What device is used to measure the current flowing in a motor circuit by sensing the heat generated?

The device used to measure the current flowing in a motor circuit by sensing the heat generated is a thermal overload. This device operates by monitoring the temperature of the windings in a motor. As electrical current flows through the motor, it generates heat due to resistance. The thermal overload is typically designed to trip or interrupt the circuit if the temperature exceeds a certain threshold, which indicates that the current may be too high and could potentially damage the motor.

Thermal overloads serve as a protective measure, ensuring that the motor operates within safe thermal limits. If the current increases, the corresponding heat build-up will cause the thermal overload to activate, thus disconnecting the circuit and preventing overheating that can lead to insulation failure or other damage. This makes thermal overloads essential for the safety and longevity of electric motors.

In contrast, the other options like a limit switch, logic gate, and diode serve different functions and do not measure current through heat generation. Limit switches are used for position detection, logic gates perform logical operations in circuits, and diodes allow current to flow in one direction only, but none of them provide a measurement of current through the principle of heat sensing.