TMPSNSRD-TCPL1: Thermocouple, 18-bit Res, USB, I2C

The Thermocouple Reference Design demonstrates how to instrument a Thermocouple and accurately sense temperature over the entire Thermocouple measurement range.

This solution uses the MCP3421 18-Bit Analog-to-Digital Converter (ADC) to measure voltage across the Thermocouple. The ADC has an internal 2.048V reference voltage and a Programmable Gain Amplifier with 1, 2, 4, 8V/V. At a Gain of 8V/V the PGA effectively adds 3LSb to the ADC. This increases the ADC resolution to 21-bit or 2 µV/LSb. Therefore, the Thermocouple EMF voltage is measured with 2 µV resolution. For K-type Thermocouple, measurement system provides a ±0.05°C resolution. The cold-junction compensation is done using a ±1°C accurate 0.0625°C resolution silicon temperature sensor, the MCP9804.

This solution provides a reliable and accurate Thermocouple instrumentation without the need for extensive circuit compensation and calibration routines. The ADC output is read using a PICmicro Microcontroller. This controller is also connected to a PC using USB interface. The Thermal Management software is used to plot the Thermocouple temperature data in stripchart format.

The Thermocouple Reference Design has the following features:

• K-type Thermocouple
  
• Thermocouple connector
  
• Thermal Management GUI
  
• MCP9804 Temperature sensor with ±0.25°C (typical) accuracy from -40°C to +125°C
  
• 18-Bit ADC MCP3421
  
• PIC18F2550 PIC® Microcontroller
  
• USB interface to PC