Clamp Meter (or Clamp on meter) is a current transformer device to measure the high values of currents without disturbing (interrupting) the circuit.
Special features of Clamp Meter
Clamp Meter can be used instantaneously for the measurement of current with no physical connection with the HV circuits. It is portable and used in HV or LV line current measurements. Its core can be opened (split) with strigger switch to accommodate the cable, wire, bus bar, fuse link etc. for current measurement.
Construction & Working of Clamp Meter
Figure 1: Clamp Meter Parts.
The Clamp Meter has the following parts (see Figure 1),
- Split core
- Secondary winding
- Rectifier unit
- Strigger switch (mechanism for opening core)
- Ammeter
The meter consists of split core (1) which can be opened to accommodate primary (i.e. cable, bus bar, conductor, feeder) by pressing a strigger switch (4). On the bottom of the core secondary winding (2) is accommodated, ac voltage induced in this winding is converted into d.c by a rectifier unit (3). D’arsonval movement ammeter (5) is connected to the rectifier to receive d.c. for operation.
The arrangement of conductor (feeder) is primary, coil on core is secondary, forms a step down transformer circuit. Though the meter is connected to secondary, its scale is calibrated to read primary current (i.e. current to be measured of H.T. feeder, cable).
Advantages of Clamp Meter
- Clamp on meter is generally used for HV line currents.
- Accuracy is about 3% of full scale with conductor is located at the central portion of the core.
- The instrument can be operated by one hand.
- It is useful for measuring AC current only and not DC.
