Inverters generate harmonics during operation, which can cause interference problems in systems or instruments located near the inverter. Interference-induced faults include: instruments producing large measurement errors, some instruments even failing to work properly, and even causing system malfunctions.
Frequency converters generate high-power harmonics, and their interference paths are similar to those of general electromagnetic interference, namely, interference voltage or current generated through circuit coupling, electromagnetic radiation, and inductive coupling. Observations have revealed that strong electromagnetic fields and power supply fluctuations are the most significant sources of interference affecting frequency converter instruments.
However, not all interference or malfunctions in instruments and meters are due to interference generated by the frequency converter. To resolve these questions and problems, we can follow these steps: When interference occurs, stop the frequency converter. If the instrument and system immediately return to normal, it can be confirmed that the interference was caused by the frequency converter, and appropriate measures should be taken.
Experts believe that the following measures can be taken at the scene of an interference fault to overcome the interference caused by the frequency converter to the instruments:
1. Add a filter circuit to the instrument circuit to block or bypass interference signals.
2. When the instrument has a digital filtering function, a certain time constant can be set to suppress interference.
3. The signal cable is a shielded cable, and the shielding layer is grounded at a single point.
4. Connect a 4.7 μF/100V capacitor in parallel to the transmitter's output signal terminal or connect a capacitor in parallel to ground on the output signal line.
5. The negative terminal of the signal line must be grounded.
6. Use a signal isolator.
