Symbol and connections

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There are 4 connections available on the PI controller.

1. The input (shown through the arrow figure on the left-hand side).

   1. Any signal that you wish to be controlled, either measured or calculated

2. The output (shown on the other, so right-hand side).

   1. Valve setting, pump modulation, …

3. The set point on the topside

   1. The set point to the controller will calculate towards

4. The activation is on the bottom side.

   1. Connection to (de)-activate the controller. you can find more information on this topic further on this page.

Example connection

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In this image, you can see a simple connection of the PI controller. The controller varies the opening of the 3-way valve to lower the supply temperature into the underfloor heating loop to 35°C, by mixing in cold return.

1. The controller measures the current supply temperature (through the sensor)

2. The controller calculates the fault compared to the setpoint (Constant: 35)

3. The controller calculates the needed output (3-way valve setting) to set the supply temperature to 35°C.

Deactivate the controllers

It may be the case that the control you have set, has to be disabled or overruled at certain operating conditions (a holiday period, external override, …). Sometimes this is done in this example:

The output of the PI controller is multiplied with an overruling signal (in this case a “constant:0”, but this can be any input which gives a “0” or “1”. If the value is “0”, the valve will close as the output of the multiplier is “0”, regardless of the output of the PI controller.

This may look like a very easy solution, there is however a problem with this practice. Although the PI controller is successfully overruled, the PI controller itself will still continuously execute its “I action” and keep integrating the error over time. When the override gets set to “1”, the output of the PI controller may result in temporary, unexpected and undesired behaviour. For example unstable and overshooting output values.

Therefore, use the de-activation control signal on the PI controller itself, which will de-active the error integration itself. Note that this signal is optional and activated by default.