MAXREFDES1154: Configurable, quad-channel, RTD/TC measurement system based on the MAX11410

The MAXREFDES1154 is a configurable, 4-channel, RTD/TC measurement system. Each channel can be configured as RTD input or TC input, and RTD is used for cold junction compensation. The RTD can be a PT100 or PT1000, supporting 2-wire or 3-wire connections. The same configuration can also be used to measure resistance. MAXREFDES1154 supports all types of thermocouples and uses RTD for cold junction compensation. It can be PT100 or PT1000, but it needs to be configured as a 2-wire connection.

MAXREFDES1154 provides a complete system solution for high-precision temperature measurement in industrial applications. The analog front end includes two 8:1 multiplexers MAX4617 and a 4:1 multiplexer MAX4704 (used to select RTD/TC inputs), as well as a 24-bit, 10-channel ADC MAX11410 for digital conversion.

Use the onboard microcontroller to communicate with the MAX11410 ADC, control the multiplexer, and process the ADC conversion results. The 24V field input power is isolated from the analog front-end and microcontroller power supplies, which are powered by USB. Isolation increases system robustness and is an important consideration in harsh industrial applications.

The MAXREFDES1154 design includes two 8:1 multiplexers (MAX4617) and one 4:1 multiplexer (MAX4704), 24-bit 10-channel ADC with internal PGA buffer (MAX11410), high-precision 1.250V Voltage reference (MAX6071), 2.75kVRMS digital isolator (MAX14930 and MAX14931), STM32F1 controller, μP supervisory circuit (MAX6730), FTDI USB-UART bridge, high-efficiency Iso-Buck DC-DC converter (MAX17681), and +3.3 V isolated/regulated power supply (MAX16910). The entire system consumes typically less than 300mW and is mounted on a 5cm x 9cm board, making it ideal for industrial PLC applications.

Key Features

• High-precision measurement

• Four channels

• Each channel can be configured as RTD or TC input

• Supports 2-wire and 3-wire RTDs

• Supports all types of thermocouples

• Thermocouple with RTD for cold junction compensation

• Sensor open circuit detection

• 24V input protection

• Isolate power and data

• Board level calibration

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Design, build and test

This document describes the hardware and firmware and provides detailed system design, specifically how to implement the analog front end. The reference design has been built and tested, please refer to this document for details.

design resources