Thermocouple Solutions
A thermocouple is a rugged temperature sensor used to measure high temperatures. When the thermocouple Hot-Junction is exposed to high temperatures such as 1000ºC, a small change in voltage can be measured at the open end of the thermocouple. Meanwhile, the Cold-Junction is normally at room temperature.
The thermocouple wires are made of two dissimilar materials, typically categorized by either base metal or precious metal compositions. There are several types of thermocouple standards and the most common types are type K and type J thermocouples. Additional thermocouples, such as type T, N, S, B, and R, are application-specific and provide increased sensitivity at various temperature ranges.
Common applications for thermocouples include petrochemicals, industrial ovens, engines, and machinery used in the steel and iron industry with operating ambient temperatures ranges of approximately –200ºC to 2000ºC.
Microchip offers a plug-and-play integrated solution for common thermocouples, the MCP9600 family. This family of devices integrates the thermocouple error compensation equation and the cold-junction compensation sensor with a factory-calibrated hot-junction accuracy of ±1.5ºC, ±4ºC, and ±8ºC maximum accuracy for high, medium, and low accuracy applications.
In addition, the device provides various user-programmable features for embedded applications such as open-circuit and short-circuit detection, four user-programmable temperature alert limits, temperature averaging, programmable temperature resolution, and power-saving features such as burst-mode temperature sampling.
Microchip offers an evaluation board for the MCP9600 which allows users to evaluate the various features. Microchip also provides a number of precision linear products, such as op-amps and instrumentation amplifiers, MCP6V01 and MCP6N11, respectively. Additionally, Microchip provides high-resolution delta-sigma Analog-to-Digital Converters (ADCs) for thermocouple solutions such as the MCP3461 16-bit, MCP3421 18-bit, and MCP3465 24-bit ADCs.
One of the unique advantages of thermocouples is the fast thermal response characteristics with a typical response time of approximately 5 ms. A typical application for such highspeed response is electrical arcing for industrial or high current breaker switches, and the MCP6V01 family op amps are ideal solutions for such applications (see the application note, "Thermocouple Circuit Using MCP6V01 and PIC18F2550," from Microchip for details).