CWT Ultra mini

Related Documents

Datasheet PDF file opens in a new window

 Technical Notes (HF & Rise Time)

Dimensions PDF file opens in a new window

 Power Adaptors Link to Adaptors Datasheet


  • Overview
  • Performance
  • Applications
  • Get a Quote


The CWT Ultra mini range features the smallest Rogowski coil on the market.  Maximum coil cross section of 1.7mm, small enough to fit through the legs of a TO-220 semiconductor device.

Wide bandwidth, 30MHz (-3dB) and excellent high frequency performance over a wide temperature range makes the CWT Ultra Mini ideal for measuring pulsed currents and sinusoidal waveforms in power electronic applications.

Standards and Approvals

  • CE marked
  • Designed to comply with IEC61010-1
  • PEM Ltd is an ISO9001:2015 registered company
  • Patented technology


Peak current

30A peak to 6kA peak


±6.0V peak

High Frequency Bandwidth (-3dB)


Low Frequency Bandwidth (-3dB)

Varies with model type (refer to datasheet)

Accuracy (typ.)

Calibrated to ±0.2% with conductor central in the Rogowski loop


Typical variation with conductor position ±2.0% of reading

Operating temperature range

0℃ to +40℃ (Integrator electronics)


–40℃ to +125℃ (Coil and cable)

Coil Lengths

80mm (custom lengths available)

Coil thickness

1.7mm max.

Peak coil insulation

1.2kV peak

Cable Length (coil to integrator)

1m (custom lengths available)

Power Supply

‘B’ Battery 4 x AA (1.5V standard alkali batteries)
Plus - 1.3mm socket for 12V (±10%) DC input

‘R’ Battery 4 x AA (1.2V NiMH batteries)
Plus - 1.3mm socket for 12V (±10%) DC input


Output load

≥ 100.0 kOhm (for rated accuracy, rated sensitivity)
= 50 Ohm (for rated accuracy, but half nominal sensitivity)


  • Traceable calibration (certificate included)
  • Maximum coil thickness 1.7mm
  • Non-intrusive: Loads the circuit under test by only a few pH’s
  • No magnetic materials means excellent linearity < 0.05% reading
  • Fully isolated measurement
    - Coil rated at 1.2kVpeak (withstand test is 3kVrms / 50Hz / 60 sec)


The CWT Ultra mini (CWTUM) has the smallest cross section, clip-around, Rogowski coil on the market. Combined with its wide-bandwidth the CWT ultra mini is a versatile tool for many applications particularly power electronics development work.

Switching Waveforms in Power Electronic Circuits

The CWT ultra mini can be used for a wide variety of electronic measurements such as switching loss in power semiconductors, current sharing in parallel devices or checking that in-circuit inductance is not over stressing an IGBT or MOSFET.

The CWTUM is non-intrusive injecting only a few pH into the primary circuit, wide-bandwidth 30MHz, has a predictable known measurement delay, and is thin and clip-around making it easy to insert into even difficult to reach parts of the circuit.

CWT UM measuring current in a snubber capacitorThe CWT ultra mini is small enough to measure the current in...

  • Power device bond wires
  • Load sharing in parallel TO-220 / TO-47 MOSFET devices
  • Current distribution across a semiconductor wafer
  • The connection between laminate power planes and IGBT MOSFET power modules
  • Inductor and capacitor terminals in SMPS cct’s and power converters

...making it a very useful diagnostic tool as the density of power circuits increase!

Measuring Small AC Currents in the Presence of Large DC Currents (e.g. capacitor ripple)

Rogowski current transducers do not measure the DC component of a current. However unlike a CT or hall effect device they contain no magnetic materials so are unaffected by the DC current. Therefore it is possible to use a small, flexible, Rogowski coil to measure a small AC current in the presence of a large DC current whereas a sensor based on a magnetic principle would be expensive and bulky to prevent saturation effects. One such common application is measuring the ripple current in capacitors where the main current is DC or slow time varying.

Other applications include:

  • Power converter development and diagnostics
  • Measuring hf harmonics
  • rf currents

Quote Request CWT Ultra Mini

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