Control signals

What is a control signal?

Control signals are typically used to control devices remotely. We distinguish between digital and analogue control signals. Although analogue signals have been popular for many years, the HVAC market starts to discover the advantages of digital control signals.

Type of signals

Digital communication

Digital communication (e.g. Modbus RTU) offers many advantages. Cable lengths up to 1.000 m are possible. Not only is the requested fan speed transmitted to the motor or fan speed controller but also it is also possible to receive information. Motor status, motor speed, motor temperature, actual motor power, etc. can be monitored on a continuous basis. Since Modbus RTU is an open communication protocol, most HVAC devices with Modbus RTU communication can exchange information. Via the Sentera internet gateway, they can be connected to SenteraWeb – the online platform of Sentera. This universal online HVAC platform makes it possible to monitor connected HVAC devices, to adjust settings and to log data.

Analogue control

Analogue control signals have been popular in the (home) automation industry for many years. Via a simple 0-10V signal, the requested fan speed is transmitted to the EC fan or fan speed controller. Even today, many EC fans are controlled via a 0-10V signal. It is a simple technology that works fine if cable lengths remain limited. However, if the control lines are installed nearby power lines, there is a risk of interferences. It is advisable to keep the cable length of the analogue control signal limited to maximum 10 m and to use shielded cables to minimise the risk of interferences.

Type of controllers

Control switch for 3-step fan speed control

To adjust fan speed in 3 steps, a control switch can be used. Control switches generate a 0-10V signal in 3 steps. They are available with or without OFF position.

Their stepped 0-10V signal can be used to control EC fan, AC fan speed controllers, frequency inverters, etc. Position 1 and position 2 can be adjusted via internal trimmers. Position 3 is equal to the supplied voltage – typical 10 VDC. In case there is an off position, this corresponds to 0 VDC.

Potentiometers for variable fan speed control

A potentiometer generates a 0-10 V control signal. This control signal can be used for a continuously variable EC fan speed control. It can also control a frequency inverter, an AC fan speed controller, etc. Some potentiometers generate other analogue control signals, e.g. 0-20 mA or a PWM signal. Potentiometers are available with different supply voltages and with or without off position.

HVAC sensors for demand based fan speed control

Intelligent HVAC sensors generate a 0-10V control signal based on the measurements. They can directly control EC fan speed, AC fan speed controllers or frequency inverters. The fan speed is automatically controlled to keep temperature, relative humidity, CO₂, TVOC or differential pressure within the selected range. All parameters can be adjusted via Modbus RTU.