What is a multimeter clamp ?
A clamp multimeter is an electrical test instrument that combines a basic digital multimeter with a sensor. This sensor can be a current transformer winding or a Hall effect sensor, a Rogowski coil or an iron blade.
Clamps measure current and interfaces measure voltage test. The presence of an annular jaw in an electric meter (multimeter) allows technicians to wrap the jaws around a wire, cable or conductor. Others at any point of an electrical system that they deem appropriate to place without interruption of current and blackout circuit and check the current flow
The structure of the clamp multimeter
Inside the plastic molds of pliers multimeters, there are various circuits and parts that we will examine in order here. Flock 376 clamp multimeter
- Current jaws are hard ferrite jaws that are used to identify, focus, and measure the magnetic field generated by the current flowing through the conductor.
- Protective membrane (to protect fingers against shock)
- The data freeze button, while pressing this button, the display digits remain constant and when pressed a second time, the status returns to the original state.
- Rotary switch
- Display made of seven-segment liquid crystal LCD
- Backlight button, Min Max button and Inrush button which provides an accurate measurement of the high current with distortion entering the motor when starting work and the zero button and lever opening jaw of the current as well as the markings on the jaw for size Better grip is one of the appearance features available on the device
- Input jack and volt / ohm input jack as well as flexible current probe input are among the connectors on the device.
Internal circuit, processor and resistors are transistors, diodes and other internal components of the clamp meter, which you can see in the block diagram below the integrated performance of this equipment.
The picture below shows the real circuit and pcb of the fluke clamp multimeter. As you can see, this printed circuit board is designed in three layers and on each side there are keys to help the user. LCD, fuses , Connectors, jaw selector switch and microcontroller are the parts that you can see in the picture below
Jaw technology and pliers multimeter clamp
Clamp multimeters rely on the induction principle in a magnetic field to measure AC alternating current. By definition, an electric current passing through a wire creates a magnetic field. Because the polarity in AC current is often alternating, it causes dynamic oscillations in the magnetic field proportional to the current. The current transformer inside the clamp jaw senses magnetic fluctuations and converts this value to AC current. This type of measurement is very suitable for measuring very high AC currents passing through a semiconductor
DC current flows through a conductor with a constant polarity. As a result, the magnetic field around the conductor does not change. In this situation, ordinary receivers do not record any readings. DC clamp multimeters work on the principle of Hall effect. Hall effect sensors sense the magnetic field caused by the current flowing, which causes a low voltage in the Hall sensor. This voltage is proportional to the current, then amplified and measured.
Multimeter flexible clamp structure
Flexible clamps are known as Rogowski coils , sometimes called air-cored coils or flexible flow probes, Rogowski coils using wires and solenoids for the first time. Built and used in 1912.
Unlike current transformers and Hall effect sensors, Rogovsky coils do not have an iron core. Instead, they use a helical coil that reacts rapidly to changes (known as the first derivative) of the magnetic field of a conductor around it.
The faster the amplitude of the change, the more voltage is generated by the coil. The integrated circuit inside the device converts the measured measurements into a signal corresponding to the signal in the conductor and displays the final value on the display for the user to read.
Since Rogovsky coils do not depend on an iron core, they can be made flexible, making them easier to fit in tight spaces. This is the main feature of a flexible clamp. The absence of a magnetic core allows a wide frequency response, up to hundreds of kHz, and virtually eliminates the concerns of loading and saturation.
Because Rogovsky coils respond to signal changes, Rogovsky coils only operate on AC current.
Flexible flow multimeter probe components
According to the above cropped image:
- Exterior insulation silicone coating (red)
- A separating layer (black) of nylon material that separates the outer membrane and insulation from the inner wires of the coil.
- A thin separating layer of aluminum (white) covers the shielded outer copper wire shield
- Tightly twisted wires (blue) which are considered as Rogowski wires.
- Plastic layer of white copper core insulation
- Solid copper core insulated from flexible white pipe. The copper core strengthens the resistance of the coil against external electrical interference.
Pliers multimeters often have other sensors such as voltmeters, ohmmeters, etc., which increase the versatility of the instrument. Some types of clamp meters and multimeters also have non-contact sensors to measure voltage and even temperature.
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