Precision Thermocouple Amplifier (Thermocouple to Digital Converter with Linearization – SPI Interface)

Rajkumar Sharma
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SKU: EL111499
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This precision thermocouple sensor module performs cold-junction compensation and digitizes the signal from any type of thermocouple. The output data is formatted in degrees Celsius. The converter resolves temperatures to 0.0078125°C, allows readings as high as +1800°C and as low as -210°C (depending on thermocouple type), and exhibits thermocouple voltage measurement accuracy of ±0.15%. The thermocouple inputs are protected against overvoltage conditions up to ±45V. A lookup table (LUT) stores linearity correction data for several types of thermocouples (K, J, N, R, S, T, E, and B). Line frequency filtering of 50Hz and 60Hz is included, as well as thermocouple fault detection. An SPI-compatible interface allows the selection of thermocouple type and setup of the conversion and fault detection processes. The operating supply of the project is 5V and it consumes a very low current. The module communicates over the SPI interface.

Arduino Interface

Testing this module with Arduino is very easy. The pin configuration information is available below.

Adafruit library and example code are available at the Adafruit website below and on downloads under the article.

https://learn.adafruit.com/adafruit-max31856-thermocouple-amplifier/wiring-and-test

Arduino Connection to board CN1

CN1 Pin 1 >> 5V
CN1 Pin 2 >> DY DIGITAL PIN D5
CN1 Pin 3 >> CS DIGITAL PIN D10
CN1 Pin 4 >> SK DIGITAL PIN D13
CN1 Pin 5 >> SO DIGITAL PIN D12
CN1 Pin 6 >> SI DIGITAL PIN D11
CN1 Pin 7 >> FAULT NO CONNECTION
CN1 Pin 8 >> GND

Features

Supply 5V DC @ 10mA
Supports K, J, N, R, S, T, E, and B Type Thermocouples
Easy SPI Interface
Screw Terminal for Easy Sensor Connections
Male Header Connector for Micro-Controller Connections
On-Board Power LED
Detects Open Thermocouples
Over- and Under temperature Fault Detection
Provides High-Accuracy Thermocouple Temperature Readings
Includes Automatic Linearization Correction for 8 Thermocouple Types
±0.15% (max, -20°C to +85°C) Thermocouple Full- Scale and Linearity Error
19-Bit, 0.0078125°C Thermocouple Temperature Resolution
Internal Cold-Junction Compensation Minimizes System Components
±0.7°C (max, -20°C to +85°C) Cold-Junction Accuracy
±45V Input Protection Provides Robust System Performance
Simplifies System Fault Management and Troubleshooting
50Hz/60Hz Noise Rejection Filtering Improves System Performance
PCB dimensions: 21.59 x 33.81 mm

Schematic

Parts List

NO.	QNTY.	REF.	DESC.	MANUFACTURER	SUPPLIER	SUPPLIER PART NO
1	1	CN1	8 PIN MALE HEADER PITCH 2.54MM	WURTH	DIGIKEY	732-5321-ND
2	1	CN2	4 PIN MALE HEADER PITCH 2.54MM	DNP		DNP
3	1	CN3	2 PIN SCREW TERMINAL PITCH 5.08MM	PHOENIX	DIGIKEY	277-1247-ND
4	3	C1,C4,C5	0.1uF/50V SMD SIZE 0805	MURATA/YAGEO	DIGIKEY
5	2	C2,C3	0.01uF/50V SMD SIZE 0805	MURATA/YAGEO	DIGIKEY
6	1	D1	LED SMD SIZE 0805	OSRAM	DIGIKEY	475-1278-1-ND
7	3	D2,D3,D4	1N4148 SMD	MICROCHIP	DIGIKEY	1N4148UR-1-ND
8	2	L1,L2	FERRITE BEAD OR 100E 5% RESISTOR SMD SIZE 0805	MURATA/YAGEO	DIGIKEY
9	1	R1	470E 5% SMD SIZE 0805	MURATA/YAGEO	DIGIKEY
10	3	R2,R3,R4	10K 5% SMD SIZE 0805	MURATA/YAGEO	DIGIKEY
11	1	R5	0E SMD SIZE 0805	MURATA/YAGEO	DIGIKEY
12	1	U1	MAX31856	MAXIM	DIGIKEY	MAX31856MUD+-ND
13	1	U2	LM117-3.3V	TI	DIGIKEY	LM1117MP-3.3/NOPBCT-ND