CWT Mini & CWT MiniHF

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  • Overview
  • Performance
  • Applications
  • Get a Quote


The CWT Mini and MiniHF are state-of-the art, clip-around, AC Rogowski current probes with a small form factor and virtually zero insertion impedance.

The New CWT MiniHF combines an innovative screened Rogowski coil providing excellent immunity to interference from fast local dV/dt transients or large 50/60Hz voltages and an extended 30MHz (-3dB) high frequency bandwidth for 100mm coils. The coil has a wide operating temperature from -40°C to +125°C and is available with 5kV peak insulation, 4.5mm thickness.

The CWT Mini features both improved high frequency and low frequency performance. The CWT Mini is available with a coil thickness of 3.5mm (2kV peak) or 4.5mm max (5kV peak).

The CWT range is ideal for power electronic applications, such as monitoring semiconductor switching waveforms or for measurements in electrically noisy environments. The easy-to-use thin, flexible, clip-around coil accurately replicates fast switching current waveforms be they sinusoidal, quasi sinusoidal or pulsed.

Standards and Approvals

  • CE marked
  • Designed and Tested to EN 61326-1:2013
  • Designed and Tested to EN 61010-1 Third Edition
  • PEM Ltd is an ISO9001:2015 registered company
  • Patents Pending


Peak current

30A peak to 120kA peak


±6.0V peak corresponding to 'Peak Current' into ≥100kΩ

±3.0V peak corresponding to 'Peak Current' into 50Ω

High Frequency Bandwidth (-3dB)

30MHz (100mm coil),  23MHz (200mm coil); CWT MiniHF

20MHz (100mm coil);  15MHz (200mm coil); CWT Mini

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℃ (CWT MiniHF -Coil and cable)

–20℃ to +100℃ (CWT Mini -Coil and cable)

Coil Lengths

100 or 200mm (custom lengths available)

Peak coil insulation (coil thickness)

2kV peak (3.5mm thickness)  *CWT Mini Only

5kV peak (4.5mm thickness)

Cable Length (coil to integrator)

1m, 2.5m or 4m (custom lengths available)

Power Supply

Option ‘B’ Battery 4 x AA (1.5V standard alkali batteries)
Plus - 2.1mm socket for 12V (±10%) DC input


Option ‘R’ Rechargeable Battery 4 x AA (1.2V NiMH batteries) with on-board trickle charge circuitry.
Plus - 2.1mm socket for 12V (±10%) DC input


  • Traceable calibration (certificate included)
  • Thin, clip-around, Rogowski coil for easy insertion into circuits with restricted access
  • Maximum coil thickness 3.5mm (2kV) or 4.5mm (5kV)
  • Non-intrusive: Loads the circuit under test by only a few pH’s
  • No magnetic materials ensures excellent linearity < 0.05% reading
  • Galvanically isolated measurement


The CWT has been supplied to major electrical engineering companies and leading research institutions around the world for the past 20 years. This versatile instrument has been used for a  wide variety of applications, some examples include:

Semiconductor Switching Waveforms

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

CWT Mini with 100mm / 2.5mm cross section coil measuring current in an IGBTThe CWT is non-intrusive injecting only a few pH into the primary circuit, wide-bandwidth greater than 10MHz, 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.

The new CWT MiniHF features an innovative screened coil making it the perfect choice for measurements on SiC devices which have faster rise times and larger blocking voltages.

Large AC Currents in Generators, Motor  Drives and Power Supplies

Unlike other forms of current measurement the size of the sense coil (the Rogowski coil) is independent of the size of the measured current. Thus for large currents the size of the Rogowski coil can be chosen to suit the conductor diameter and transducer does not require an expensive and bulky magnetic former. Over a 1000A range there really is no better alternative to the Rogowski coil.

Pulsed Power Applications

PEM’s CWT Rogowski coils have been used:

  • to monitor current in the kicker magnets in a large particle accelerator.
  • in laser power supplies
  • in a ‘Superconducting Fault Current Limiter’ (Cryogenic Application)

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
  • High frequency  Sinusoidal applications – such as Induction Heating
  • rf currents

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