Control of a three-stage fan coil by a continuous signal

Multistage fans are increasingly being replaced by continuously controlled EC motors. Nevertheless, we sometimes find ourselves in a situation where we need to control a three-stage fan of a fan coil or convector and the controller provides us with only a continuous sequence of 0...10 V to control the EC motor or VAV damper. This problem can be solved by using a multistage voltage relay.

It is more advantageous to prefer configurable types, such as Sontay IO-RM or Axio AX-RM3M - they allow jumpers to be used to set switching logic, ranges, and sometimes time parameters. Titan offers simpler functions.

It is always necessary to check whether the respective converter really works in such a way that only one relay is active at a time and the safety delay of min. 0.1 s.

The values of switching voltages for individual stages are usually chosen so that the three relays cover the entire range of 0...10 V, ie as follows:

Input voltage Active relay
4 V Stage 1
7 V Stage 2
10 V Stage 3

If the relay responds, for example, at 3 V, 6 V and 9 V, this has a minimal effect on the fan coil function, as compliance with the comfort parameters in the room is ensured by the PI sequence in the controller.

The multi-stage voltage relay can be used, for example, to control technologies in a room with Domat FCR013 and FCR015 controllers. The respective sequence has default values of 3 V, 7 V and 10 V when manually setting stages 1 to 3, but it is also possible to set the maximum and minimum sequence by parameterizing the controller, which allows the controller behavior to be adapted to the (fixed) voltage relay sequence setting.