THERMOCOUPLE
REFERENCE DESIGN
© 2010 Microchip Technology Inc. DS51889A-page 11
Chapter 2. Installation and Operation
2.1 INTRODUCTION
The Thermocouple Reference Design demonstrates Microchip’s solution to accurately
measure temperature using a Thermocouple and an 18-bit ADC, MCP3421. This
solution eliminates the need for the traditional analog instrumentation system
calibration or gain and offset trimming techniques. In addition, the Thermocouple
linearization techniques can be implemented in firmware or software.
The Thermocouple Reference Design allows user to evaluate Microchip’s solution to
accurately measure the temperature. When measuring temperature using a
Thermocouple cold junction compensation is critical. It provides a reference to the
thermocouple measurement. The MCP9804 provides the cold junction compensation
at ±1°C accuracy. If the Thermocouple is compensated using the compensation
equation provided by National Institute of Standards and Technology (NIST ITS-90),
then temperature can be measured with ±1°C accuracy over the entire measurement
range.
The MCP3421 and the MCP9804 serial output lines are connected to a PICMicro
Microcontroller. This controller communicates with a PC via the USB interface and
commands the ADC to convert voltage. The serial data is then displayed on the PC
using the Thermal Management software in stripchart format.
2.2 FEATURES
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
