Near field probing technique - EMI Debugging

[FreshmanNewbie]

I am reading about the near field probing using Electric field probes and Magnetic field probes.

I understand that E field probes would pickup voltage changes and the H field probes would pick up current changes. But I am not able to find when to use which probe?

Can someone tell me when to use which probe for EMI debugging? Like, If I am looking for emissions in my circuit board, for which purpose should I use which probe and when to use them?

 

[BradtheRad]

Probes that detect one while unaffected by the other. It implies the ability to sense without direct contact.

To detect current, a sensor that responds to a magnetic flux generated by current:
* Ordinary compass
* Hall effect sensor
* Wire coil

For detecting voltage without direct contact there are modern store-bought instruments. (Not sure how they work.)

Often you can pick up ambient mains hum via a length of wire feeding an input of some high-gain device. I hold the probe of my oscilloscope and see a distorted sinewave 60 Hz.

For detecting static charge (high voltage) from a distance, see this simple inexpensive project based on an fet:

Build this simple "electronic electroscope," a FET electrometer