|What Are Clamp Meters?
|Clamp meters are a very convenient testing instrument that permits current measurements on a live conductor without circuit interruption. When making current measurements with the ordinary multimeter, we need to cut wiring and connect the instrument to the circuit under test as shown in Fig.1.
Using the clamp meter, however, we can measure current by simply clamping on a conductor as illustrated in Fig.2. One of the advantages of this method is that we can even measure a large current without shutting off the circuit being tested.
|How to Measure DC Current
|Clamp on to a conductor just the same way as with AC current measurement using an AC current clamp meter. In the case of DC clamp meters the reading is positive (+) when the current is flowing from the upside to the underside of the clamp meter.
|Clamp Meter Principle
|Measurement Principle of AC/DC Clamp Meter
In general hall elements are used as a sensor to detect DC current because it is not possible to employ an electromagnetic induction method as used for dedicated AC clamp meters. As shown in a figure at left, a hall element is placed across a gap created by cutting off part of the transformer jaws. When there occurs a flow of magnetic flux proportional to both AC and DC primary currents in the transformer jaws this hall element detects the magnetic flux and takes it out as an output voltage.
Hall element:This is a semiconductor to generate a voltage proportional to the product of bias current and magnetic field on the output terminal when bias current is applied to the input terminal.
How Do Clamp Meters Operate?
In general AC clamp meters operate on the principle of current transformer(CT) used to pick up magnetic flux generated as a result of current flowing through a conductor. Assuming a current flowing through a conductor to be the primary current, you can obtain a current proportional to the primary current by electromagnetic induction from the secondary side(winding) of the transformer which is connected to a measuring circuit of the instrument. This permits you to take an AC current reading on the digital display(in the case of digital clamp meters) as illustrated by the block diagram.
|Select and set the standard resisitance value in each measuring range, and compare it with readings.
Notice the result of comparison by the or sign on the display, and by buzzer sound at same time.
Buzzer can be set either for or at your choice.