Clamp meter is often known as Tong Tester also. It is easy to use test equipment and is useful in the measurement of a live-conductor without interrupting / breaking the circuit. One of the biggest advantage of this equipment is that one may take the measurement of a high value current even without powering off/shutting down the circuitry under test.

There are two basic types of tong testers available in the market depending on the nature of current to be measured. One is for measuring DC (Direct Current) and the another-one is for measuring AC (Alternating Current). As earlier discussed, This test equipment is advantageous as compared to rest of current-measuring test equipments in terms of its ability to measure current without damaging / powering down the circuit. The only disadvantage of this test equipment (Clamp meter or Tong tester) is that the accuracy of the tog-tester is considerably low.

A view of clamp meter

Normally, Tong Tester functions on the fundamentals of Current-transformer. Whenever a current flows through a conducting material, it causes the generation of magnetic-flux. Now, let us assume that the conducting material from which the current is passing through is the primary arm of the transformer. Due to the current’s movement, a magnetic-flux is generated in it. When the arm of tong tester is placed for measurement, it acts as a secondary winding of the transformer. The arm of tong tester senses the magnetic flux of the primary winding (i.e. conductor) and hence a current in proportion to the primary-current is generated by electromagnetic-induction. This arm of the tong tester is connected to a measurement circuitry which in turn provides the current-reading finally.

Tong tester's block diagram

Operating Procedure

  • Switch ON Clamp meter (Tong tester).
  • Only a higher scale-value should be selected in order to avoid any harm to the circuit. Slowly decrease the scale reading selector if current is less.
  • Clip ON ammeter around each cable in turn and measure current.
  • Keep it in mind that current of only one cable each to measured at one time.