Temperature protection for resistive high-power loads

The circuit shown in here has been designed to protect (expensive) high-power resistors against overheating. Very high power resistors (of the order of 50 watts or more) are used in electronics laboratories and workshops to test audio amplifiers, power supplies and the like. To assist in their cooling, high-power resistors often come fitted on a heatsink. Since they are not cheap, It stands to reason that damage as a result of overheating must be prevented. This can be achieved at a small outlay by the present circuit, which sounds a buzzer if the heatsink temperature reaches a critical level. Provided the guard is supplied by the mains, a pair of fans is then switched on to assist in the cooling of the power resistors.