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

  • Rajkumar Sharma
  • 900
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  • easy
  • Tested

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.

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.MANUFACTURERSUPPLIERSUPPLIER PART NO
11CN18 PIN MALE HEADER PITCH 2.54MM WURTHDIGIKEY732-5321-ND
21CN24 PIN MALE HEADER PITCH 2.54MMDNPDNP
31CN32 PIN SCREW TERMINAL PITCH 5.08MMPHOENIXDIGIKEY277-1247-ND
43C1,C4,C50.1uF/50V SMD SIZE 0805MURATA/YAGEODIGIKEY
52C2,C30.01uF/50V SMD SIZE 0805MURATA/YAGEODIGIKEY
61D1LED SMD SIZE 0805OSRAMDIGIKEY475-1278-1-ND
73D2,D3,D41N4148 SMD MICROCHIPDIGIKEY1N4148UR-1-ND
82L1,L2FERRITE BEAD OR 100E 5% RESISTOR SMD SIZE 0805MURATA/YAGEODIGIKEY
91R1470E 5% SMD SIZE 0805MURATA/YAGEODIGIKEY
103R2,R3,R410K 5% SMD SIZE 0805MURATA/YAGEODIGIKEY
111R50E SMD SIZE 0805MURATA/YAGEODIGIKEY
121U1MAX31856MAXIMDIGIKEYMAX31856MUD+-ND
131U2LM117-3.3VTIDIGIKEYLM1117MP-3.3/NOPBCT-ND

Connections

Block Diagram

Supported Thermocouple Types

Gerber View

Photos

Video

MAX31856 Datasheet

MAX31856-555593

PCB

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