Clamp Meter

Here you may find all the important information on the topic Clamp Meter. A clamp meter is an ideal instrument for indirect, contactless and simultaneously potential-free current measurement in the AC (Alternating Current) and DC (Direct Current) current range. The conductor to be measured must be brought into the interior of the divisible iron core, which is located in the measuring jaws of the clamp meter. A disconnection of the circuit, as in direct measurement, is not necessary for the current measurement due to the clamp meter. The clamp meter is indispensable when it goes about maintenance and inspection work, in various industrial applications, in research and development, in SMEs or private households. The digital clamp meter has the possibility of measuring many other parameters, such as capacity measurement, power measurement (either as a single clamp meter or as a digital hand-held meter with an external clamp meter in a single or three-phase range), resistance measurement, continuity test and voltage measurement. Thus, the clamp meter is not only suitable for measuring currents, but it is rather a multifunctional test device for a large number of electrical parameters.
The range of the clamp meters is diverse: clamp meters, leakage clamp meters, power clamp meters, clamp meters, flexible clamps, fork clamps and clamp ammeters. Like most of the test devices we offer, the clamp meter is available without or with an ISO calibration certificate or with a DAkkS calibration certificate.

It is known from the basics of electrical engineering that current must always be measured in series to a consumer. The internal resistance of the ammeter then always inevitably leads to a change in the overall circuit. Therefore, the internal resistance must be as small as possible. However, it is often not possible to open the current circuit for measuring the current with an ammeter or the current in the AC network is very high, so that a contact current measurement is not possible. This is where a clamp meter comes handy.

General operating principle of the clamp meter
Around each electrical conductor through which a current flows, a magnetic field spreads linearly with the flowing current. This is a DC magnetic field for direct current and an alternating magnetic field for alternating current. Clamp meters make use of this effect and, depending on the type of the current, measure the current via a Hall sensor (direct current) or via the transformer principle (alternating current).

Which clamp meter should be used?
The choice of the clamp meter depends on various factors. The first factor is the type of the current. The most common is the clamp meter for alternating current. For applications in which also direct current is to be measured with the help of the clamp meter, in order, for example to measure the current from a PLC system, the clamp meter is required that can measure direct current. Often, the clamp meters which measure the direct current also measure the alternating current.

Another question about choosing the right clamp meter is the strength of the electric current. In general applies the following: the higher the current to be measured is, the larger the design of the clamp meter is. The Rogowski coil is a special type of the clamp meter. This type of clamp meter is often used for very high alternating currents, since extremely large sizes can be achieved here. The great advantage of the clamp meter based on the Rogowski coil is that the measuring coil is very flexible compared to the measuring jaws of the clamp meter based on the ferrite core. Flexible clamp meters are often used, especially when it goes about measurement in the control cabinet, and also in many other places that are difficult to access.

Clamp meters are also often used to measure the electrical power. This special form of clamp meter is widely used in electrical measurement technology. The following must be observed here: the power measurement with the help of the current probe in a 3-phase network, which is also referred to as three-phase current, is always possible only when there is a symmetrical load. However, symmetrical load is quite rare and in practice only occurs in case of a 3-phase motor or a 3-phase heater. In the case of asymmetrically loaded phases in a three-phase current network, a separate clamp meter must be used for each phase. PCE Instruments offers corresponding clamp meters with the power measuring functions. Since in the three-phase network the 3 currents of the different phases are measured with the respective clamp meter and also the voltage of the 3 phases including the neutral conductor, the user of the 3-phase clamp meter with power measuring function receives a whole range of the measured and calculated results. These are in detail: the voltages between the phases, the voltages between the phase and the neutral conductor, the phase current measured with the clamp meter, the active, apparent and reactive power per phase and total, the power factors, the phase shifts per phase and the active, blind and apparent energy.

A special measuring function in the clamp meter is the so-called inrush function. This function is used whenever the starting current of the machines or motors has to be measured. The clamp meter is in a kind of standby mode after activation. As soon as the current is registered through the clamp, it is detected with a very high sampling rate and the peak value is shown on the display, even if the current is again at a lower level after switching on.

A TRMS clamp meter is able to measure the TRMS current value. TRMS stands for True Root Mean Square. What is meant by this is that the TRMS clamp meter records the current at a high sampling rate and calculates it accordingly. The clamp meter without the TRMS function measures the peak value and assumes a sine wave and calculates the current value with the corresponding form factor. However, if the current is not sinusoidal because of the consumer or the original voltage form, the clamp meter displays an incorrect measured value. Other special functions such as voltage measurement or resistance measurement and temperature measurements complete the scope of services of the clamp meter.

The clamp meter is used for the indirect measurement of the electrical current in current-carrying conductors. In contrast to the direct current measurement, which requires the circuit to be checked to be open, the clamp meter measures without contact? Here, the devices use the basic physical principle of the magnetic induction, in which live cables induce a measurable electric field. Contactless measurement has several advantages. On the one hand, the measurements can be carried out also on the insulated conductors without having to interrupt the ongoing operation of the electrical devices and machines. On the other hand, this method dispenses with the potential coupling of the measurement variable and measurement signal, which avoids measurement inaccuracies.

By determining the strength of the electrical field that surrounds an electrical AC conductor, the clamp meter can determine the current strengths of the alternating current very precisely. The clamp meter for direct current determines the current with the help of the Hall sensor. This measures the magnetic field around the conductor through which the DC current flows. To do this, the live conductor is led through a laminated, insulated and divisible core on the front of the clamp meter. Modern clamp meters transmit the resulting magnetic field via the clamps to the electronic circuits and amplifiers inside the clamp meter and convert the E field or the magnetic field strength, depending on the setting and design, into direct current or alternating current. The measured value is usually shown on the clamp meter on an LC display. Depending on the design and size of the clamp meter, this display can visualize the graphical courses.

Here you may find an information video about our clamp meter PCE-DC 3

In this video, Mr. Ludger Göckeler presents the PCE-DC 3 clamp meter very clearly.

The corresponding measured values can then be read on a digital display. The measuring range of this indirect and practical measuring method is limited by two parameters. On the one hand, very small currents can hardly be measured with clamp meters because the induced magnetic fields can no longer be detected. On the other hand, the conductor cross-sections necessary for large currents and the correspondingly dimensioned clamp cores limit the manageability of these measuring devices. Even if the current clamp is not the ideal measuring device for particularly small currents and extremely large conductor cross-sections and for the measurements in inaccessible places, the performance spectrum of this practical and fast measuring instrument is sufficient for a multitude of applications. One example of this is an automotive technology. Here, the defective vehicle electronics can be examined with the help of the clamp meter. The latter is also a useful auxiliary tool when searching for leakage currents inside a vehicle. These devices are used in many areas: from a simple application in a private life for hobbies, to the workshop use, to large-scale analysis and evaluation of electrical quantities by technicians and engineers.

The current clamp shows "zero" even though a current is flowing.

This phenomenon occurs when the conductors of L1 and N are located simultaneously within the measuring jaws in the 1-phase network. Then the magnetic fields of the two conductors cancel each other out and therefore no current can be measured by the clamp meter.

Very small streams

With very small currents, it is sometimes very difficult for a clamp meter to display a measured value. In this case the conductor can be wound several times around the measuring jaw of the clamp meter. The displayed result must then be divided by the number of turns.