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In electrical and electronic engineering, a current clamp, also known as a current probe, is a jaw-bearing electrical device that allows clamping around electrical conductors.

This allows the current to be measured without the need for physical contact with the current in the conductor or to disconnect it for insertion through the probe.

Current clamps are commonly used to read the levels of alternating current (AC) and the phase and waveform can also be measured with the help of additional instruments.

Some clamp meters can measure currents of 1000 A and more. Hall effect and VEN type clamps can measure direct current (DC).

An introduction to clamp meters

What is a clamp meter and what can it do? What measurements can be made with a clamp meter? How do you get the most out of a clamp meter? Which clamp meter is best suited to the environment the meter will be used in?

Note this question The answer to this question can be found. With the technological advancement of electrical equipment and circuits come more challenges for electricians and technologists. These advances not only require more expertise in today’s testing tools but also more expertise on the part of those who use them.

An electrician who has built a good foundation on the basics of using test equipment will be better prepared for today’s test and problem solving challenges. The clamp meter is an important and common tool that is found in toolboxes like electronics and technicians.

A clamp meter is an electrical tester that combines a voltmeter with a clamp type current meter. Like the multimeter, the clamp meter has gone into the analog period and in today’s digital world. Originally designed as a single-purpose test tool for electronics, today’s models feature more measurement functions, more accuracy, and some very special measurement features in some instruments.

Today’s clamp meters have many of the basic functions of a digital multimeter (DMM), but with the added features of a current transformer built into the product. The capacity of the clamp meter to measure large AC currents is based on simple transformer action.

When you play the “jaws” of the device around the conductor carrying the AC current, the current that is connected to the shuttle of the meter input is connected through the joints like the iron core of a power transformer and with a secondary winding. Due to the ratio of the number of secondary windings, the much smaller current is supplied to the input of the meter. The number of primary windings wrapped around the core.

Typically, the primary is represented by a conductor around which the jaws are clamped. If the secondary has 1000 windings, then the current flowing in the secondary current primary or 1/1000 current case or the conductor is being measured. Thus, the conductor being measured can produce 0.001 MPS or one milliamp current at the input of the 1 MP current meter. Many large currents can be easily measured by increasing the number of secondary turns with this technique.

What is a clamp meter?

A clamp meter is an electrical test device that combines a basic digital multimeter with a current sensor. Clamp current measurement. Measures probe voltage.

Integrating an embossed jaw into an electric meter allows technologists to clamp the jaws around a wire, cable, or other conductors anywhere in the electrical system, then measure the current in that circuit without disconnecting/disconnecting.

Beneath their plastic molds, the hard jaws contain ferrite iron and are engineered to detect, condense, and measure the magnetic field produced by the current as it flows through the conductor.

  1. Current sensitive jaw
  2. Sensitive barrier (to protect fingers from pushing).
  3. Hold button: Display reading freezing. Reading is revealed when the button is pressed a second time.
  4. Dial (aka Rotary Switch).
  5. Display.
  6. Backlight button
  7. Minimum Maximum Button: On the first push, the display shows the maximum input. In subsequent pushes, minimum and average inputs are displayed. Works in current, voltage and frequency modes.
  8. Stop the current button.
  9. Zero buttons (yellow): DC removes DC offset from current measurement. The yellow also acts as a shift button to select the yellow functions scattered around the dial.
  10. Jaw release lever
  11.  Alignment marks: To specify the accuracy, a conductor must be combined with these marks.
  12. General input jack.
  13. Volts/ohm input jack.
  14. Input for the flexible current investigation.

Originally designed as a single-purpose test tool, modern clamp meters provide more measuring functions, greater accuracy, and specialized measurement features.

Today’s clamp meters include the most basic functions of a digital multimeter (DMM), such as the ability to measure voltage, continuity, and resistance.

Clamp meters have become a popular tool for two main reasons:

.Safety. The clamp meter allows electronics to cut into a wire and bypass the old-school method of entering a meter test to take a lined in-line current measurement. A clamp meter jaw does not need to touch the conductor during a measurement.

