Accordingly, in the latter case the system must not be put into operation during the measurement. The most common clamp meters are current clamps for alternating current. The basic principle is as follows: along each electrical conductor through which a current flows, a magnetic field is generated linearly to the flowing current. The advanced clamp meter PCE-CM 5 determines the strength of this magnetic field with the help of a kind of transformer and can thus determine the current strength of alternating currents indirectly and very precisely. In addition, the meter's "Not Connected Voltage" function indicates by means of an optical signal whether or not a voltage is present on a line. Again, no measurement preparation is necessary during operation. The risk of electric shock is reduced to a minimum by this further special feature of the clamp meter.
PCE Instruments says the PCE-CM 5 is a fork-type clamp meter and stands out by its unusual design with an open fork. It thus enables simple, fast measurements on conductors. As it has no moving parts, this type of current clamp meter is less sensitive to contamination and mechanical defects than others. Click here for the full release.
More information can be found here:
https://www.pce-instruments.com/english/measuring-instruments/test-meters/clamp-meter-kat_40102.htm