PID Override

[Magical Marshmallow]

Hey,

I am trying to put a boolean into manual override switch into my PID setup for a temperature control.

In order to do this, I want to have a numerical control which is in oC on the front panel. However my heater will respond to Volts. In order to do this I have put in a mathematical formula.

The Result of the formula, the Boolean and the output of the PID are wired into a Select VI.

When they are wired in, I get the following Error "The Wire connects to a Polymorphic Terminal which cannot accept this data type.

How do I make this override switch (So that the temperature can be set in oC from the front panel)

Cheers

[ntaINC]

MM,

I am not sure I understand your system. It looks like you're measuring a thermocouple and you want the temperature to stay at a certain setpoint. I also see that the output of your PID VI is 0 to 100 'volts' and that you then perform a function on this before sending to your device for controlling temperature.

You want to be able to set the temperature from front panel. From what I see, you shouldn't need a manual override; just change the value in the setpoint control. A manual override would be used if you needed to specify the temperature controlling device to operate at say 50% and not worry what the temperature was.

Your broken wire is because the Express VIs use a Dynamic Data Type (DDT) and apparently the Selector VI does not automatically convert to this. You should be able to inset the Convert To DDT VI on the output of the PID VI to fix the broken wire. I haven't tried it, but it should work. I am just not sure that your override will work as you anticipate.

Tessa

[Andy_C.]

Hello,

I can see possibly the following solutions

1. Convert control effort out from PID VI in to dynamic data type

2. You can try using Formula Node, Expression Node, or MathScript RT Module for your mathematical formual and output a DBL output.