Convenience. During a measurement, the current does not need to close the current-carrying circuit is a great incentive for efficiency. Clamp meters are preferred for measuring high current currents. DMMs cannot measure current at 10 for more than 30 seconds without the risk of meter damage. Clamp meters provide a current range of minimum 0 A to 100 A. Many models have a range of up to 600 A.

Others go up to 999 A or 1400 A and some plug-in clamp accessories like iFlex can measure up to 2500 A. Clamp meters are used in industrial equipment, industrial control, residential/commercial/industrial electrical systems and commercial/industrial HVAC. These are primarily used for:

Service: Repair existing systems as needed.
Installation: To troubleshoot installation problems, inspect the final circuit and supervise the trained electronics when installing electrical equipment.
Maintenance: Defective and preventive maintenance as well as system troubleshooting. There are three types of clamp meters:

Current transformer clamp meters: Measure only alternating current (AC).
Hall Effect clamp meters: Measure both alternating current and direct current (AC and DC).
Flexible clamp meters: Appointing a Rogogsky coil; AC measurement only; Good for measuring in tight spaces. Find the right clamp meter.

Types of clamp meters

Clamp meters, also known as clamp-on ammeters, sometimes even as tong testers, fall into three categories:

  1. Current transformer (ac) clamp meters.
  2. Hall Effect (ac and dc) clamp meters.
  3. Flexible (ac) clamp meters.

Although different, they share the same basic method when measuring: A conductor is passed through a probe (either a stiff latch built into a clamp meter, or a flexible coil of clamp accessories), and the vector sum of the currents flowing through the conductor is calculated by the meter—other special equipment related to the clamp meter section. Fluke’s product line solves a variety of specific problems with clamp-based tools. Some examples:

  • Basic electrical testing (example: Fluke T5-1000)
  • HVAC (Fluke 902 True-RMS HVAC Clamp Meter)
  • Accessory current clamps; plug-in clamps typically used with digital multimeters (Fluke i410 ac/dc Current Clamp)
  • Current leakage (Fluke 360 ac Leakage Current Clamp Meter)
  • Earth ground testing (Fluke 1630 Earth Ground Clamp Meter)
  • Process; for measuring 4-20 mA signals and others (Fluke 773 Milliamp Process Clamp Meter)
  • Power quality (Fluke 345 Power Quality Clamp Meter)
  • High current (Fluke 355 True-RMS 2000 A Clamp Meter)

Clamp Meters Working Principle

Clamp Meters using Current Transformer for AC Measurement

Current transformer clamp meters are equipped with rigid jaws made of ferrite iron. Copper wire coils individually cover the jaws. Together, they form a magnetic core during measurement.

Their basic operation is like a transformer. It works with an initial bend, or rotation, in which in almost all cases, the conductor is measured. The coils around the jaws act as secondary air to the current transformer. The current flowing through the conductor creates a magnetic field that revolves around it.

This field is centered by the iron core of the clamp, which induces the flow of the secondary winding in meters. The measurement of the amount of magnetic field through a conductor (or any surface) is called magnetic flux, denoted by the Greek letters fi, Φm.

The signal is proportional to the ratio of turns. Due to the ratio of the number of secondary windings (wrapped around the jaws of the clamps) versus the number, a smaller current is supplied to the input of the meter. The number of primary windings wrapped around the core.

If, for example, the secondary has 1000 windings, then the current flowing in the secondary current is 1/1000. Measuring thus the conductor can generate 0.001 MP or one milliamp current at the input of 1 MP current meter. Many large currents can be easily measured by increasing the number of secondary turns with this technique.

Internally, the current flow in the conductor can be measured as current – some old clamp accessories can be plugged into the current jacks of a digital multimeter – or converted to volts. Most clamp meters now have MV output. Current transformer clamp meters only respond to AC waveforms.

Clamp Meters using Hall Effect for AC & DC Measurements

Hall effect clamp meters can measure both AC and DC kilohertz (1000 Hz) range. Like the current transformer type, the Hall effect clamp connector meters use a hard iron jaw to condense the magnetic field in which the conductor is measured enc.

Unlike current transformer clamp meters, the jaws are not covered by copper wire. Instead, the magnetic field produced by the conductor is focused across one or more gaps in the core after pressing the jaws around the conductor.

