Thermocouples are popular temperature measurement sensors that cover a temperature range from well below zero °C to over a thousand °C. They have good accuracy, are available in many configurations and are inexpensive. This is not to say that they are easy to use! Thermocouple are a measurement challenge:
Output levels are less than 50 mV and may be positive or negative
The “cold junction” temperature must be compensated
The output response is non-linear
Historically, measurement solutions to meet these challenges have been complex requiring several ICs and many discrete components. A few dedicated single chip solutions exist but all have shortcomings, including cost and availability.
I2C Single-Chip Solution
The TI TMP512/TMP513 Temperature and Power Supply System Monitor provides an ideal single-chip solution for thermocouple measurement. The chip features a 12-bit ADC with an input range of 40 mV that can handle bi-polar signals, and an accurate on-chip temperature sensor for reference junction compensation. Where maximum measurement accuracy is required, external PN temperature sensors may be used to measure temperature at the junction point.
I just came across an article in Sensors Magazine using a similar approach using a Dallas-Maxim 1-Wire chip desired to monitor a lithium ion battery. Functionally, the chip is very similar to the TI TMP513 but it uses the 1-Wire bus instead of I2C. This is a nice option when you want to use several sensors spread over a wide area.
Each 1+Wire device, just like I2C devices, has unique resisters which must be read and understood to calculate the measurement value. The 1-Wire protocol is the same for all 1-Wire devices, but the communication is unique to each device.
One other point to make in comparing these two solutions: The DS2762 is great for communicating over long distances compared to the short distances possible with an I2C interface. But you pay for this ability. The Maxim part is over $12 in small quantity, the TI part is less than $4.
Re: A Thermocouple Measurement Circuit with Swordfish Softwa
6 years 5 months ago #12901