Both these instruments are commonly used for indicating and measuring purposes. The difference between moving coil and moving iron instrument is discussed in this article.
Table of Contents
Moving iron instrument
Its name speaks for itself. Moving iron instrument means the moving part is an iron piece (soft iron piece basically).
It works on the principle that the electromagnet produces a magnetic field, which attracts or repels the soft iron piece.
MI instrument is classified into two types one is attraction type and another is repulsion type.
Attraction type MI instrument works on the principle of attraction of the iron piece
Repulsion type MI instrument works on the principle of repulsion between the two iron pieces
Moving coil instrument
As its name suggests in this instrument a coil moves and produces deflection.
The moving coil instruments work on the principle that, when a current-carrying is placed in the field of the permanent magnet. A torque is exerted on the coil.
PMMC is an example of a moving coil instrument.
Difference between moving coil and moving iron instrument
| Moving iron | Moving coil |
| It works on the principle of magnetism | The working principle of this instrument is similar to the DC motor |
| The soft iron piece is used as rotating elements | The coil is used as a rotating element |
| Basic range: 10mA-100A | Basic range: 10µ -100mA |
| It can be used with both AC and DC | It can be used only with DC |
| Deflection is proportional to the square of the current | Deflection is proportional to current |
| Controlling torque is produced by gravity | Spring produces the controlling torque |
| It uses air damping | It uses eddy current damping |
| It has a non-uniform scale | It has a uniform scale |
| This instrument consumes high power | The power consumption of these instruments is low |
| It is less accurate but if designed properly it can be very accurate | The accuracy of this instrument is very good for dc measurement |
| It is not the very sensitive instrument | It is a very sensitive instrument |
| It is not an expensive instrument | It is an expensive instrument |
| Moving iron instrument used as an indicating instrument | Moving coil instrument used as a measurement instrument |
Key difference between moving coil and moving iron instrument.
Quick summary
- The basic difference between moving coil and moving iron instrument is MI instrument works on magnetism principle and moving coil instrument works on the principle similar to DC motor.
- MI instrument used as indicating instrument and the moving coil instrument used for measuring purpose.