LOL gotta love the 'net.
Anyway, I am trying to understand OPs process.
Is the duty cycle of the actuator used when moving the valve, i.e. when either opening or closing, presumably to keep the actuator motor from overheating, which it would do if it ran continuously?
So the command to the actuator is one of three discrete values:
- Be closing - actuator motor runs, with 75% duty cycle, moving valve toward fully closed
- Be opening - actuator motor runs, with 75% duty cycle, moving valve toward fully open
- Be holding - actuator motor does not run, valve holds position
So there is no feedback of the actual valve position, e.g. 0% (closed), 100% (open), 50% (half-closed/-open), 42%, etc.
Meanwhile the PID tries to drive a pseudo-analog measured Process/Present Variable feedback value to a Set Point by varying its pseudo-analog output Control Variable value.
And OP's query is how to map that
pseudo-analog, continuous PID output CV signal to one the three
non-analog, discrete states* of the physical control device, i.e. to the controller board of the electric actuator?
Also, I am not sure I understand this:
I have an electric actuator with a 75% duty cycle ... how do I make sure that the valve doesn't cycle to much and go outside its duty cycle.
Isn't the duty cycle a property of the actuator and its controller board? How could the valve (motor) "go outside its duty cycle?" Is that problem that, if the input signal to the controller board is shorter than the cycle time, the motor could start, get part way through its 75%, then stop briefly before another input signal starts it on another 75%, etc.?
* be closing, be opening, be holding