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  • 클램프메타에 대한 정보


  • ◈ 클램프 메타(Clamp meter)에 대하여...
       ▶ How do clamp meters Operate ?
       ▶ True RMS value...
       ▶ Measurement Principle of AC/DC Clamp    Meter
       ▶ How to Measure DC Current
    ◈ 누설 전류(leakage current) 측정 방법에 대하여...

    ◈ 클램프 메타(Clamp meter)에 대하여...

    Fig.1 Measurement using multimeterFig.2 Measurement using Clamp meter Clamp meters are a very convenient testing instrument that permits current measurements on a live conductor without circuit interruption. When making current measurements with the ordinary multimeter, we need to cut wiring and connect the instrument to the circuit under test as shown in Fig.1
    Using the clamp meter, however, we can measure current by simply clamping on a conductor as illustrated in Fig.2. One of the advantages of this method is that we can even measure a large current withort shutting off the circuit being tested.
    ▶ How do clamp meters Operate ?
    Operation Principle of clampmeter In general AC clamp meters operate on the principle of current transformer(CT) used to pick up magnetic flux generated as a result of current flowing through a conductor.
    Assuming a current flowing through a conductor to be the primary current, you can obtain a current proportional to the primary current by electromagnetic induction from the secondary side(winding) of the transformer which is connected to a measuring circuit of the instrument.
    This permits you to take an AC current reading on the digital (in the case of digital clamp meters) as illustrated by the block diagram.
    ▶ True RMS value...
    CF : Crest Factor=Peak value/RMS value
    DC=1
    Sine wave=1.414
    True RMS Value Most alternating currents and voltage are expressed in effective values, which are also referred to as RMS(Root-Mean-square) values.
    The effective value is the square root of the average of the square of alternating current or voltage values.
    Many clamp meters with rectifier type circuits have scales that are calibrated in RMS values for AC measurements.
    But, they actually measure the average value of input voltage or current, assuming the voltage or current to be a sine wave.
    The conversion factor for a sine wave, which is obtained by dividing the effective value by the average value, is 1.1
    These instruments are in error if the input voltage or current has some other shape than a sine wave.
    ▶ Measurement Principle of AC/DC Clamp Meter
    Measurement Principle of AC/DC Clamp meter In general hall elements are used as a sensor to detect DC current because it is not possible to employ an electromagnetic induction method as used for dedicated AC clamp meters As shown in a figure at left, a hall element is placed across a gap created by cutting off part of the transformer jaws.
    When there occurs a flow of magnetic flux proportional to both AC and DC primary currents in the transfomer jaws this hall element detects the magnetic flux and takes it out as an output voltage.

    Hall element : This a semiconductor to generate a voltage proportional to the product of bias current and magnetic field on the output terminal when bias current is applied to the input terminal.
    ▶ How to Measure DC Current
    Measure DC Current Clamp on to a conductor just the same way as with AC current measurement using an AC current clamp meter

    In the case of DC clamp meters the reading is positive(+) when the current is flowing from the upside to the underside of the clamp meter

    ◈ 누설 전류(leakage current) 측정 방법에 대하여...

    Broadly speaking, there are two methods of leakage current measurement.
    One is designed to measure leakage current by directly clamping on an earthing conductor
    and the other is intended to measure leakage current by clamping on two-way wires togather.

    Method of leakage current measurement Please refer to Fig.1 for respective measurement methods.

    The principal of measurement involving the clamping of two-way wires together
    is meant to find out the difference of current flowing
    between the incoming wire and outgoing wire and display the result.
    If there is no leakage on the load side, the instrument display reads zero.
    If the leakage occurs on the load side, the leakage current will flow back into the power supply
    through earth, resulting in the difference of current flowing between the two-way wires
    which will then be displayed on the instrument as a value of leakage current.

    Specifications & Models are subject to change without notice.
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