AC/DC Clamp Meters: Fluke
Clamp Meter - an Irreplaceable Tool for Measuring Electrical Currents
Clamp meter (also referred to as tong tester or clamp-on ammeter) is a very useful and convenient measuring tool widely used by electrical engineers all over the world. The main function of a clamp meter is measuring electric current properties of conductors without the need to interrupt an electrical circuit or physically touch the wires. They may also be supplemented with additional functionality, such as measurements of voltage, resistance, capacitance, frequency, temperature etc. This device makes conducting measurements very easy and convenient, especially in uncomfortable or hard to reach places. It is very often confused with a regular multimeter or misconceived as a multimeter with clamps instead of test lead. Though quite similar, their main functionality does differ, as the main function of a multimeter is voltage measurement, which is only sometimes supplemented with the ability to measure currents.
Depending on the method of measurements clamp meters are divided into AC current and DC current measurement devices. The first type uses an electromagnetic induction principle to conduct measurements while the second type uses a Hall Effect principle for theirs. The induction method is not that accurate and is only suitable for measuring high AC currents. Hall Effect method, on the other hand, is very precise and can measure DC and AC currents of both high and low magnitude.
The main part of an AC clamp meter is a current transformer, located in its jaws. It is a well-known fact that electric current produces a magnetic field around the wire that it flows through. Because of the alternating current’s tendency to frequently reverse its polarity, dynamic fluctuations (which are proportional to the current flow) appear in the magnetic field. These fluctuations are detected by the current transformer and converted to an AC current reading.
Obviously, this method cannot be used in DC clamp meters. DC current does not change its polarity, no fluctuations of the magnetic field appear around the wire and, therefore, a current transformer is not able to detect any current flow. A Hall Effect method had to be introduced in the meter in order to make it possible to measure DC currents. The main part of such meter is a Hall Effect sensor. It is located at the edge of one of the jaws, in the place where both jaws touch. The magnetic field around the wire causes a voltage (proportional to the current) to appear across the Hall Effect sensor. It is then amplified and measured.
Just as with any other measuring equipment, clamp meters wary in both price and feature range: from a cheaper ones with only basic features to expensive specialized ones that have a wide range of features. Some of the most popular features are:
- Data logging. Some models are supplied with a built in memory that allows recording several measurement results.
- Connecting to PC. More and more often these devices are provided with special software and an ability to be connected to a computer (usually via a USB cable). This allows all the measurement data to be transferred to a computer where it can be manipulated, analyzed and organized.
- Auto range. Some devices can set a measurement range automatically so that there is no need adjusting the switch to the right position to obtain accurate results.
- True RMS (Root Mean Square). True RMS provides more accurate AC current measurements by converting AC signal to an equivalent DC current signal.
The complete list includes a lot more additional features. Therefore, it is very important to consider what will be the primary use of the device when choosing one.