A clamp meter (clamp-on ammeter) is a type of ammeter which measures electrical current without the need to disconnect the wiring through which the current is flowing. Wire carrying current to be measured Spring providing restoring force An ammeter is a measuring instrument used to measure the flow of electric current in a circuit. ... In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ...

Clamp meters are also known as tong testers or Amprobes, (after one of the first vendors of such devices).

The most common forms of clamp meter are:

• A probe for use with a multimeter.
• A self-contained unit.
• A built-in part of a specialised multimeter used by electricians.

A multimeter with a built in clamp facility.
Pushing the large button at the bottom opens the lower jaw of the clamp, allowing the clamp to be placed around a conductor (wire).

In order to use a clamp meter, the probe or clamp is opened to allow insertion of the wiring, and then closed to allow the measurement. Only one conductor is normally passed through the probe, if more than one conductor were to be passed through then the measurement would be a vector sum of the currents flowing in the conductors and could be very misleading depending on the phase relationship of the currents. In particular, if the clamp were to be closed around a mains extension or similar cord, no current will be measured at all as the current flowing in one direction will cancel that flowing in the other direction. A digital multimeter A low cost digital multimeter An analog benchtop multimeter A multimeter or a multitester is an electronic measuring instrument that combines several functions in one unit. ... AC clamp meter This is an original photograph by Andrew Alder, taken on 11 November 2003. ... AC clamp meter This is an original photograph by Andrew Alder, taken on 11 November 2003. ... This article is about a portion of a periodic process. ...

In practice, nearly all clamp meters are used by electricians and the meters often include additional circuitry to allow the reading of voltage and, sometimes, resistance. The meters also often contain a mechanical pointer-locking device so that a reading can be taken in locations where the meter pointer can't be seen, the pointer then locked, and the meter brought out to a more-convenient place for reading. For the meter shown in the picture, the white push-button marked "lock" provides this function. International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... Buttons on a handheld calculator. ...

AC ammeters

Older clamp meters are AC devices only. The probe consists of a core of ferromagnetic material, which when closed forms the core of a transformer of which the wiring passing through the clamp is the primary winding. The instrument or probe contains a secondary winding of many turns. By measuring the current induced in this secondary winding, and taking account of the characteristics of the transformer and the frequency and waveform of the current being measured, the size of the current flowing through the conductor can be determined. Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... For other uses, see Transformer (disambiguation). ...

Less-expensive clamp meters use an average-detecting rectifier circuit that is then calibrated to read in RMS units; it is assumed in their design that the current is a sine wave of the local mains frequency, that is, either 50 or 60 Hz. If either of these assumptions are violated, incorrect readings may be obtained so when such 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, the readings produced by such meters can be quite inaccurate. In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... In trigonometry, an ideal sine wave is a waveform whose graph is identical to the generalized sine function y = Asin[ω(x − α)] + C, where A is the amplitude, ω is the angular frequency (2π/P where P is the wavelength), α is the phase shift, and C is the... Mains may mean or refer to, or be a subject of: Mains electricity Electricity transmission Public utility, about mains services, including electricity, natural gas, water, and sewage disposal Mains (Scotland), about the central steading of a townland BMX racing See also: Main Mane Category: ... A ballast is a device used to start a gas discharge lamp, and, once the lamp is started, to limit the flow of electric current. ... Fluorescent lamps in Shinbashi, Tokyo, Japan Assorted types of fluorescent lamps. ... 15 kW Xenon short-arc lamp used in IMAX projectors High-intensity discharge (HID) lamps include these types of electrical lamps: mercury vapor, metal halide (also HQI), high-pressure sodium (Son), low-pressure sodium (Sox) and less common, xenon short-arc lamps. ... This article is about the machine. ... This article is about the engineering discipline. ...

At the other extreme, probes sold for use with some computerised digital multimeters use true-RMS converters that will give accurate readings in almost any situation. These high-end meters may also replace the transformer secondary winding with a Hall effect sensor that allows accurate readings over a much-wider frequency range, often extending from DC to thousands of hertz and occasionally, for small clamp meters with ferrite cores, extending into the megahertz range. The magnetic piston (1) in this pneumatic cylinder will cause the Hall effect sensors (2 and 3) mounted on its outer wall to activate when it is fully retracted or extended. ... Ferrite may refer to: Ferrite (magnet)s (e. ...

A clamp meter with temperature sensing capability

DC ammeters

Newer units often read both AC and DC current. A Hall effect device is used to detect the DC magnetic field induced into the clamp. The signal from the Hall effect device is amplified and displayed using a built-in DVM. Typical handheld units can read currents as low as 200mA, and units which can read down to 1mA are available. Hall effect diagram, showing electron flow (rather than conventional current). ... A veterinary surgeon removes stitches from a cats face following minor surgery on an absess. ...

Related devices

Clamp probes are also sold for use with oscilloscopes. In this case, there is no rectifier (converter) circuit and the current waveform is presented directly to the 'scope's input. Such probes are available in both Hall-effect and inductive forms, for DC or AC applications. Illustration showing the interior of a cathode-ray tube for use in an oscilloscope. ...

An iron vane type clamp-on ammeter

The Columbia tong test ammeter, manufactured by Weschler Instruments, is a clamp-on ammeter with an iron vane movement used for measuring large AC currents up to 1000 amps. 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 4-1/2" (114mm) wide. Image File history File links Columbia_Ammeter_02. ... Image File history File links Columbia_Ammeter_02. ...