Many people currently use external potentiometers to connect frequency converters. Frequency setting is simple and convenient; just turn the knob of the external potentiometer to set the frequency. So, do you know how to connect a potentiometer to a frequency converter? What are the precautions for using an external potentiometer with a frequency converter? Since the resistance and power specifications for external potentiometers vary depending on the frequency converter, you should follow the frequency converter's instruction manual when connecting an external potentiometer to the frequency converter.
Potentiometer principle
A potentiometer is a resistive element with three leads whose resistance can be adjusted according to a certain rule. A potentiometer typically consists of a resistive element and a movable brush. When the brush moves along the resistive element, a resistance value or voltage, which is proportional to the displacement, is obtained at the output terminal.
How do you connect a potentiometer to a frequency converter?
First, shielded cables should be used for wiring between the frequency converter and the external potentiometer. The distance between the frequency converter and the external potentiometer should ideally not exceed 2 meters. If it exceeds 2 meters, the quality of the shielding cable must be considered, and the thickness of the wire should not be too small. The voltage drop across the frequency converter is negligible. If the voltage drop is too large, a single-core copper wire shielded cable can be used instead of a dedicated shielded cable. Next, set the analog input of the frequency converter to the operating frequency. Then, convert the analog input to a 4-20mA signal and send it to the signal input terminal of the frequency converter. This achieves the purpose of frequency control. The frequency of the frequency converter can be set using an external frequency potentiometer. Finally, connect the sliding terminal of the external potentiometer to the AVI terminal of the frequency converter's voltage input, and connect the other two terminals to +10V and the common terminal.
In theory, a potentiometer can control two frequency converters simultaneously. However, to reduce operational errors, it's best to use two digital current output signals to control the potentiometer. First, set a current value (or the frequency value of the frequency converter) and assign two identical current values to the potentiometer's outputs. This is the only way to achieve simultaneous control of two frequency converters. In this case, it's best to change the frequency converter to current signal control.
The potentiometer on the frequency converter, used for external speed setting, achieves a 0V to 10V input change through the variation of its own voltage divider resistor. The potentiometer has two terminals: one connected to the reference voltage of 10V, and the other connected to 0V. The remaining signal line is connected to the AI input port.
Precautions for using external potentiometers for frequency converters
1. The resistance of the potentiometer should not be too large, as this will reduce the potentiometer's anti-interference capability when controlling the frequency converter at a long distance.
2. When the external potentiometer is adjusted frequently during operation, its operating power should not be too small. It is generally recommended to select one with a power consumption of 5 to 10 times or more than the actual power loss.
3. Considering the compatibility of the internal circuits of the frequency converter, the resistance value of the selected potentiometer should generally not exceed 10KΩ.
4. Without understanding the internal circuitry of the frequency converter, the potentiometer resistance should not be adjusted too low, as a low resistance will increase the power consumption of the internal control power supply of the frequency converter. Therefore, this point should be noted.
Potentiometer connected to frequency converter, frequency converter settings
First, connect the electric potentiometer to the power supply, which is usually 0~10V. Generally, you can directly use the 10V power supply on the frequency converter, usually called Vref and GND.
Connect the voltage output of the electric potentiometer to the corresponding AI terminal. Note the type of AI selected; it must be a -10V to 10V voltage input terminal. Some inverters, such as certain ABB models, have fixed voltage AI terminals and cannot be switched between current and voltage. Some inverters, such as the ABB ACS880 series, allow switching; you can use jumpers and parameters to set the AI to voltage. Note that the parameters and jumpers must be set consistently; otherwise, a fault will occur.
Set the AI range, for example, select 0~10V.
Set the speed corresponding to 0V.
Set the speed corresponding to 10V.
Set the speed setpoint parameter to the AI of the wiring.
Configure other relevant alarms and parameters, such as filtering.
