A frequency converter, the operation panel can be controlled normally, and the adjustment frequency can also be changed from 0 to 50HZ, but with an external potentiometer, the frequency cannot be adjusted to 20HZ, what is the reason?

Analyze the reasons

The panel can adjust the frequency, but the external one cannot. It means that the inverter itself has no problem. It is necessary to check whether the external potentiometer of the inverter gives you any problems with the peripheral components or lines.

First, make sure that the potentiometer is good, and then make sure that the wiring to the inverter terminals is correct. The rest is the frequency setting of the inverter.

1. The selection of the resistance value of the potentiometer should correspond to the requirements in the manual

For the selection of the resistance value of the external potentiometer of the inverter, the analog given signal of the inverter is generally: 0~10V, 4~20ma, so when choosing the given value of the potentiometer, the following two situations should be considered:

1. Voltage signal 0~10V

When the external power supply voltage is 10V, if a potentiometer with a resistance of 10K is selected, the working current is 1mA. According to the field experience, as long as the analog signal is less than 1mA, the anti-interference ability is sufficient. Therefore, as long as the resistance of the potentiometer is less than or equal to 10K, it is fine.

If the output voltage of the inverter is 0-10V, a 10K potentiometer should be selected. If the output voltage of the inverter is 0-5V, a 4.7K potentiometer should be selected. If the current is too large, it will cause unprovoked power loss. .

2. Current signal 4~20ma

When the external input signal is 4~20ma, a 500 ohm resistor is connected in series in the circuit. Under the 10V power supply, the corresponding resistance value of 20ma is 500.

2. Check the maximum frequency setting and upper limit frequency setting of the inverter

3. Wiring

To check whether the wiring of the potentiometer pins is correct, when debugging the potentiometer, measure to see if the voltage of the potentiometer pins changes.

The fixed terminals on both sides of the potentiometer are directly connected to the 10V power supply and ground signal on the inverter terminals, and the sliding adjustable terminal in the middle of the potentiometer is connected to the analog output signal of the inverter, and then adjust the resistance of the potentiometer to see the output. whether the voltage has changed.

Fourth, the frequency signal source parameters of the inverter,

To change the frequency controlled by the panel to the frequency controlled by an external pin, the parameters are set by panel or potentiometer or voltage, current or host computer, and the set parameter values ​​are different.

5. Check the line between the potentiometer and the inverter. It may be that the power line or the shielding line is damaged, causing the line to leak or short-circuit.

The use of potentiometers has its limitations. Since the potentiometer inputs a voltage signal of 0 to 10V, the interference of the voltage signal increases with the extension of the transmission distance. If the distance between the installation site and the inverter is far, the accuracy of signal transmission cannot be guaranteed. In this case, the distance between them should be shortened as much as possible. If the distance is too long, the resistance of the potentiometer will be smaller.

Many times it is external problems that cause the inverter to work abnormally, but we are always easy to suspect that it is the problem of the inverter itself.