The Repulsion or Double-Iron Type is a classification of instrument used in measurement and instrumentation. This type of instrument is commonly employed in electrical measurements, particularly in the field of metrology.
In electrical measurement, the Repulsion Type instrument is used for measuring direct current (DC) or low-frequency alternating current (AC) voltages and currents. It is characterized by the presence of two iron cores, each wound with separate coils. These coils are placed in such a way that their magnetic fields repel each other when current flows through them. This repulsion force is then utilized to create a mechanical movement that is proportional to the current being measured.
Here's how the Repulsion Type instrument works:
Coil Arrangement: The instrument consists of two coils wound on separate iron cores. One coil, called the fixed coil, is connected in series with a fixed resistor and is typically connected to the source of current or voltage to be measured. The other coil, called the moving coil, is connected in parallel with a variable resistor and serves as a control coil.
Current Flow: When current flows through the fixed coil, it creates a magnetic field around the iron core. This magnetic field interacts with the magnetic field of the moving coil, resulting in a repulsive force between the coils.
Mechanical Movement: The repulsive force causes the moving coil to rotate or move against the restraining torque provided by a spring. The amount of movement is proportional to the current flowing through the fixed coil.
Pointer and Scale: The moving coil is attached to a pointer that indicates the measurement on a calibrated scale. The scale is calibrated in appropriate units (volts or amps) to provide direct readings of the measured quantity.
Repulsion Type instruments are known for their accuracy and linearity in measurements. They are often used in laboratory settings and precision applications where accurate current or voltage measurements are required. However, they can be sensitive to external magnetic fields, and care must be taken to shield the instrument from such influences.
It's important to note that while the principles described here are general to Repulsion Type instruments, there may be variations in design and construction based on the specific application and manufacturer.