Home » , , » What is A Clamp Meter? How does A clamp meter work? How To Use a Clamp meter?

# What is A Clamp Meter?

An electrical meter with integral AC current clamp is known as a clamp meter, clamp-on ammeter or tong tester.
In order to use a clamp meter, only one conductor is normally passed through the probe; if more than one conductor is passed through then the measurement would be the vector sum of the currents flowing in the conductors and would depend on the phase relationship of the currents. In particular if the clamp is closed around a two-conductor cable carrying power to equipment the same current flows down one conductor and up the other, with a net current of zero. Clamp meters are often sold with a device that is plugged in between the power outlet and the device to be tested. The device is essentially a short extension cord with the two conductors separated, so that the clamp can be placed around only one conductor.
The reading produced by a conductor carrying a very low current can be increased by winding the conductor around the clamp several times; the meter reading divided by the number of turns is the current, with some loss of accuracy due to inductive effects.
Clamp meters are used by electricians, sometimes with the clamp incorporated into a general purposemultimeter.
It is simple to measure very high currents (hundreds of amperes) with the appropriate current transformer. Accurate measurement of low currents (a few milliamperes) with a current transformer clamp is more difficult.
Less-expensive clamp meters use a rectifier circuit which actually reads mean current, but is calibrated to display the RMS current corresponding to the measured mean, giving a correct RMS reading only if the current is a sine wave. For other waveforms readings will be incorrect; when these simpler meters are used with non-sinusoidal loads such as the ballasts used with fluorescent lamps or high-intensity discharge lamps or most modern computer and electronic equipment, readings can be quite inaccurate. Meters which respond to true RMS rather than mean current are described as “true RMS”.
Typical hand-held Hall effect units can read currents as low as 200 mA, and units that can read down to 1 mA are available.
The Columbia tong test ammeter, manufactured by Weschler Instruments, is an example of the iron vane type, used for measuring large AC currents up to 1000 amperes. The iron jaws of the meter direct the magnetic field surrounding the conductor to an iron vane that is attached to the needle of the meter. The iron vane moves in proportion to the strength to the magnetic field and thus produces a meter indication proportional to the current. This type of ammeter can measure both AC and DC currents and provides a true RMS current measurement of non-sinusoidal or distorted AC waveforms. Interchangeable meter movements can be installed in the clamping assembly to provide various full-scale current values up to 1000 amperes. The iron vane is in a small cylinder that is inserted in a space at the hinged end of the clamp-on jaws. Several jaw sizes are available for clamping around large conductors and bus bars up to 4+12 inches (110 mm) wide
you can see parts of a clamp meter in picture below:

# How To Use a Clamp meter?

## Measuring Current with a Digital Clamp Meter

1-Remove power from the circuit, if possible. Working on a hot circuit involves extra risk to the user and all equipment involved.
2-Isolate a wire carrying the current you wish to measure.
3-Open the clamp portion of the meter and then close it around the wire (and only that wire) you wish to measure current passing through.
4-Set the clamp meter to read the current type (AC or DC) and the expected range in milliamps or amps. If you don’t know the range, guess high, and dial down as needed.
5-Return power to the circuit and read the digital display, writing the value down to avoid repeating the process. If the reading fluctuates, give it a minute to settle down.
6-Remove power from the circuit. Then remove the clamp meter.
Using a digital clamp meter is an uncomplicated and safe way to measure current in a circuit. Unlike regular meters, the clamp type does not put the meter into the circuit, but measures the field induced by a current passing through the clamp. It is suitable for moderate (<480V) voltage and current applications.

# Tips & Warning

This type of meter is not for measuring current on a circuit board or for measuring small (<100 milliamps) current. This type of meter is not for precision current measurement. If a precise current reading is required, use an in-circuit meter.
-When working with electricity, always use proper safety techniques.