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cmad95

FX5U IQ-f series PID for Tank temperature control

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Hello,

I have use case for my FX5U-32M PLC controller that has an analogue output module that is hooked up to a 10V trigger SSR heater. I want to use the PID function output (MV) to control power output of the SSR heater (0 - 100%). My measurement value (PV) is an analogue input from a temperature sensor between (0 - 400C). With a temperature set point somewhere between that. I figure that as long as I know the percentage power I need to use,  I can use a pulse width modulation to trigger the SSR heater for the set amount of time each sample cycle. 

I think desired output for the MV would be at high deviation under the setpoint that my power output would be 100 percent while lowering when approaching setpoint. But what I don't understand is how I would either guarantee that the values for the MV stay within that range.  Is it the case that I should just tune the PID to output sensible values but not worry too much if MV is in the 0-100 range and then anytime my MV is above 100 just output 100% on the SSR and vice versa for MV under 0?

Or am I just approaching this the completely wrong way?

Thank you in advance

 P.S

Currently my PID function block has the Integral and differential actions set to 0. I am experimenting with the standard PID function block

PID.thumb.jpg.c395311f99c916f4c7abb20eac

with the proportional gain to see the relationship between deviation from setpoint and the proportional gain, What I don't understand is why when my deviation from set point is 13, the proportional gain is set to 1000% then I am seeing an MV of 130, rather than 13000 is there something I am missing about what the proportional gain actually represents.

 

 

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