Add a delay to the setpoint ramp vi?

[mittleiderj]

I'm using the PID Setpoint Profile vi with the PID Autotuning (Temperature) vi to control a heat blanket with multiple thermocouples (as many as 48 thermocouples). The process uses the maximum value as the control point. The process must follow a ramp rate and then hold for a prescribed period. This all works fine except for a slight twist that I can't seem to account for.

As part of the process, it is required that all of the lagging thermopcouples must be above a minimum threshold value prior to starting the hold. I can detect when the lagging thermocouple exceeds the threshold but what I can't do is cause the Setpoint Profile vi to pause while waiting for the minimum threshold requirement to be met.

Is there a trick to holding the Setpoint Profile vi or do I need to create my own ramp and hold generator. Has anyone done this?

Thanks for any help.

[sassyaspy]

Hello mittleiderj,

Could you make a case structure in your control loop with a Ramp and a Hold case, where in the Hold case you preserve previous values in shift registers? You might have to preserve time between cases as well. From what I understand the Setpoint Profile VI does not have a pause function because it only executes one setpoint value generation each time it is called. 

Hope this helps!

[mittleiderj]

sassyaspy,

Thanks for the input,

Yes, I have started a new subvi using a cse structure as you suggest. I have come to the conclusion that the Setpoint Profile vi will not due in this case.

I'll post the subvi when I have something working.

Have a great holiday.