Which analogue signals exist?
There are many different types of analogue signals, each with their own advantages and disadvantages. The device that is to be controlled by the analogue signal usually determines which signal type is required. The distance to be covered or the total cable length is also an important factor that influences the choice. In some cases, there are multiple options. These are the most commonly used analogue signals:
- Voltage signals (e.g. 0-10 Volt): These analogue signals use a different voltage or potential to transmit the information. The EC motor will detect the voltage level of the analogue signal and determine the desired motor speed based on that. This form of analogue signal is very popular because the value of the signal can easily be measured with a Voltmeter. This makes the trouble shooting much easier.
The disadvantage is that the cable length must remain limited. Due to the electrical resistance of cables, there will be a voltage drop with longer cable lengths (10 Volt at the beginning of the cable will no longer be 10 Volt at the end of the cable). This results in lower accuracy. In the example of the EC motor, it will be impossible to reach the maximum fan speed if the analogue signal cable between potentiometer and EC motor is too long. The reason is that the analogue control signal cannot reach it's maximum value of 10 Volt due to the voltage drop in the long cable. - Electrical resistance (e.g. 0 to 10 kΩ): This is the most well-known way to communicate a value in the world of electronics. By the way, a potentiometer is also an electronic component with variable resistance value - more about this later in this article. Back to our example with the EC motor. The EC motor will determine the desired motor speed based on the resistance value of the analogue signal. Here too, a longer cable length between the potentiometer and the EC motor will result in reduced accuracy due to the increasing electrical resistance of the cable. If the cable length between both devices can be kept short, this is a simple and cost-effective solution.
- Current signals (e.g. 4-20 mA): Analogue signals that vary the electrical current to communicate a value. The EC motor will determine the motor speed based on the current of the analogue signal. The more mA detected, the higher the motor speed. In this example, 20 mA corresponds with the maximum motor speed.
The big advantage here is that no accuracy is lost in case of increasing cable length. The increased electrical resistance of the cable will be compensated by the analog signal and the desired current will be achieved. A cable break can also be detected (0 mA can only occur in case of a cable break, since the minimum value of the analogue signal is 4 mA). Detecting possible errors is more complex because current is more difficult to measure than voltage. - Frequency signals (e.g. Pulse-Width Modulation or PWM): This type of analogue signal is also called a pulse train. It is a constant series of pulses with identical amplitude (voltage). The difference is in the frequency and width of the pulses. The EC motor receives a constant series of electrical pulses. The motor speed is determined based on the frequency and duration of the pulses. This form of analog signal is not sensitive to increasing electrical resistance or voltage drops due to longer cable lengths. More advanced electronics are needed to correctly interpret the pulse train and detecting possible errors is also less easy.
In the end, all these analogue signals do the same: they transmit or communicate a certain value between different devices. The difference between these analogue signal types can be seen as communicating the same message in a different language.
In a summary: Voltage signals and electrical resistance are simple and suitable for shorter distances, current and frequency signals are more complex and more suitable for longer distances.