Notice the point where the jaw tips of the clamp connection meter of the hall effect meet. There is a gap where the jaw tips of the clamp connection meter of the Hall effect meet and create an air pocket that the magnetic field (aka magnetic flux) must jump.

This gap limits the magnetic flux so that the core cannot fill.
In contrast, the current only flushes when the jaws of the current transformer clamp are closed. When opening, the tips of the jaws show empty metal core faces. In this gap, a semiconductor covered by a thin plastic mold is known as a Hall effect sensor – a transducer that changes its output voltage when responding to magnetic fields, in which case the magnetic field of the conductor or wire is being measured.

Its purpose is to measure magnetic flux directly. The output voltage from the sensor is wide and shaped to represent the current flowing through the conductor inside the clamp or debris.

When the conductor is flowing through the measurement, an iron core formed by the jaws of an impact clamp meter can easily pass through the magnetic field more easily than air. Magnetic field (flow) When that little air enters the gap at the tips of the jaw, the field has to override that gap.

Because the gap is small, the field is centered across the gap and is the Hall effect sensor – which sits in the gap and creates a voltage proportional to the magnetic flux in the gap that translates the clamp into the current text.

In the Hall effect device, the DC magnetic fields are centered through the core, like a permanent magnet with iron. Due to the DC magnetic field of the earth and the possibility of other magnetic fields near the measurement site, the text needs to be “zeroed” before a measurement can be made to remove the offsets of these clamps.

The American physicist Edwin Hall (1855-1938) was submitted in 1879 to discover the Hall effect.

Choosing your clamp meter

Buying a clamp meter requires not only looking at the specifications but also looking at the features, functions and overall quality represented by the design of the meter and the care taken in its production. Reliability, especially in difficult situations, is more important than it is today.

Fluke’s design engineers made these experimental tools not only electrically powerful but also mechanically. As fluke clamp meters are ready to be dispensed in equipment cases, they have undergone a rigorous testing and evaluation program.

User safety should be a primary consideration when choosing a clamp meter or any other electrical test equipment. Fluke not only designs its clamp meters to the latest electrical standards, but each is tested individually and then listed by certified tests such as UL, CSA, VDE, etc. Only with these certifications can you ensure that the electrical tester meets these new safety standards.

Some basics of clamp meter

Resolution, digits and counts

Resolution refers to how precisely a meter can measure.

By knowing the meter’s resolution, you can determine if it is possible to see any small changes in the measured signal. For example, if the clamp meter has a 0.1 MP resolution in the 600 MP range, it is possible to see a 0.1 MP change when reading 100 MP.

If you have to measure up to an inch, you can’t buy one marked in ¼ -inch segments. Similarly, you must choose a meter to display the resolution you need to see in your measurements.


How accurate are clamp meters?

Accuracy is the most permissible error that can occur under certain operating conditions. In other words, it is a measure of how close the actual value of the signal measurement is to the measurement displayed on the meter. The accuracy of a clamp meter is usually expressed as a reading percentage.

1% reading accuracy means that for a displayed reading of 100 MPS, the actual current value can be anywhere between 99.0 and 101.0 MPS. Specifications may also include different numbers added to specify basic accuracy.

This indicates how different the number of digits in the absolute right of the display can be. Thus the previous example of validity can be described as ± (2% + 2). Thus, for the displayed reading of 100.0 MPas, the actual current can then be assumed to be between 97.8 and 102.2 MPas.

Crest factor

With the rise of the electronic power supply, today’s electrical distribution system’s currents are no longer pure sine waves of 60 or 50 cycles. These currents have become fairly distorted due to the harmonious elements that supply this power supply.

However, the thermal components of electrical system components such as fuses, bus bars, conductors and circuit breakers are rated in RMS current because their main limitation is related to heat dissipation. If we want to test the electrical circuit for overloading, we need to measure the RMS current and compare the measured value with the value specified for the component in question.

Therefore, today’s test equipment must accurately measure the true-RMS value of a signal without determining how distorted the signal may be. The crest factor is a general ratio of the RMS value of the top quality of a signal. The crest factor for an authentic AC sine wave will be 1: 1.414.

However, the ratio or crest factor of a signal that has a very sharp pulse may be higher. You can see the crest factor of 10: 1 or more depending on the pulse’s width and frequency. In existing power distribution systems, crest factors greater than 3: 1 are rarely seen.

