current sensing probe (CSP)
Currents can be measured by breaking the current-carrying conductor circuit into which the ammeter is then connected, or inductively by measuring the magnetic field that forms around the current-carrying conductor. For the latter measurement there are current clamps, which are led around the current-carrying conductor.
Current clamps are measuring transducers that work according to the transformer principle. The current clamp core is ring-shaped and consists of an iron core. The transformer-like toroidal core can be opened to accommodate the current-carrying conductor. Depending on the diameter of the current clamp core, several conductors or busbars can also be enclosed by the current clamp.
An alternating current generates an induction voltage in the current clamp core, which is picked up via a secondary winding and fed to the measuring device.
Current clamps are only suitable for AC current measurements, in particular for measuring high currents of up to several kilo-amperes (kA). Since current clamps are generally used in low-voltage technology, their frequency range is in the range of the mains frequency. This is where they have their highest accuracy when measuring rms values. A significant advantage of current clamps is that they are potential-free, since there is no connection between the current clamp core and the current-carrying conductor. This means that the voltage of the current-carrying conductor can also be several hundred volts or even kilovolts (kV).
However, alternating fields only occur with alternating voltage. This means that current clamps based on the transformer principle can only measure alternating currents, but not direct currents. Therefore, current clamps are additionally equipped with Hall sensors or magnetic field sensors for DC current measurement.