1. Introduction
Power Electronic Measurements Ltd (PEM), founded in 1991 and headquartered in the United Kingdom, is a market leader in Rogowski current sensing equipment. Through more than three decades of technical accumulation and innovation, PEM products have been exported to more than 35 countries worldwide and have built an outstanding reputation in the field of power electronics measurement.
Rogowski coil technology is a current measurement method based on Faraday's law of electromagnetic induction. It measures current indirectly by detecting the rate of change of the magnetic field around a current-carrying conductor. Compared with traditional Hall sensors or current transformers, Rogowski coils offer unique advantages such as no magnetic core, no saturation, excellent linearity, wide bandwidth, and compact size, making them particularly suitable for current measurement in high-frequency, high-current, and space-constrained scenarios.
Technology Positioning
As a pioneer in Rogowski coil technology, PEM offers product lines covering the full spectrum from conventional measurement to high-frequency precision measurement, providing reliable solutions for power electronics R&D, semiconductor device testing, and industrial equipment diagnostics.
2. Core Technical Advantages
2.1 Non-Intrusive Flexible Measurement
PEM Rogowski coils use a flexible coil design with a wire diameter of only 3.5mm or 4.5mm, allowing them to be easily wrapped around irregular conductors, busbars, cable bundles, and other test objects. This non-contact measurement method has almost no impact on the circuit under test and does not introduce extra inductance or resistance, ensuring the authenticity of the measurement result. The thin coil can even be installed between the leads of TO-220 and TO-247 semiconductor packages to meet compact-space measurement requirements.
2.2 Wide Bandwidth and High-Accuracy Measurement
The CWTMini50HF series provides bandwidth up to 50MHz (-3dB) with a rise time of only 12.5ns, enabling accurate capture of fast switching waveforms from wide-bandgap semiconductor devices such as SiC and GaN. Accuracy can reach +/-0.2% when the conductor is centered in the coil, meeting precision measurement requirements. An innovative electrostatic shielding design effectively suppresses fast dV/dt transient interference, allowing clear measurement signals even in noisy environments.
2.3 No Magnetic Saturation and Wide Current Range Tolerance
Rogowski coils contain no magnetic material, completely eliminating magnetic saturation. This allows them to measure an extremely wide current range, from tens of amperes to hundreds of kiloamperes, and they will not be damaged even when the current exceeds the nominal range. Maximum di/dt tolerance reaches 70-100kA/us, making them suitable for pulse power, short-circuit testing, and other extreme operating conditions.
2.4 DC Isolation and Ripple Measurement
Because Rogowski coils operate based on electromagnetic induction, they naturally cannot measure DC current. However, this becomes a unique advantage in certain applications: they can accurately measure superimposed AC ripple current in the presence of large DC bias. For example, in DC busbars or battery charge-discharge systems, they can clearly separate the DC component from the AC ripple component.
2.5 High Insulation Withstand Voltage and Safety
The coils use high-performance insulating materials and provide 2kV or 5kV withstand voltage options, making them suitable for current measurement in high-voltage environments. Unlike current transformers, Rogowski coils do not have the risk of open-circuit danger on the secondary side, so operators can safely connect and remove the probe without concern about high-voltage kickback.
3. Typical Application Cases
The following sections cover five scenarios: SiC switching characterization, IGBT module loss measurement, large-current pulse testing, current measurement in high-voltage environments, and capacitor ripple current monitoring. The content stays as close as possible to the original material.
Case 1
SiC Power Device Switching Characterization
Focused on fast switching waveform capture, dV/dt immunity, and installation in compact spaces.
Case 2
IGBT Module Loss Measurement
Focused on high-accuracy current waveforms, transient loss calculation, and zero added loss from the measurement method.
Case 3
Large-Current Pulse Testing
Focused on ultra-wide range capability, no magnetic saturation, and very high di/dt tolerance.
Case 4
Current Measurement in High-Voltage Environments
Focused on 5kV insulation withstand capability, safe operation, and industrial-environment adaptability.
Case 5
Capacitor Ripple Current Monitoring
Focused on resolving AC ripple components under large DC bias and flexible board-level installation.
Case 1: SiC Power Device Switching Characterization
Application Background
Silicon carbide (SiC) power devices are known for high switching speed and low conduction loss, with switching frequencies reaching hundreds of kilohertz or even the megahertz range. Accurate measurement of switching waveforms is critical for device characterization, driver circuit optimization, and electromagnetic interference evaluation.
Measurement Challenges
The switching rise and fall times of SiC devices can be only a few tens of nanoseconds, which demands extremely high bandwidth from the measurement system. At the same time, the high-speed switching of the device generates strong dV/dt noise that can easily interfere with the measured signal.
PEM Solution
The CWTMini50HF series provides 50MHz bandwidth and 12.5ns rise time, enabling complete capture of SiC switching transient waveforms. The innovative electrostatically shielded Rogowski coil design effectively suppresses interference caused by fast dV/dt transients, ensuring true current waveforms even in noisy environments. The flexible coil can be wrapped around the leads of TO-247 packaged devices, making installation convenient on compact test platforms.
