The transformers which are particularly designed to provide electrical isolation between primary and secondary circuits, without a change in voltage and current level are called isolation transformers.
The turns ratio of such isolation transformers is 1:1 i.e N1 and N2. Hence, isolation transformers are also called 1:1 transformers.
The isolation transformer greatly reduces any voltage spikes that originate on the supply side before they are transferred to the load side. Some isolation transformers are built with a turns ratio of 1:1. A transformer of this type has the same input and output voltages and is used for the purpose of isolation only. The main function of the isolation transformer is to reduce the voltage spike before it reaches the load.
In the PMMC type instrument, the deflection is directly proportional to the current flowing through the instrument, we get a uniform scale for the instrument. It gives a uniform scale of upto 270° or more.
Td ∝ I