Sensing Instrument
Inductive transducers detect the localized high-frequency magnetic fields generated by currents flowing through printed circuit board traces. A magnetic loop probe measures the voltage induced by the changing magnetic flux passing through its wire loop when held close to the board surface. This instrument is the primary sensor used in near-field scanning to identify hotspots of electromagnetic interference on a functioning assembly.
The measurement accuracy of the probe drops when the trace width is comparable to the loop diameter, because spatial averaging degrades the resolution.
Troubleshooting Scan
Troubleshooting procedures for electromagnetic compatibility use these localized measurements to trace the path of noise currents on a circuit board. When a board fails radiated emission limits, a magnetic loop probe is swept across the board surface to locate the specific trace or component that is radiating. This scan identifies high-frequency currents flowing in ground loops or returning along improper paths.
The resulting spatial map of magnetic intensity guides the placement of filters or layout modifications. The measurement must be conducted with the probe oriented correctly, since the induced voltage is proportional to the cosine of the angle between the loop axis and the magnetic field vector.
Calibration Verification
Instrument calibration ensures that the voltage measured by the probe corresponds to the actual magnetic field strength. If the probe is uncalibrated, the scan provides only relative intensity rather than quantitative field values. This step is necessary to maintain the consistency of scans between different test labs.
