It is used to measure rise in temperature at various points as mentioned in standard at junctions.
The set-up consists of a Thyristorized (Solid state controlled) Current Source (to maintain the Current even as impedance of the cable changes due to rapid temperature rise), a specially designed step down transformer system, PC based control system, Temperature data logging on PC, Servo-Controller and other indications. Digital voltmeter Primary Voltage indicates the position of auto transformer (variac).
Servo controlled mechanism is used to maintain constant current throughout the test in manual mode. CR/AL('K' type) type thermocouples are used for temperature sensing.