Solution Advantages
- High bandwidth matches the fast switching characteristics of SiC devices.
- Electrostatic shielding design provides strong anti-interference capability.
- Flexible coil adapts to compact packages and is easy to install.
Case 2: IGBT Module Loss Measurement
Application Background
IGBT modules are core power devices in frequency converters and inverters. Their switching loss and conduction loss directly affect system efficiency and thermal management design. Accurate measurement of turn-on and turn-off current waveforms is the basis for loss calculation.
Measurement Challenges
Loss measurement requires high-accuracy current waveform data, especially during turn-on and turn-off transients, where current changes rapidly and the duration is short. At the same time, the measurement device itself must not introduce extra loss or interference.
PEM Solution
The CWT Mini series provides +/-0.2% measurement accuracy to meet the requirements of precision loss measurement. Its 30MHz bandwidth clearly records IGBT turn-on and turn-off current waveforms, and when combined with voltage measurement data, switching losses can be calculated accurately. Because the Rogowski coil has no magnetic core, there is no hysteresis loss, and it does not affect the loss distribution of the circuit under test.
Solution Advantages
- High-accuracy measurement supports precise loss calculation.
- Wide bandwidth captures complete switching transient waveforms.
- No magnetic core avoids introducing extra loss.
Case 3: Large-Current Pulse Testing
Application Background
Applications such as pulse power systems, circuit breaker testing, and arc welding involve large current pulses whose peaks can reach tens of kiloamperes or more. Such testing requires measurement equipment that can withstand extreme current without damage.
Measurement Challenges
Traditional current sensors may saturate, distort, or even be damaged when the current exceeds their range. The rise rate of large current pulses is extremely fast, placing very high demands on the di/dt tolerance of the measurement device.
PEM Solution
Rogowski coils contain no magnetic material, so there is no magnetic saturation. Even when current far exceeds the nominal range, the probe will not be damaged. The CWT Mini series can measure peak current up to 300kA with di/dt tolerance of 70-100kA/us, making it suitable for large-current pulse testing. The flexible coil can be wrapped around thick busbars or multiple parallel cables for easy installation.
Solution Advantages
- No magnetic saturation design supports wide current range without damage.
- Very high di/dt tolerance suits fast pulse conditions.
- Flexible coil adapts to large conductors.
Case 4: Current Measurement in High-Voltage Environments
Application Background
In systems such as high-voltage frequency converters, power electronic transformers, and HVDC transmission, power devices and busbars operate at voltage levels of several kilovolts. Measuring current in such environments requires sufficient insulation withstand capability.
Measurement Challenges
In high-voltage environments, the probe must have reliable insulation performance, and operator safety is also a critical consideration. Traditional Hall sensors often struggle to meet high-voltage insulation requirements.
PEM Solution
PEM offers coil options with 4.5mm diameter and 5kV withstand voltage for current measurement in high-voltage environments. Rogowski coils do not present open-secondary hazards, allowing operators to connect and remove the probe safely. The coils can operate within a temperature range of -40 degrees C to +125 degrees C, adapting well to harsh industrial environments.
Solution Advantages
- 5kV insulation withstand capability satisfies high-voltage application needs.
- No open-secondary hazard improves operational safety.
- Wide operating temperature range suits harsh environments.
Case 5: Capacitor Ripple Current Monitoring
Application Background
Electrolytic capacitors and film capacitors perform filtering and energy storage functions in power electronic systems, and ripple current directly affects capacitor lifetime. In DC bus or battery systems, capacitor ripple current is superimposed on the DC component.
Measurement Challenges
Traditional current sensors are prone to saturation in the presence of large DC bias, making it difficult to measure the superimposed AC ripple accurately. In addition, ripple current often contains high-frequency components, so the measurement device needs sufficient bandwidth.
PEM Solution
Rogowski coils naturally isolate the DC component and can directly measure AC ripple superimposed on large DC current. The 30MHz bandwidth of the CWT Mini series covers high-frequency ripple components and helps engineers evaluate capacitor operating conditions more comprehensively. The flexible coil can be wrapped around capacitor leads or connection wires, enabling convenient measurement at board level.
Solution Advantages
- Naturally isolates DC and focuses on AC ripple measurement.
- Wide bandwidth covers high-frequency ripple components.
- Flexible design supports easy board-level installation.
4. Summary
With core technical advantages such as no magnetic core, no saturation, wide bandwidth, high accuracy, and flexible installation, PEM flexible current probes (Rogowski coils) demonstrate unique application value in the field of power electronics measurement. From high-speed switching testing of wide-bandgap semiconductors such as SiC and GaN, to precision loss measurement of IGBT modules, from high di/dt tolerance in large-current pulse testing, to safe measurement in high-voltage environments, and then to ripple current monitoring in DC systems, the PEM product family covers a wide range of engineering applications.
Its innovative electrostatic shielding design, traceable calibration data, and wide operating temperature range further enhance product reliability and professionalism. For power electronics R&D engineers and test engineers, PEM Rogowski coils are powerful tools for solving complex current measurement challenges and provide strong technical support for device characterization, system diagnosis, and product verification.
