Question

Introduction, Background of Study and Theory behind Induction type Instruments

Answer 1

# Introduction:

We use induction type instrument for AC measurement only. This is because the induction phenomenon only occurs in AC. An induction instrument has multiuse. For example, we use the instruments as ammeters, voltmeters, wattmeters, and energy meters.

#Background of study:

​​​​Induction type instruments essentially have an electromagnet to produce the required magnetic field. AC in the electromagnet produces changing flux between its poles. Here, we place one aluminum disc (or aluminum drum) in the magnetic field. Hence, the changing flux links with the aluminum disc. As a result, the flux induces an eddy current on the disc. This eddy current interacts with the flux which has induced it. Consequently, there is a mechanical torque acting on the disc. This mechanical torque rotates the disc.

#Theory:

the torque produced depends on two factors. The first one is the strength of the field of the electromagnet. The second one is the value of eddy current on the disc. Of course, the torque is proportional to the strength of the magnetic field. Also, it is proportional to the eddy current. Again, the strength of the magnetic field depends on the current of the electromagnet. On the other hand, the value of eddy current depends on the strength of the magnetic field. So, we can say, the value of eddy current also depends on the current of the electromagnet.

So, the torque acting on the disc is directly proportional to the square of the current of the electromagnet. In an induction type instrument, we directly feed the measuring current into the coil of the electromagnet. Therefore, the deflecting torque is directly proportional to the square of the measuring current.

There are two type of induction instruments

(1)Ferrari’s Type Instrument

(2)Shaded Pole Type Instrument

If you need mathematical derivation or Further explanation let me know in comments. I hope you will understand this.