RF Current Probes for EMC Testing

Current Probes for EMC Testing

Current probes are also called RF current transformers. Current probes are used to sense current flowing through a conductor and convert it to a voltage that can then be viewed and measured on an oscilloscope or other test device. Current measurements are made by having the current-carrying conductor pass through the aperture of the probe and the probe’s output voltage is measured using an analyzer (or field intensity meter).

Two types of Current Probes used in EMC measurements:

1. Immunity Current Probes: Immunity Current Probes are configured to perform conducted immunity testing as per IEC 61000-4-6 standards. The current clamp is used to inject noise on to a cable in the system under test for immunity (or susceptibility).
2. Emission Current Probes: Current Emissions Probes are used for measuring conducted noise for compliance to standards such as MIL-STD-461, DO-160, CISPR, etc.

How to conduct EMC Calibrations with a current probe

1. Clamp the chosen probe over a cable.
2. Use bubble wrap or other non-conductive material to center cable in probe hole.
3. Move probe back and forth along the cable to find the maximum reading.
4. Take reading off analyzer screen in dB.
5. Calculate dBμA using: dBμA = dBμV – Transfer Impedance (dBΩ).
6. Convert dBμA to A using: 10ˆ(dBμA-120)/20. This gives you I(cm).
7. Convert V/m to dBuV/m using: 20*log(I(cm))+120.
8. Compare to the field strength limit at the noise frequency in the IEEE standard.

Key Parameters when looking for a Current Probe:

1. Frequency Range: Range of operation of the current probe.
2. Type of Probe: Immunity or Emission Current Probe.
3. Bare-Wire Voltage: It is the maximum threshold voltage a probe can withstand to avoid injury or fire. It is always advisable not to use the probe in circuits where voltage exceeds the bare wire threshold level. Always maintain adequate spacing between the housing on the probe head and other exposed circuit connections.
4. Output Sensitivity: Current probe sensitivity is a probes ability, as a transducer, to output a voltage large enough to be measured by the oscilloscope when measuring small current.
5. Primary Current: It is the current which is induced in the primary winding of a transformer and is independent of the secondary load current.
6. Transfer Impedance: The RF current (IP) in microamps in the conductor under test is determined from the reading of the current probe output in microvolts (ES) divided by the current probe.

everything RF has listed current probes that can be used for EMC testing from the leading manufacturers. The list of current probes can be narrowed down by the connector type and the peak current. View product specifications, download datasheets, and request quotes for current probes that meet your requirement.