Precision thermocouple amplifier

Analog Devices MAX31856

Common view of the Precision Thermocouple Amplifier board.
Figure 1. Common view of the Precision Thermocouple Amplifier board.

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 ±45 V. 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 50 Hz and 60 Hz 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 5 V and it consumes a very low current. The module communicates over the SPI interface.

China PCB Prototype and Fabrication Manufacturer

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 >> DRDY DIGITAL PIN D5
CN1 Pin 3 >> CS DIGITAL PIN D10
CN1 Pin 4 >> SCK DIGITAL PIN D13
CN1 Pin 5 >> SDO DIGITAL PIN D12
CN1 Pin 6 >> SDI DIGITAL PIN D11
CN1 Pin 7 >> FLT
CN1 Pin 8 >> GND

Features

  • Supply 5 V DC @ 10 mA
  • 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 hermocouple 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
  • ±45 V Input Protection Provides Robust System Performance
  • Simplifies System Fault Management and Troubleshooting
  • 50 Hz/60 Hz Noise Rejection Filtering Improves System Performance
  • PCB dimensions: 21.59 × 33.81 mm

Schematic

Circuit of the Amplifier.
Figure 2. Circuit of the Amplifier.

Connections

External connections.
Figure 3. External connections.

Block diagram

Block diagram.
Figure 4. Block diagram.

Supported thermocouple types

Table 1. Supported thermocouples
Type T-wire T+wire Temp range Nominal
sensitivity (pV/X)
Cold-junction
temp range
B Platinum/Rhodium Platinum/Rhodium 250 °C to 1820 °C 10.086
(+500 °C to +1500 °C)
0 to 125 °C
Е Constantan Chromel –200 °C to +1000 °C 76.373
(0 °C to +1000 °C)
–55 °C to +125 °C
J Constantan Iron –210 °C to +1200 °C 57.953
(0 °C to + 750 °C)
–55 °C to +125 °C
К Alumel Chromel –200 °C to +1372 °C 41.276
(0 °C to + 1000 °C)
–55 °C to +125 °C
N Nisil Nicrosil –200 °C to +1300 °C 36.256
(0 °C to +1000 °C)
–55 °C to +125 °C
R Platinum Platinum/Rhodium –50 °C to +1768 °C 10.506
(0 °C to +1000 °C)
–50 °C to +125 °C
S Platinum Platinum/Rhodium –50 °C to +1768 °C 9.587
(0 °C to +1000 °C)
–50 °C to +125 °C
Т Constantan Copper –200 °C to +400 °C 52.18
(0 °C to +400 °C)
–55 °C to +125 °C

Photos

Back side of the board.
Figure 5. Back side of the board.

Downloads

  1. Project files

Materials on the topic

  1. Datasheet Texas Instruments LM1117
  2. Datasheet Analog Devices MAX31856

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