So as you can see, the crest factor is an indication of the distortion of a signal. A crest factor specification can only be found in the meter specification that can measure true-RMS. This indicates how much distortion a signal can have and can still be measured in the meter’s precision specification.

Most True-RMS Reading Clamp meters have a crest factor specification of 2: 1 or 3: 1. It will handle most electrical applications.

Measuring AC current

One of the most basic measurements of a clamp meter is the AC current. Current measurements are usually taken in different branch circuits of the electrical distribution system.

Determining how much current flows in different branch circuits is a fairly common task for electronics.

How to make ac current measurements?

  1. Select Amps ac
  2. Open the jaws of the clamp meter and close the jaws around the single conductor
  3. View the reading in the display

By taking measurements of a branch circuit running current, you can easily tell how much is being drawn from each load distribution system along the branch circuit. When a circuit breaker or transformer is overheated, it is best to measure the current branch circuit to determine the load current.

However, make sure you are using a True-RMS response meter to get accurate measurements of the heating signal of these components. If the current and voltage are non-sinusoidal due to a non-linear load, the average reactive meter will not give a true reading.

Measuring voltage

Another common job for a clamp meter is to measure voltage. Today’s clamp meters are capable of measuring both AC and DC voltages. AC voltage is usually generated by a generator and then distributed through an electrical distribution system.

Electronic problems are the ability to take measurements throughout the system to isolate and solve electrical problems. And a simple voltage measurement will test the battery voltage. In this case, you will measure the direct current or DC voltage.

Checking the proper supply voltage is usually the first thing that is measured when solving a circuit problem. If no voltage is present or too high or too low, the voltage problem should be corrected before further investigation. The power of a clamp meter for measuring AC voltage may be affected by the signal’s frequency.

Most clamp meters can accurately measure AC voltages with a 50 Hz frequency to 500 Hz, but the AC measurement bandwidth of a digital multimeter can be 100 kHz or more. This is why reading the same voltage by a clamp meter and a digital multimeter can have very different results.

The digital multimeter allows much more of a higher frequency voltage through the measuring circuit. Simultaneously, the clamp meter filters some of the voltage at the signal above the meter’s bandwidth. When solving variable speed drives (VSD) problems, a meter’s input bandwidth can become very important for getting meaningful readings.

Due to the high harmonic content of the signal emitted from the VSD in a motor, a DMM will measure most of the voltage content depending on its input bandwidth. Measuring the voltage output of a VSD is not a common measure; it Will be higher if you read.

A motor connected to a VSD only responds to the signal’s average value, and to measure that power, the meter’s input bandwidth must be narrower than its DMM portion. The Fluke 337 clamp meter is specifically designed for VSD testing and troubleshooting.

How to make voltage measurements

  1. Select Volts AC (V~) or Volts DC (V ), as desired.
  2. Plug the black test probe into the COM input jack. Plug the red test probe into the V input jack.
  3. Touch the search tips across a load or power source (parallel to the circuit).
  4. View the reading, being sure to note the unit of measurement.
  5. (Optional) Press the hold button to freeze the reading on display. Now you can remove the meter directly from the circuit and then you can read the display when it is safely cleaned from the danger of electricity.

By measuring a voltage at the circuit breaker and then at the input of that breaker’s load, you can determine the voltage drop that occurs through the wiring connector. A significant drop in voltage across the load can effectively affect the efficiency of the load.


Resistance is measured at Ohms (O). Resistance values can vary from a few milliohms (MO) to a few billion ohms of insulators’ contact resistance.

Most clamp meters measure down 0.1? “OL” appears on the meter’s display when the measured resistance exceeds the meter’s upper limit or the circuit is open. Resistance must be measured by turning off the circuit power – otherwise, the meter or circuit may be damaged.

Some clamp meters protect in ohms mode in case of accidental contact with voltage. The level of protection can vary greatly between different clamp meter models. A very common measure of electrical resistance is the resistance of a contactor coil.

