A current clamp is a device used in electrical and electronic engineering, to measure electrical current in a conductive material. It consists partly of a pair of jaws that close around an electrical conductor, to measure how electricity flows through the material. Some types of current clamps are used to induce a current into the conductive material, as well as measuring that current.
One variety of current clamp is the iron vane. In this type of current clamp, the electrical current being measured causes a change in the internal magnetic core of the device. This changing magnetic field moves an iron vane, which is fixed in turn to a pointer on an analog dial. An iron vane clamp meter can be used to measure both direct current (DC) and alternating current (AC).
The most common form of current clamp is often found in current transformers, and serves a slightly different purpose than the iron vane type. In these, a split ring made of iron compounds has a wire coil wound around it. This winding is the secondary part of a current transformer, with the conducting material forming the primary part. The current clamp found in transformers is used to measure current in the power grid, and to monitor its operation. Transformers only work with AC electricity, so this type of current clamp is therefore only useful when measuring AC.
Another type of current clamp which measures AC as well as DC is the Hall effect type. The name refers to the Hall effect, which is the influence that a magnetic field has on the flow of electrons in a conductor. These current clamps are highly sensitive and are often used with computerized voltmeters. They can be small enough to be hand-held and run on a nine-volt battery. Hall effect clamps can also work with a wide range of AC frequencies, sometimes up to 400 Hz.
In the field of biology, a certain highly specialized type of current clamp is used to measure voltages produced by the action of a single cell. Cellular current clamps can record electrical activity both outside and within a cell. The devices which measure and record biological voltages do so through a microelectrode, which is small enough to be able to measure cellular electricity. The voltages they record are usually minute- on the order of 0.0001 volts.