How to Select PID Tuning Terms and Algorithms

Setting the Control Loop Type and Gains

Alicat controllers come equipped with two different tuning algorithms: PDF and PD²I tuning.  Every controller is custom tuned at the factory for your application, or given generic terms when the application is unknown.  If your device isn’t controlling as expected, perhaps ringing around the setpoint or taking a long time to reach the setpoint, this can easily be adjusted with the tuning parameters.

See below for instructions on how to change between the two different algorithms (aka “loop types”) and change the individual gain values.

Video

 

Step-by-Step Instructions

  1. Press the bottom right button for “MENU” selection.
  2. Press the top left button for “CONTROL” selection.
  3. Press the bottom middle button for “ADV CONTROL” selection.
  4. Press the top right button for “LOOP SETUP” selection.
  5. Press the top middle button for “LOOP TYPE” selection.
  6. Use the up and down buttons to select the desired control algorithm.
  7. Press the bottom right button to “SET” this loop type.
  1. Press the bottom right button for “MENU” selection.
  2. Press the top left button for “CONTROL” selection.
  3. Press the bottom middle button for “ADV CONTROL” selection.
  4. Press the top right button for “LOOP SETUP” selection.
  5. Press the top right button for “LOOP GAINS” selection.
  6. Select the desired gain to change
    1. Top left button for P gain.
    2. Top middle button for I gain. (Not visible when PDF is selected).
    3. Top right button for D gain.
  7. Use the up, down, and select digit buttons to set your desired gain value.
  8. Press the bottom right button for “SET” selection.

“Hello, my name is Michael Whiteside, I am an application engineer here at Alicat Scientific. In this video, I’m going to show you how to adjust your PID tuning using the front display of an Alicat device. Now let’s get started.

In order to adjust the PID tuning, we will hit menu (bottom right button), control (top left button), advanced control (bottom middle button), loop setup (top right button), and first we will look at the loop type (top middle button).

Now PD/PDF control is typically used for single valve controllers while PD2I control is used for dual valve controllers and very fine tuning. We will select PD/PDF for now (bottom right button for ‘set’).

Going into the gains follows the same route, menu (bottom right button), control (top left button), advanced control (bottom middle button), loop setup (top right button), and now loop gains (top right button).

We can adjust these P and D values to whatever we would like to. Say we want to change P (top left button) to 50 (top three buttons for ‘up’, ‘down’, and ‘select digit’), hit set (bottom right button), and D (top right button) to 10,000 (top three buttons for ‘up’, ‘down’, and ‘select digit’), and hit set (bottom right button).

That is how you properly adjust the PID tuning on an Alicat device.”

What values are best for P, I, and D?

Short Answer:  It depends on your specific operating parameters and which Alicat device you’re using.

Long Answer:  If you are ordering a new Alicat, or sending one in for recalibration, we can do all the tuning for you at the factory.  Just let us know your operating conditions, and we’ll take care of the rest.  If your do need to change the gain values, there’s some tips in the links below on what values to start with and how to fine tune for each tuning algorithm.

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