Making a resistance measurement

  1. Turn off power to the circuit
  2. Select resistance
  3. Plug the black test probe into the COM input jack. Plug the red test probe into the V input jack
  4. Attach the search tips across components or parts of the circuit you want to determine the resistance
  5. View the reading in the meter’s display


Continuity is a fast go / don’t stop test that distinguishes between an open and a closed circuit. A clamp meter with a continuity beeper allows you to finish many continuity tests easily and quickly.

The meter goes off when it detects a closed circuit, so you don’t have to look at the meter during the test. The level of resistance required to trigger a beeper varies from meter to meter. The general resistance setting to turn on the beeper is to read less than 20 to 40 ohms.

Special functions

A fairly common measurement operation is the reading of the frequency of an AC current waveform. Wrap the clamp meter jaws around the conductor carrying the AC current, switch the frequency function, and display the meter will indicate the frequency of the signal flowing through the conductor. This is a very useful measure when identifying harmonious problems in electrical distribution systems.

Another feature found in some clamp meter models is the MIN Max storage. When this feature is enabled, each reading of the clamp meter is compared with the previously stored reading. If the new text is higher than the reading in higher reading memory, it replaces it as the maximum reading.

The same comparison is made against low reading memory and replaces it when it is less than the stored reading. All readings are processed this way as long as the MIN MAX feature is active. So, over time, you can call to display each value of this memory and set the maximum and minimum text in a certain period of time.

Electrologists who work with motors in their work can tell a lot about the ability to capture the amount of current drawn by the motor at start-up, the condition of the motor and the loading. Fluke 335, 336 and 337 clamp meters include “in-rush” current measurements as part of their characteristics.

After sticking the jaws around the input leads in one of the motors, activate the “in-rush” mode. After that, turn on the motor. The clamp meter display will indicate the maximum current drawn by the motor within the first 100 milliseconds of the total starting cycle.

Clamp meter safety

The environment for making safe measurements begins with choosing the appropriate meter for the meter where it will be used. Once the appropriate meter has been selected, you should use it following the best measurement method.

The International Electronic Technology Commission has established new safety standards for working on electrical systems. Ensure you are using a meter that meets the IEC standards and voltage rating approved for a clean environment.

For example, if necessary, to measure a voltage on an electrical panel with 480V, a third – a meter rated at 600 should be used. This means that the meter’s input circuitry is designed to withstand the voltage transients typically found in this environment without harming the user.

Selecting a meter with this rating that has a UL, CSA, VDE or TUV certificate means the meter is not only designed for IEC standards but has been individually tested and meets those standards.

Safety checklist

  • Use a meter that meets the safety standards adopted for the environment in which it will be used.
  • The test results before the measurement lead to physical damage.
  • Use the meter to test the continuity of the test leads.
  • Use only test leads for connectors and finger guards.
  • Use only meters with the recessed input jack.
  • Make sure the meter is in good operating order.
  • Always disconnect the “hot” (red) test lead first.
  • Don’t work alone
  • Use a meter that has overload protection in the ohms function.

Special features

The following special features and functions can make your clamp meter easier to use.

  • Annotator (display icon) shows at a glance what is being measured (volts, ohms, etc.)
  • Data Hold lets you freeze reading on display.
  • The one-switch operation makes it easy to select measurement functions.
  • Overload protection Both the meter and the circuit prevent damage and protect the user.
  • Automation automatically selects the same measurement range. Manual ranging allows you to lock in a certain range for repeat measurements.
  • Low battery indicator.

Independent testing is the key to safety compliance.

How can you tell if you are getting an actual Cat III or CAT II meter? Unfortunately, this is not always easy. A manufacturer can have its meters recognized as CAT II or CAT III without any independent verification.

Beware of words like “designed to meet specifications …” Designers’ plans are never a substitute for real independent testing. The IEC (International Electro-Technical Commission) develops and proposes standards but is not responsible for enforcing standards.

Look for symbols and list numbers of individual laboratories, such as UL, CSA, TEV, or other recognized authorization agencies. This mark can only be used if the product completes the agency’s test based on national/international standards.

UL 3111, for example, is based on IEC 1010. In an incomplete world, you can be sure that the multimeter you choose has been tested for safety.

Warning: Meter ratings and capacities vary by manufacturer. Before working on a new meter, be sure to inform yourself about all the meter’s operating and safety procedures in the user manual.

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