If your PID output is between -100% to 100%, you can try to do something
like this :
Compare output with Zero, and wire as case box
If greater put your first relay ( for heating) to ON (or off depend on
your process), and wait a time of X.Pid output
(for example PID = 50% waiting = 500 ms, PID = 100% waiting 1000 ms, and so
on ...)
After waiting invert the digital ouput
If lower make the same action with the second relay (for cooling if exist)
and wait the absolute value of Pid.
You can have better result with a third state case, for example :
Less than -10 : R1 On, wait Pid.X, R1 Off
Between -10 to +10 : Nothing, the system is stable and the control loop can
terminate
greater than +10 : R2 On, wait Pid.x, R2 Off
good luck
Ian Paul Barber a
écrit dans l'article
<7r38ci$1tg$1@hecate.umd.edu>...
> I need to control a relay switched heater (the heater
> is either on or off - no ramping of voltage up or down)
> with a LabVIEW PID routine. So my PID output will be the time
> controlling on cycle of the heater, switched using a relay.
>
> Can anybody recommend ways I could go about using LabVIEW
> to translate the PID output of a duty cycle time to
> controlling the heater using a SCXI-1161 relay card.
> Any help is appreciated.
>