The output frequency of a frequency inverter refers to the actual value during operation, which often differs slightly from the given frequency signal. It needs to be measured for reference to facilitate feedback adjustment. If the difference is significant, the given signal source, load motor and other devices should be inspected.

There are many methods to detect the actual output frequency of the inverter. The common ones are using the analog output signal of the inverter and communication methods.

1. Analog method. As we know, frequency inverters are equipped with analog input and output terminals. The analog input is used for frequency reference, such as 0–10 V DC voltage signals and 0–20 mA current signals. The analog output is used to monitor the inverter’s operating status; operating voltage, operating current, power, and the frequency value we need to detect can all be output in analog form. These outputs are also available as voltage or current signals, and the output parameters can be selected in the inverter settings. Common detection devices include:

1：Direct measurement with ammeters and voltmeters, calculating the actual operating frequency based on the displayed values.

2：Digital displays such as tachometers, which convert analog signals into digital values for easier reading.

3：AD modules connected to a PLC, which collect analog signals, convert them into digital values, and perform feedback control.

In fact, they all share the same principle: converting the analog signal into the actual frequency value. For example, a 10 V signal corresponds to the maximum frequency of 50 Hz. The frequency can be calculated proportionally. For instance, a 2.5 V signal corresponds to an inverter output frequency of 12.5 Hz.

2. Communication method. This method is relatively more difficult in terms of technology, but the wiring is simpler, and data acquisition is convenient without conversion. Nowadays, almost all frequency inverters support communication control. We can not only use it to control the inverter operation, such as frequency setting, forward and reverse rotation, but also collect real‑time operating status. All data transmission and reception are completed through just a few cables, and operation only requires sending corresponding commands.

Common communication methods include MODBUS, which is available in most economical and general‑purpose inverters. Some medium-to-large, high-performance inverters are also equipped with PROFIBUS, PROFINET, ETHERCAT communication, etc. We can directly use these communication methods to acquire the operating frequency. The specific method depends on the supported communication format of the inverter and the host computer.