Definition
A current clamp is an instrument used to measure the number of amperes passing through a conductor. The electrical device comes with jaws that open when brought close to the electrical conductor to allow it to clamp. This feature eliminates the need for the current clamp to make physical contact with the current-conducting wire or rod or any other object to measure the flowing currents. Additionally, it does not need any sort of disconnection to insert through the probe.
Also referred to as a current probe or current meter, current clamps find application in the computation and quantification of the magnitude of a conductor’s alternating current (AC). They can also measure the waveform and phase when combined and used with other instruments.
A few types of current clamps can assess the direct current (DC) flowing through the conductors. They primarily include the vane and hall effect ones.
Classification of Current Clamps
Current clamps can be of different types based on their structure, construction, and application. Each kind has its unique features and finds application in specific fields and areas.
The classification of current clamps comprises of the following:
Current Transformer
A current transformer is a common and widely used form and version of a current clamp. It consists of a split ring composed of soft iron or ferrite. It has a wire coil that comes wound around one or two halves to form one winding of the electrical device. The other winding gets comprised by the conductor to which the current transformer remains clamped around.
Similar to all other transformers, a current transformer works solely on pulse waveforms and alternating currents. During current measurement, the conductor serves as the primary winding and the coil, the secondary winding.
The reverse is also feasible and gets used essentially to infuse current into the conducting material. In such cases, the coil takes over the place and role of the conductor and becomes the primary coil. The vice versa ensues for the secondary coil. This mode finds application in the susceptibility testing of electromagnetic compatibility where an interference current gets injected or introduced.
Iron Vane
An iron vane type of current clamp allows the measurement of both alternating and direct current. It consists of an iron vane that moves continually and gets affected by the magnetic flux operating in the core. These instruments proffer the “true” value of the Root Mean Square (RMS) for non-sinusoidal alternating current waveforms.
Iron vane current clamps get used predominately in a moving pointer or analog clamp meter. It comes fixed to the display mechanism of the device. However, particular restrictions get imposed due to the physical size of these types of current clamps. For example, the frequencies of the power transmission get limited to around 100 Hz only.
Hall Effect
A hall effect current clamp also finds application in the measurement of both direct and alternating currents. Nevertheless, they are a more sensitive type. They can take the assessment of the values with the frequencies in the kilohertz range.
In the olden days, this type got utilized with oscilloscopes often. With the advent of technology in modern times and the invention of computerized and high-end digital multimeters, hall effect current clamps are gradually becoming commonplace devices.
Rogowski Coil
A Rogowski coil is a current sensor or a coreless transformer used in power monitoring loggers and clamp meters. This type is flexible and comes with better linearity due to the absence of a core that would otherwise have required saturation. It does not need the contact of any electrical or magnetic field at the opening.
Rogowski coils provide a voltage that remains proportional to the rate of change of the primary cable current. Hence, it requires more processing for the signal before the sensed values can get displayed.
Parts or Components of a Current Clamp
Irrespective of the type of current clamp, the parts of the device remain consistent. They comprise of the following:
- Transformer Clamps or Jaws: The jaws or transformer clamps get used for sensing and discovering the magnetic field during the operation of the current clamp. It ensues while the current continues to flow in the conductor.
- Clamp Opening Trigger: The clamp opening trigger closes or opens the instrument’s clamps.
- Power Switch: The power switch gets used for switching the current clamp off or on.
- Back Light Button: The backlight button helps to activate the display. It aids in reading the presented data or value on the screen in dimly lit or dark places.
- Hold Button: The hold button retains the final obtained value on the display.
- Ground or Negative Input Terminal: The ground or negative input terminal connects the negative terminal or ground jack.
- Positive Input Terminal: The positive input terminal connects the positive terminal or jack of the current clamp.
- Display: The display or LCD shows the measured and estimated values.
- Functional Rotary Switch: The functional rotary switch chooses the type of current clamp and the range of measurable current.
Benefits of a Current Clamp
A current clamp comes with numerous advantages that make it a beneficial and convenient electrical device. A few of them entails the following:
- It can come into use in environments and surroundings with noisy and high electrical disturbances.
- It can measure the current flow in an active and live conductor without cutting off the power supply.
- It has an ergonomic design that can fit into the hand seamlessly. It stands true even with protective gear.
- It can take measurements in constricted and narrow places that require a lucid estimate with high accuracy.
- It proffers a wide range of quantifications in a short amount of time, saving both money and effort.
- It is compact and lightweight and can get carried or stored in a toolbox effortlessly. When used, it does not exert any strain or pressure on the hands.
- It can substitute a multimeter where splitting the connection or circuit is not feasible. It is primarily because contact during the measurement becomes safe.
Drawbacks of a Current Clamp
Like all other things, a current clamp has its fair share of disadvantages. Although they do not hamper the overall performance and reputation of the device, they may become a source of decreased use for the instrument.
A few of such drawbacks of a current clamp include the following:
- It comes with lesser features compared to a multimeter. It does not have the to measure frequency and temperature.
- Most current clamps do not have adequate damage protection. Hence, they are susceptible to even the smallest of dents or scratches that can impair their function.
