How to choose a current clamp: characteristics and tips for choosing

Recommendation points

• Why do you need current clamp
• Measurement methods
• AC current clamp
• DC current clamp
• Clamp meter measurement
• Measurement of current flowing through one conductor
• Simultaneous measurement of current flowing through multiple conductors
• Strengthening weak signals
• Varieties of current clamps, their advantages and disadvantages
• Clamp meter with dial indication
• Clamp meter with digital indication
• Clamp meter for connection to multimeters and oscilloscopes
• High Voltage Clamp Meter
• Additional features of the current clamp

The article discusses the device of a current clamp, their use for measuring alternating and direct currents without breaking an electrical circuit, provides measurement techniques, a comparison of the most common models, recommendations for choosing.

Why do you need current clamp

It is possible to measure the AC or DC current flowing through the conductors without breaking the electrical circuit, only with the help of a current clamp. This allows you to control the electrical current consumed by various installations and devices without stopping the operation of the equipment and performing additional installation work. Thanks to this feature, the current clamp is the second most popular device after a multimeter in the arsenal of a professional electrician..

The most common current clamp design:

1. Clamp-shaped magnetic core.
2. Magnetic circuit opening button.
3. Measurement method switch.
4. Electronic display.
5. Probe sockets.
6. Button for fixing measurement results in the device memory.

VOLTCRAFT VC 605

Measurement methods

For the manufacture of the current-sensitive part of this device, two types of sensitive elements are used, made on the basis of a Hall sensor or a special transformer. Depending on the type of analyzer, the current clamp can measure either AC and DC or AC only. Let’s consider the principle of their work in more detail.

AC current clamp

These current clamps are the most common due to their simple design and low cost. Their principle of operation is based on the use of the effect of transformer signal amplification..

1 – electrical circuit; 2 – conductor; 3 – transformer; 4 – ammeter; 5 – magnetic circuit

The measurement is very simple:

1. A conductor is started in the sliding magnetic circuit, on which it is necessary to measure the current.
2. This conductor for the coil wound on the magnetic core is the primary winding of the transformer.
3. Depending on the magnitude of the alternating current flowing through the conductor, the voltage at the output of the measuring element will change.

DC current clamp

These devices appeared after the discovery of the so-called Hall effect – a change in the strength of the magnetic field in a conductor through which an electric current flows, contributing to the formation of a potential at the measurement point corresponding to the magnitude of the magnetic flux applied to the semiconductor. Based on this effect, a special sensor has been developed that is sensitive to both alternating and constant magnetic fields..

1 – magnetic circuit; 2 – main current; 3 – conductor; 4 – Hall sensor; 5 – output current; 6 – compensation coil

An additional advantage of using a Hall sensor is its speed, which allows the use of devices built on its basis to detect short current surges.

Clamp meter measurement

There are several methods for measuring the current flowing through a conductor..

Measurement of current flowing through one conductor

This is the most common measurement method. The conductor is inserted into the magnetic clamps, which are located at right angles to the plane of the conductor. The required measurement range is set on the device. The measured current value will be displayed on the device screen.

Simultaneous measurement of current flowing through multiple conductors

If several conductors are brought into the magnetic circuit of the current clamp at once, then the device measures the difference value of the current flowing through them. For example, if for a 220 V network to simultaneously measure the current on the “phase” and “zero” of one circuit, the device will show the leakage current in the load.

Strengthening weak signals

To measure small currents, it is allowed to amplify the signal supplied to the sensor by winding the conductor around the magnetic circuit of the device. In this case, the real value of the current flowing through it is determined by dividing the current value obtained on the device indication by the number of turns made by the wire.

Varieties of current clamps, their advantages and disadvantages

Clamp meter with dial indication

KYORITSU KEW SNAP 2608A

This type of device is one of the first to use transformer systems for measuring alternating current with a variable number of turns on the secondary circuit..

Advantages:

• the device has a minimal cost, in the operating frequency range it measures the effective current value with high accuracy.

Disadvantages:

• can only work in a narrow frequency range.

The use of arrow indication makes it sensitive to shocks and reduces the measurement accuracy.

Clamp meter with digital indication

Fluke 376

Most modern devices are produced with a microcontroller signal processing system, this makes it possible to simplify the readout of the device readings, use automatic calibration of the measurement range, organize the recording of the measured current value into the device memory.

Advantages:

• easy to handle.

Disadvantages:

• low accuracy of current measurement, which differs in shape from a sinusoid.

Clamp meter for connection to multimeters and oscilloscopes

Fluke i410

This type of measuring instruments is used to expand the capabilities of existing instruments (multimeters, oscilloscopes, etc.). Their main feature is the absence of the measured signal indication on the housing of the device..

Advantages:

• high-precision measurement of parameters.

Disadvantages:

• an additional indicator is required for operation.

High Voltage Clamp Meter

Ts4502

To work with high-voltage circuits with voltages above 1000 V, special devices with improved electrical insulation are used, which guarantees the safety of the worker during measurements. Such devices allow you to control the current at various transformer substations and distribution nodes..

Advantages:

• the ability to work with high-voltage equipment.

Disadvantages:

• the ability to measure only alternating current in a narrow frequency range.

Additional features of the current clamp

Since the digital current clamp already includes an ADC used for processing analog signals, most manufacturers make this device universal, adding the ability to measure circuit voltage and resistance, temperature, etc..

Mastech M266

Many devices combine the capabilities of a full-fledged multimeter and a current clamp, while their cost is only slightly higher than analogs, but an order of magnitude more expensive than similar multimeters.

When choosing a current clamp, it is necessary to determine their capabilities (measurement of alternating or alternating and direct currents), shape (prefix or full-fledged device, special form, etc.), with the required measurement accuracy, operating frequency range, availability of the device necessary for operation additional functions. Only by comparing the desired functionality and financial capabilities, you can make the acquisition of the most practical and convenient device.