How to measure the output frequency of the inverter?

The output frequency of the inverter refers to the value during actual operation, which is often slightly different from the given frequency signal. It needs to be measured for our reference to facilitate feedback adjustment. If the difference is large, the given source and load motor and other devices need to be detected. How to detect the actual output frequency of the inverter? There are many methods. The most common one is to use the analog output signal of the inverter and the communication method.

1. Analog method

We all know that the inverter has analog input and output parts, where analog input is used for frequency setting, such as 0-10v DC voltage signal and 0-20ma current signal; analog output is to detect the operating status of the inverter, such as operating voltage, operating current, power and the frequency value we want to detect can be given in the form of analog quantity. The same output forms include voltage signal and current signal. We can select this output parameter in the inverter settings. Common detection devices are:

(1) Ammeter and voltmeter directly measure and calculate the actual operating frequency based on the table value

(2) Digital display such as tachometer converts analog quantity into digital quantity for display, which is more convenient

(3) AD module and PLC collect analog quantity and convert it into digital quantity for feedback control

In fact, their principles are the same, that is, converting analog quantity into actual frequency value, such as 10V voltage signal corresponds to the maximum value of 50Hz, and it can be converted according to the proportional relationship. For example, 2.5V corresponds to the inverter output frequency of 12.5Hz.

2. Communication method

This is relatively difficult, but the wiring is relatively simple and the value collection is more convenient without conversion. Nowadays, inverters basically support communication control. We can not only use it to control the operation of the inverter, such as frequency setting, forward and reverse rotation, but also collect the operation status in real time. All data transmission and reception are completed through a few cables, and the operation is also to send the corresponding command.

Common communication methods include MODBUS, which is available in economical and general-purpose inverters. Some medium-sized and large-scale, high-performance inverters also have PROFIBUS communication, PROFINET communication, ETHERCAT communication, etc. We can directly use these communication methods to complete the collection of operating frequency. The specific method depends on the communication format supported by the inverter and the host computer.