System Board 6661

MAXREFDES1154: Configurable 4-Channel RTD/TC Measurement System Using the MAX11410

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

The MAXREFDES1154 provides a complete system solution for highly accurate temperature measurement in industrial applications. Analog front end includes two 8:1 multiplexer MAX4617 and one 4:1 multiplexer MAX4704 for RTD/TC input selection, and one 24-bit, 10-channel ADC MAX11410.

The microcontroller on board is used to communicate with the MAX11410 ADC, control the multiplexers, and process the ADC conversion results. The 24V field input power supply is isolated from both the analog front end and the microcontroller, which is powered using a USB. Isolation enhances system robustness, an important consideration in harsh industrial applications.

The MAXREFDES1154 design integrates two 8:1 multiplexer (MAX4617) and one 4:1 multiplexer (MAX4704), a 24-bit 10-channel ADC with internal PGA buffers (MAX11410), a high-precision 1.250V voltage reference (MAX6071), 2.75kVRMS digital isolator (MAX14930 and MAX14931), a STM32F1 microcontroller, a μP supervisor (MAX6730), a FTDI USB-UART bridge, a high-efficiency Iso-Buck DC-DC converter (MAX17681), and an isolated/regulated +3.3V power rail (MAX16910). The entire system typically consumes less than 300mW and fits onto a 5cm x 9cm board. It is targeted for industrial PLC applications.

Key Features

  • Highly accurate measurement
  • Four channels
  • Each channel can be configured as either RTD or TC input
  • Supports 2-wire and 3-wire RTD
  • Supports all types of thermocouple
  • Thermocouple with RTD for cold junction compensation
  • Sensor open detection
  • 24V input protection
  • Isolated power and data
  • Board-level calibration
MAXREFDES1154 Hardware Enlarge+

This board is not available for purchase.

Designed, Built, Tested

Describing both hardware and firmware, this document details system design, particularly how the analog front end is achieved. This reference design has been built and tested, details of which follow later in the document.

Design Resources


24-Bit Multi-Channel Low-Power 1.9ksps Delta-Sigma ADC with PGA

  • High Resolution And Low Noise For Signal Sources With Wide Dynamic Range
  • Optimized Features For More Efficient System Design
  • Low Power for Efficient Systems

4-Channel, 1kVRMS, 2.75kVRMS, and 3.75kVRMS Digital Isolators

  • Robust Galvanic Isolation of Digital Signals
  • Interfaces Directly with Most Micros and FPGAs
  • Many Options Support Broad Applications

4-Channel, 1kVRMS, 2.75kVRMS, and 3.75kVRMS Digital Isolators

  • Robust Galvanic Isolation of Digital Signals
  • Interfaces Directly with Most Micros and FPGAs
  • Many Options Support Broad Applications

4.5V to 42V Input, High-Efficiency, Iso-Buck DC-DC Converter

  • Reduces External Components and Total Cost
  • Reduces Number of DC-DC Regulators to Stock
  • Reduces Power Dissipation

200mA, Automotive, Ultra-Low Quiescent Current, Linear Regulator

  • Enables System Designers to Meet Stringent Module Requirements for 100μA Quiescent Current
  • Tiny Output Capacitors Reduce Board Space and BOM Cost
  • Accurate Active-Low RESET Output with Adjustable Delay Eliminates Need for Separate Reset IC

Single-/Dual-/Triple-Voltage µP Supervisory Circuits with Independent Watchdog Output

  • VCC1 (Primary Supply) Reset Threshold Voltages from +1.575V to +4.63V
  • VCC2 (Secondary Supply) Reset Threshold Voltages from +0.79V to +3.08V
  • Adjustable RSTIN Threshold for Monitoring Voltages Down to +0.63V (MAX6734/MAX6735 Only)

Low-Voltage, 60Ω, 4:1 Analog Multiplexer in QFN

  • 3mm x 3mm 12-Pin QFN Package
  • Guaranteed On-Resistance:
  • Guaranteed Match Between Channels: 3Ω (max)

High-Speed, Low-Voltage, CMOS Analog Multiplexers/Switches

  • Fast Switching Times
  • Pin Compatible with Industry-Standard 74HC4051/74HC4052/74HC4053 and MAX4581/MAX4582/MAX4583
  • Guaranteed On-Resistance