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Showing content with the highest reputation on 02/07/2020 in all areas

  1. 1 point
    First you need to scale your analog input that you have your RTD connected to. What are the specs on your RTD transmitter? From the -T20 specifications: You've mapped MI 0 to Analog Input 0. So at 4 mA MI 0 will return 204, and at 20 mA it will read 1023, which is the output from the 10 bit A/D converter. You need to know what real temperatures that corresponds to and us a LINEAR block to do the scaling before you feed it into the PID block. Read the Help on how this block works. A common spec for an RTD transmitter is 4/20 mA = 0 - 250 C. Here's how the LINEAR block should look for this scaling: The PID CONFIG block should only be called once at startup, and the input should be the scaled temperature: You have to put values in the input parameters before the PID block will function. You can use the power-up values to eliminate setting them with the program. Now the big question - do you know how PID works? The output of the block will be an analog value that will span between the Control Value high and low limits. I put some in for you, but if you don't understand what they mean you need to spend some time reading ALL the Help on the block. You'll probably have to convert the output to some kind of time proportional signal to drive a discrete output. You'll also have to run Auto-Tune or set the P, I, and D parameters manually while it's running. Joe T. Termotunel JT.vlp
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