One wire thermocouple sensor

Paul Boughton

Maxim Integrated Products has combined one wire thermocouple sensor with the digital conditioning and conversion for the first time to simplify medical and industrial sensor designs.

“Accurate temperature measurement is critical in industrial and medical equipment,” said Susie Inouye, Research Director at Databeans. “Products that enable high accuracy temperature sensing will become increasingly important for these industries.”

The MAX31850/MAX31851 cold-junction-compensated, 1-Wire  thermocouple-to-digital converters achieve ±2.0°C accuracy (not including sensor nonlinearity) while integrating all of the functions required for a complete thermocouple-to-digital solution.

The 1-Wire interface allows multiple sensor locations to communicate and draw power over a single data line, greatly simplifying wiring requirements. Designers can use the MAX31850 or MAX31851 instead of multiple discrete components for accurate temperature measurement in medical, industrial, and solar applications.

Because thermocouple output voltages are small and cold-junction compensation is needed to achieve accurate results, the digitization of thermocouple signals can be a challenge.

The MAX31850/MAX31851 are the industry’s first solution to integrate a discrete analogue-to-digital converter (ADC), a highly accurate reference, a temperature sensor for cold-junction compensation, and a 1-Wire bus interface into a single chip.

“The digitisation of thermocouple signals poses a unique design challenge, especially when a large number of thermocouples are involved,” said Amy Gebrian, Senior Business Manager of Thermal Management Products at Maxim Integrated. “The MAX31850/MAX31851 greatly ease design effort and minimise system wiring by integrating a complete thermocouple digitizer circuit and a single wire interface into one IC.”

The converters operate with several types of thermocouples, speeding system design, lowering system cost, and reducing the bill of materials (BOM). The MAX31850/MAX31851 also identify open or shorted thermocouples that could result in erroneous temperature readings or system faults. A microcontroller can read the fault status at any time to help ensure uptime and prevent costly repairs.

The 1-Wire interface allows for a large number of devices on the same communication bus. The four dedicated address pins uniquely identify up to 16 sensor locations.

The MAX31850 is available for K, J, N, T, and E thermocouple types and the MAX31851 is available for R and S thermocouple types.
The converters are available in a 10-pin, exposed-pad TDFN package (3 mm x 4 mm x 0.75 mm) and specified over the -40 °C to +125 °C temperature range.

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