Thermal system with a temperature limiting device

A thermal system comprising:

• a two-wire heater including two terminals;
• a process controller configured to control thermal performance of the two-wire heater based on data from one or more discrete sensors;
• a power switch operable to provide power to the two-wire heater based on a control signal from the process controller;
• and
• a temperature limiting device separate from the process controller, wherein the temperature limiting device comprises:
• a modular unit that comprises:
• a heater interface configured to connect to a two-wire heater of the thermal system;
• a power interface configured to connect to a power source to receive power;
• an input/output interface configured to communicate with the process controller;
• and
• a controller including a sensor circuit, wherein:
• the sensor circuit is configured to measure an electrical characteristic of the two-wire heater, wherein the electrical characteristic includes voltage, current, or a combination thereof,
• the controller is configured to calculate a temperature of the thermal system based on the measured electrical characteristic, an offset, and a temperature based on the two-wire heater and determine whether the temperature is greater than a temperature setpoint, and
• the controller is configured to operate the power switch to turn-off power to the two-wire heater in response to the temperature of the thermal system being greater than the temperature setpoint.

A temperature limiting device for a thermal system, the temperature limiting device comprising:

• a modular unit comprising:
• a heater interface configured to connect to a two-wire heater of the thermal system;
• a power interface configured to connect to a power source to receive power;
• a power switch disposed between the heater interface and the power interface to control power to the two-wire heater;
• an input/output interface configured to communicate with one or more external devices, wherein the one or more external devices includes a process controller of the thermal system;
• and
• a controller including a sensor circuit, wherein:
• the sensor circuit is configured to measure an electrical characteristic of the two-wire heater, wherein the electrical characteristic includes voltage, current, or a combination thereof, and
• the controller is configured to calculate a temperature of the thermal system, wherein the calculation is based on a change in the measured electrical characteristic and predefined heater information, determine whether the temperature is greater than a temperature setpoint, and turn off power to the two-wire heater via the power switch in response to the temperature of the thermal system being greater than the temperature setpoint.