This section provides an overview for clamp meters as well as their applications and principles. Also, please take a look at the list of 11 clamp meter manufacturers and their company rankings.
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Clamp Meters are measuring instruments that can measure the current flowing in a cable by clamping the cable with a head (enclosing the cable with a core).
Since it does not need to be directly connected to the circuit under test, it has little effect on the circuit and can safely measure large currents. Normally, when measuring the current flowing in a wire or cable, the circuit is disconnected and an ammeter is inserted to measure the current.
However, this is a tedious process, so Clamp Meters are now used to measure current during electrical equipment inspections. In the past, there were analog types that displayed the measured value on a meter, but nowadays there are only a small number of such products, and digital types that display the numerical value on a display are the mainstream.
Clamp Meters are basically the same thing, but some testers have added functions to measure voltage and resistance in addition to current measurement. Voltage and resistance measurements are the same as those of ordinary testers, so this article will limit itself to current measurements.
The main use of Clamp Meters is to measure current during various electrical construction and inspection work in homes and businesses. The purpose is to measure the current flowing through a cable without cutting the cable.
Since there is no need to disconnect the cable each time a measurement is made, a major advantage is that the current can be measured while lighting and equipment are operating as usual. In addition, highly sensitive models that can measure minute currents can also be used to measure leakage currents flowing from equipment to ground.
Clamp Meters are based on the function of a transformer. The head that clamps the cable corresponds to the core of a transformer and is made of a highly permeable magnetic material (iron-based material such as Permalloy). A transformer is capable of converting an alternating current added to the primary side into a voltage or current on the secondary side according to the ratio of the number of turns on the primary and secondary sides.
If a cable with current flowing through it is placed inside the core, it will act as the primary winding of the transformer. A coil corresponding to the secondary winding is also installed in the head, through which the current flows, and the current value is measured to calculate the current value flowing in the cable.
However, the method using a transformer for current detection cannot measure DC current because current does not flow in the secondary winding. For this reason, the AC/DC dual-use type, which can also measure DC current, uses a head with a Hall element embedded inside the core. The Hall element outputs a voltage corresponding to the magnetic flux density due to the Hall effect for both DC and AC, and this voltage is measured to calculate the current value flowing through the cable.
Operation of the Clamp Meters is extremely simple: simply clamp the cable between the heads. Placing the cable in the center of the head minimizes the measurement error, but even a slight deviation will not have a significant effect.
When measuring DC current, attention should be paid to the direction of the current flowing through the cable. The head of most Clamp Meters is marked with a "+" and "-" symbol. This is a guide to indicate the direction of the current. When the DC current flows from "+" to "-", it is a positive current value, and when it flows from "-" to "+", it is a negative current value.
When measuring the current flowing in a device, either the outward or return cables are passed through the head. When the outward and return cables are passed through the head, the magnetic flux density should cancel each other out and the current value should be 0A. However, if there is leakage current inside the equipment, part of the current will flow to ground, resulting in a slightly lower current on the return path than on the outward path.
The magnetic flux density corresponding to the difference is generated and displayed on Clamp Meters, which is equal to the magnitude of the leakage current. Using this principle, it is possible to measure the leakage current of a device. Since the leakage current is several mA to several tens of mA, the sensitivity of the Clamp Meters to be used should be about 1 mA.
When measuring currents in parallel cords with Clamp Meters, accessories such as line separators can be used to separate the parallel cables, facilitating measurement. In addition, the use of a wireless adapter that transfers measurement data directly to a PC via wireless communication is very useful in preventing data transcription errors in field work.
*Including some distributors, etc.
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Founded in 1940, Kyoritsu has an 80 year history as a customer-focused organization specializing in multimeters. Kyoritsu provides analog multimeters as well as digital multimeters with and without clamps offering many varieties of measurement.
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