How are clamp on ammeters used?

A clamp-on ammeter or simply a clamp meter’ is an instrument that is used to measure the current flowing through a conductor. An AC Clamp meter basically consists of a current transformer in its jaws, bar CT usually. Utilizing the principle of the current transformer, the reading will be displayed.

Whereas a DC clamp meter is quite different. It uses a Hall Effect sensor for measuring the current.

How Does an AC Clamp meter works?

When the instrument is ‘clamped’ on a conductor, the conductor itself acts as primary and the magnetic flux due to the current flowing through the conductor cuts the secondary of CT.

The current in the secondary of the CT is converted to voltage using a current-to-voltage converter. This signal is fed to an analog to digital converter. A microcontroller is usually employed and it will drive the display circuit for the current reading.

How Does a DC Clamp meter works?

Unlike AC, current transformers cannot be used for measuring direct current. So Hall Effect sensor is used for this purpose. The Hall element used response to the magnetic flux due to direct current in the conductor which produces a voltage across the element.

The developed voltage is proportional to the current in the conductor. So by measuring voltage, the current can be determined.

Clamp Meter Principle

Measurement Principle of AC/DC Clamp Meter

In general hall, elements are used as a sensor to detect DC current because it is not possible to employ an electromagnetic induction method as used for dedicated AC clamp meters. As shown in a figure at left, a hall element is placed across a gap created by cutting off part of the transformer jaws. When there occurs a flow of magnetic flux proportional to both AC and DC primary currents in the transformer jaws this hall element detects the magnetic flux and takes it out as an output voltage.

Hall element: This is a semiconductor to generate a voltage proportional to the product of bias current and magnetic field on the output terminal when bias current is applied to the input terminal.

How Do Clamp Meters Operate?

In general AC clamp meters operate on the principle of current transformer(CT) used to pick up magnetic flux generated as a result of current flowing through a conductor. Assuming a current flowing through a conductor to be the primary current, you can obtain a current proportional to the primary current by electromagnetic induction from the secondary side(winding) of the transformer which is connected to a measuring circuit of the instrument. This permits you to take an AC current reading on the digital display(in the case of digital clamp meters) as illustrated by the block diagram.

How does a hall effect sensor work ?

Using semiconductors (such as silicon), Hall effect sensors work by measuring the charging voltage when the device is placed in a magnetic field. In other words, once a Hall effect sensor detects that it is now in a magnetic field, it is able to sense the position of objects.

how are clamp on ammeters used ?