1. How to adjust the frequency of a frequency converter?
For a frequency converter to operate normally, it must meet two basic conditions: a frequency signal and an operating signal. Let's talk about the first condition, which is the frequency signal of the frequency converter.
The purpose of using a frequency converter is to change the speed of the motor by changing the output frequency of the converter. So how do we adjust the output frequency of the frequency converter? The key is to change the frequency signal provided by the frequency converter, which is called the "frequency setpoint signal". The frequency signal can be obtained from the following sources:
1. Frequency Setting via Operator Panel: Frequency setting via the operator panel is the simplest method for frequency converters. Users can directly change the set frequency using the potentiometer, numeric keys, or up/down keys on the operator panel. The biggest advantage of operator panel setting is its simplicity and convenience, while also providing monitoring functionality, displaying real-time data such as current, voltage, and speed during inverter operation.
If you choose to input a digital signal using the keyboard numeric keys or the up and down keys, the accuracy and resolution are very high because it is a digital input. If you choose to input a digital signal using the potentiometer on the control panel, the accuracy is slightly lower, but it is very practical because it does not require additional wiring like an external potentiometer for analog input.
2. External potentiometer setting refers to adjusting the frequency by using a potentiometer input from outside the frequency converter.
3. Multi-function input terminals: The set frequency value of the frequency converter is changed through the multi-function input terminals. These terminals can be connected to external buttons, PLCs, or relay output points. Through function settings, two or more of the frequency converter's function input terminals can be used for frequency setting.
II. How to measure the output voltage of a frequency converter
There are two methods for measuring the output voltage of a frequency converter: one is to measure directly with a multimeter. Set the multimeter's range to the appropriate value, connect the red clip of the multimeter to the output terminal of the frequency converter, connect the black clip to the negative terminal of the frequency converter, and then read the value on the multimeter. The other method is to measure with a digital voltmeter. Set the voltmeter's range to the appropriate value, connect the red clip of the digital voltmeter to the output terminal of the frequency converter, connect the black clip to the negative terminal of the frequency converter, and then read the value on the digital voltmeter.
The output voltage of frequency converters is often a PWM square wave, which cannot be measured by ordinary detection methods and is difficult to measure accurately with ordinary meters. However, the current waveform, having passed through the motor, acts as a good low-pass filter, and its waveform is essentially sinusoidal (though with significant distortion). It can be measured using ordinary meters.
For voltage, since the output is an I-WM waveform, accurate measurement is difficult even with RMS detector-type instruments. For current, it can be measured directly with RMS detector-type instruments without a low-pass filter, or it can be measured using a series of low-pass filters. Power and reactive time are relatively difficult to measure because the introduction of filters introduces additional phase shifts, resulting in only coarse measurements even with precise measurements.
