Rohde & Schwarz CMN50HF15 probe, Rogowski Current Probe, 3 Hz to 50 MHz, 3 kA

Description

Power module work often needs one probe for the fast edge and the fault current alike. The Rohde & Schwarz CMN50HF15 probe belongs to the Rogowski family of current probes. In other words, it pairs a flexible air-core coil with an integrator that outputs a voltage in step with the current. It spans 3.0 Hz to 50 MHz and up to 3 kA. Lost in HCM supplies it in Vietnam for rental or purchase.

The middle of the CMN50HF range

Rohde & Schwarz lists three CMN50HF coils with a 2.5 m cable: 600 A, 3 kA and 6 kA. This one sits between them. Its output is 2 mV/A, so a 500 A pulse appears as 1 V at the scope. That level is easy to read, while the range still leaves room for fault events. Rohde & Schwarz also lists the long code CWTMini50HF/15 for this coil.

Jobs on the power test floor

• Double-pulse tests on IGBT and SiC modules.
• Phase currents in EV traction inverters.
• Capacitor discharge and pulse circuits.
• Tight gaps between leads where a clamp jaw will not fit.

The thin 100 mm coil helps in that last case. In addition, the coil does not load the circuit the way a shunt would, because nothing goes in series with the conductor.

Setting up the Rohde & Schwarz CMN50HF15 probe

• First, inspect the coil and cable for cuts or kinks.
• Next, loop the coil around one conductor and close it.
• Then enter 2 mV/A as the channel scale on the scope.
• Check the termination the R&S manual asks for.
• Finally, deskew against your voltage probe before you compute power.

Rent it or own it

A module qualification run may last only a few weeks, so renting is often enough. On the other hand, a lab that tests every new design may want to buy. Either way, ask Lost in HCM for a quote and list the scope model, current levels, coil size needs and dates. Compare more oscilloscope probes on this site, or check the Rohde & Schwarz probe overview. For anything else, contact SMK Vietnam.

Questions about the CMN50HF15

Why pick 3 kA rather than 6 kA?

The 3 kA coil gives twice the output per amp, 2 mV/A against 1 mV/A. So moderate currents stand taller on the screen.

How low in frequency does it reach?

The listing gives 3.0 Hz. Below that, and at DC, a Rogowski coil gives no useful output.

Does the Rohde & Schwarz CMN50HF15 probe need a special scope?

No scope model is named. The probe needs an input that suits its output, so confirm termination and scaling first.