The connection method and precautions of the external potentiometer of the inverter

Some product designs require that the potentiometer is connected to the inverter. When we operate the inverter’s external potentiometer, we should strictly follow the inverter’s instructions. This article mainly talks about the inverter’s external potentiometer connection method and the inverter substitutes the potential. Precautions for the selection of the inverter and the use of the external potentiometer of the inverter for reference.

1. Connection method of external potentiometer of frequency converter

The potentiometer is a resistance element with three lead-out pins whose resistance can be adjusted according to a certain changing law. The potentiometer is usually composed of a resistor and a movable brush. When the brush moves along the resistor body, the resistance value or voltage that has a certain relationship with the displacement is obtained at the output end.

First of all, it is recommended to use shielded wires for the wiring between the inverter and the external potentiometer. The distance between the inverter and the external potentiometer should not exceed 2 meters. When it exceeds 2 meters, the quality and wire diameter of the shielded wire should be considered. The thickness between them cannot be small. The voltage drop of the frequency converter can be ignored. If the voltage drop is too large, a single-core copper wire can be used to replace the sound shielded wire. Then the analog output of the inverter is set to the operating frequency, and then its regulator can be converted into a 4-20mA signal and sent to the signal input terminal of the inverter, so that the purpose of controlling the frequency can be achieved. At this time, the frequency of the inverter is set The setting can be set by an external frequency potentiometer. Finally, connect the sliding end of the external potentiometer to the AVI of the voltage input end of the inverter, and connect the other ends to +10V and the common end.

In addition, in theory, the potentiometer can also control two inverters at the same time, but in order to reduce the operating error, it is best to use the digital signal of two current outputs to control the potentiometer. First, set a current value (or the frequency value of the inverter). ) To the potentiometer correspondingly output two identical current values, so as to achieve the purpose of controlling two inverters at the same time. At this time, it is better to change the inverter to current signal control.

2. Precautions for the selection of the substitute potentiometer for the frequency converter

Various inverter manuals have regulations on the resistance and power of the external potentiometer. However, users sometimes cannot buy a potentiometer that meets the requirements of the manual. Therefore, the question of whether the existing potentiometer can be substituted has been raised.

For substitute potentiometers, the following principles should generally be followed:

(1) The resistance value can only be increased but not decreased. Because the resistance is small, the current of the internal control power supply of the inverter will be increased. If you don't know the internal circuit of the inverter, you should try to avoid this situation.

(2) The resistance value is too large, and the current taken by the potentiometer is too small. When the control distance is far, the anti-interference ability will be deteriorated. In addition, there is also a matching problem with the internal circuit of the inverter, so the resistance value of the potentiometer is generally not more than 10kΩ.

(3) Since the external potentiometer is adjusted frequently during the working process, the wear resistance of its internal contacts must be considered, so the power of the potentiometer should be large rather than small. Generally, it should be selected based on more than 10 times the actual power consumption. For example, if the power supply voltage is 10V and the resistance value of the potentiometer is 2kΩ, the power consumed by the potentiometer is P=U2/R=102/2000W = 1/20W, and the nominal power of the potentiometer should be selected above 1/2W.

In addition, if the resistance of the existing potentiometer is less than the specified value in the manual, the potentiometer can be connected in series with an additional resistance Ra to make Ra+RRP (RRP is the resistance of the potentiometer RP) greater than the specified value.

3. Precautions for using external potentiometer of the inverter

1. The resistance of the potentiometer should not be too large. When the inverter is controlled at a long distance, the anti-interference ability of the potentiometer will deteriorate.

2. When the external potentiometer is adjusted frequently during the working process, the operating power of the potentiometer should not be too small. Generally, it is recommended to choose 5 to 10 times the actual power loss.

3. Due to the consideration of whether the internal circuits of the inverter are matched or not, the resistance value of the selected potentiometer is generally better not to exceed 10KΩ.

4. Without knowing the internal circuit of the inverter, the resistance of the potentiometer should not be adjusted too small, because if the resistance is small, it will increase the click of the internal control power supply of the inverter, so we should pay attention to this point. .

Since the instructions of various inverters have different requirements for the resistance and power of the external potentiometer, when operating the inverter how to connect the potentiometer, you should operate according to the inverter's manual.