Servo-sensed-heater-protector

Description: This circuit responds quickly enough to prevent damage from most overloads. Capacitor C1's input is connected to the output of the LT1088 servo circuit. If the LT1088 circuit's output exceeds the threshold at C1's other input, C1 trips, discharging the 2-µF capacitor. This causes C2's output to become low, energizing the relay and breaking the heater circuit. The 560-kΩ resistor provides a long recharge for the capacitor, preventing chattering action. The speed of response for this arrangement is limited by the circuit's slew rate, which is approximately 0.2 V/ms. For reasonable overloads, the LT1088's temperature increases by about 1 °C/ms. A 10-V LT1088 output step takes 50 ms, resulting in a temperature rise of about 50 °C.

This circuit operates as an overload protection mechanism utilizing the LT1088 servo amplifier. The primary function of the circuit is to monitor the output voltage of the LT1088. Capacitor C1 is strategically placed to detect when the output voltage exceeds a predetermined threshold. When this occurs, C1 discharges, which triggers the relay mechanism that interrupts the heater circuit, thereby preventing potential damage due to overheating.

The design includes a 2-µF capacitor (C1), which plays a critical role in the rapid response of the circuit. The discharging of this capacitor leads to a low output at C2, which is responsible for activating the relay. The relay serves as a switch that disconnects the heater from the power supply, ensuring that the heater does not operate under unsafe conditions.

The 560-kΩ resistor is essential for controlling the recharge time of C1, which helps to mitigate any chattering effects that could occur due to rapid fluctuations in voltage. This resistor ensures that the capacitor has a longer time to recharge before it can trip again, thus stabilizing the operation of the circuit.

The response time of the circuit is inherently limited by the slew rate of the LT1088, which is approximately 0.2 V/ms. This means that for every millisecond, the output voltage can change by 0.2 volts. In practical terms, for a significant overload, the LT1088's temperature will rise approximately 1 °C for each millisecond, indicating the thermal response of the circuit under load conditions. When subjected to a 10-volt step change at the output, the LT1088 takes about 50 milliseconds to stabilize, leading to a corresponding temperature increase of about 50 °C.

Overall, this circuit presents an effective solution for overload protection in heating applications, combining timely response with reliable operation to safeguard against thermal damage.This circuit responds quickly enough to prevent damage from most overloads. C 1 "s input is connected to the output of the LT1088 servo circuit. If the LT1088 circuit"s output exceeds the threshold at Cl"s other input, C1 trips, discharging the 2-!"F capacitor. This causes C2"s output to become low, energize the relay, and break the heater circuit. The 560-KO resistor provides a long recharge for the capacitor, preventing chattering action. This arrangement"s speed of response is limited by the rrns circuit"s slew rate, about 0.2 V/ms. For reasonable overloads, the LT1088"s temperature increases about 1 °C/ms. A 10-V LT1088 output step takes 50 ms, causing a temperature rise of about 50°C.