FCU - Default Application - The second heating stage

This document presents the method of controlling the second heating stage in iSMA-B-FCU in analog and digital mode for fan coil units.

The dedicated output in iSMA-B-FCU for connecting an additional heater is the O4 output. The second level of heating can be activated by switching the 'DIP switch' 2 to the 'ON' position.

Picture 1. Diagram of connecting an additional heating device.

1. Digital mode

In this mode, the algorithm of the default application works with two outputs, exposing them to a PWM signal. In this configuration, we have two outputs TO1 and O4 at our disposal, the A1 output is turned off by default. The principle of operation is similar to the operation of the first heating stage, except that the second stage works with an offset and is activated when one heater does not have enough energy to heat the room or the set temperature must be reached quicker.

For additional knowledge about the variables in which the values ​​are stored and how the algorithm is calculated, open the 'iSMA-B-FCU_Application_Manual' manual on page 18 available on our website https://support.ismacontrolli.com.

2. Analog mode

In this mode, the output value is calculated in the range of 0 - 100% through the PI controller included in the default iSMA-B-FCU application. There are three outputs A1 or TO1 and a dedicated output for the second heating stage O4.

For additional knowledge about the variables in which the values ​​are stored and how the algorithm is calculated, open the 'iSMA-B-FCU_Application_Manual_V1.3' manual, page 19 available at our website https://support.ismacontrolli.com.