CWT Ultra-mini

The CWT range has been used in a wide variety of EMC applications. It has a wide-bandwidth from sub Hz into the MHz range and configurable current ranges from less than 1A to >100kA.

Two examples demonstrate the versatility:

• The CWT has been used as the reference measurement in EMC magnetic impulse immunity testing where the DUT has to continue operation in the presence of a local impulse for several kA
• The CWT has also been used in many EMC traction applications where a measurement of mA level currents at frequencies > 1kHz need to be resolved in the presence of large 16.6 or 50/60Hz currents.

The double pulse test is widely used to test the parameters of power MOSFETs and power IGBT’s. The circuit replicates the type of inductive load that is typical in power converter design. The test can be used to measure the semiconductor energy loss during switch on/off as well as the reverse recovery time of the diode.

The CWTMini50HF is the perfect choice for measuring the current flowing in modern power devices including SiC semiconductors. The 50MHz bandwidth is sufficient to measure a rise time of 12ns without distortion and the measurement delay is predictable and repeatable, which enables the user to correctly de-skew the current measurement and calculate energy loss.

The coil contains no magnetic materials and has a small cross section which minimises the inductance inserted in the primary circuit which could negatively affect the maximum achievable switching speed of the device being tested.

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, whereas probes based on magnetic materials such as hall effect become increasingly bulky and expensive at larger current ratings. 

Over a 1000A range there really is no better alternative to a PEM Rogowski current probe.

Rogowski current probes do not measure the DC component of a current. However unlike a current transformer or a fluxgate 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.

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

The CWT range is non-intrusive injecting only a few pH into the primary circuit, it has a high frequency bandwidth of up to 50MHz,  a predictable known measurement delay, versions to mitigate interference from fast voltage transients, and comes in a variety of thin and clip-around coils with different isolation voltages, making it easy to insert into even difficult to reach parts of the circuit.