]

here's the scenario: we have started assembling a machine that mixes fuel & water on the definite volume ratio, 7:3 to be specific..the idea is simple, from fuel tank, a motor pump will supply the oil (fuel) to the agitator (mixer) with the motorized valve controlling the exit of liquid..same is true with the water, which will supply liquid to the agitator at the same instant the fuel is release..our problem is that, the valve controlling the water is not a motorized valve but rather an ordinary valve controlled in an on-off manner whereas the motorized valve is controlled in a PID manner..can you recommend a control method that would give us our required volume ratio given the controlling element outputting differently..any idea would be greatly appreciated..


Bless you,
theripley

 

[bigrthanur]

I have done this using a PID instruction. but for the output use a move to and put it in the value of a timer. Use two timer one would be your output on time and the other would be you output off time.