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What is a control signal?

A control signal is typically used to control an electronic device. This can be a fan speed controller, a damper actuator, an EC fan, etc.
An example: Telling a fan speed controller what the desired fan speed is. By turning a knob, you can adjust the desired fan speed. What actually happens is that by turning the knob you generate a control signal (typically 0-10 Volt). In this example, 0 Volt means "Run the motor at minimum speed" and 10 Volt means "Run the motor at maximum speed".

Types of control signals
There are many different control signals. You can compare it to different languages with which people communicate. A control signal can be analogue or digital. Some examples of analogue control signals are:
   -  0-10 Volt 
   -  0-20 mA 
   -   PWM
   -   etc.

These all have their advantages and disadvantages. A 0-10 Volt signal is widely used. It is widely known and fairly easy to use. A disadvantage is that the cable length must be limited to guarantee proper operation. It is also quite susceptible to interference. Power cables in close proximity to cables with 0-10 Volt control signals are a typical source of random problems. PWM or pulse width modulation control signals are less susceptible to interference, but slightly more complex to implement. Here, too, the cable length must be limited.

Nowadays more use is made of digital control signals. An example of this is Modbus RTU communication. The big advantage of this technology is that it is robust and insensitive to interference. Cable lengths of up to 1.000 m are no problem. By using repeaters, extra segments of 1.000 m each can be added. Which control signal is used is in many cases determined by the devices with which to communicate and the possibilities they offer.

How to generate a control signal?
A control signal can be generated manually or automatically. By turning the knob of a potentiometer, you can manually generate a control signal. By turning the knob from low to high position, the control signal will increase from 0 Volt to 10 Volt. In this way you can manually set the speed of a fan. There are also control switches that split the 0-10 Volt signal into 3 or more steps. This way you can control the ventilation system in 3 positions.
A control signal can also be generated automatically. Sentera HVAC sensor controllers measure temperature, relative humidity and sometimes also CO2 or air quality. Based on these measurements, they generate a control signal. This control signal can then be used to control the fan speed.
If measurements from multiple sensors are required to control fan speed, an HVAC controller is required. This HVAC controller monitors and interprets the measurements of the various sensors. The controller's algorithm will use this information to generate a control signal and use it to control other devices (e.g. fan speed controller, damper actuator, EC fan, etc.).

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