Oscilloscope News

PEM CMC03 May 2016 - Power Electronic Measurements (PEM) Ltd launched new non-contact current probes for measuring HF common mode currents in Variable Frequency Drives (VSDs) used to control AC motors. The new CMC series of current probes, using Rogowski technology, empower engineers to assess the magnitude of the threat posed by HF common-mode currents, that can damage motor bearings and interfere with nearby electrical equipment.

The current measurements can help determine suitable corrective action, such as fitting brushes, insulated bearings, or choke coils, and with further measurements assess the effectiveness of the chosen remedy.

The screened coils have excellent immunity to voltage disturbances and a low frequency (-3dB) bandwidth that attenuates unwanted 50/60Hz magnetic fields while maximising the SNR of the measurement of the high frequency common mode currents. Available in coil sizes from 300 to 1000mm, and longer if required, making them ideal for use with a wide range of motor shafts. Even with a coil circumference of 1000mm the CMC probes can achieve a high frequency (-3dB) >10MHz.

The probes are available in three sensitivity grades for measuring bearing currents up to 37.5A, 75A or 150A peak. The peak detected current corresponds to a maximum output voltage of ±7.5V when connected to an oscilloscope input via the BNC output provided.