Description
The MAX31855 Thermocouple Module is a cold-junction compensated K-type thermocouple-to-digital converter designed for high-temperature measurement in appliances, HVAC systems, automotive, and industrial equipment . It performs cold-junction compensation and digitizes the thermocouple signal internally, outputting a signed 14-bit temperature value via a read-only SPI-compatible interface .
The converter resolves temperature to 0.25°C and can read as high as +1800°C and as low as -270°C, with K-type accuracy of ±2°C over -200°C to +700°C . The device includes fault detection for thermocouple shorts to GND or VCC, as well as open thermocouple detection . Breakout modules typically add a screw terminal for the thermocouple and 0.1″ header pins for Arduino connection.
Critical limitations: The MAX31855 does not perform linearization—thermocouple results are inherently non-linear, and greater accuracy requires external NIST linearization calculations . It is designed for ungrounded thermocouples; grounded thermocouples may cause errors . The SPI interface must not exceed 4.0V, even on 5V systems—use level shifting if necessary . Conversion takes 70–100ms, limiting sampling to approximately 10–14 samples per second .
Features
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Direct K-Type Thermocouple Interface: Integrates cold-junction compensation and digitization in one IC .
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14-Bit, 0.25°C Resolution: Fine-grained temperature readings .
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SPI-Compatible Read-Only Interface: Simple connection to any microcontroller .
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Fault Detection: Flags thermocouple shorts to GND/VCC and open thermocouple conditions .
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Wide Temperature Range: Reads up to +1800°C (accuracy specified to +700°C for K-type) .
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Negative Temperature Support: Unlike the older MAX6675, reads down to -270°C .
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Low Power Consumption: Operates from 3.0V to 5.5V .
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Compact 8-Pin SO Package: Small footprint for space-constrained designs .
Technical Specifications
| Parameter | Specification |
|---|---|
| Sensor Type | K-type thermocouple-to-digital converter |
| Temperature Range | -270°C to +1800°C (K-type) |
| Resolution | 14-bit, 0.25°C |
| Accuracy (K-type) | ±2°C (-200°C to +700°C) |
| Supply Voltage | 3.0V to 5.5V |
| Interface | SPI-compatible (read-only) |
| Conversion Time | 70–100ms typical |
| Package | 8-pin SO (IC); breakout module varies |
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