Precision Temperature Measurement System

The achievable accuracy depends on sensor type and configuration: RTDs (PT100/PT1000) can achieve ±0.05°C to ±0.1°C accuracy with 3-wire or 4-wire connection and proper calibration. Thermocouples achieve ±0.5°C to ±1.0°C depending on type (Type T best, Type N good, Type K moderate) and cold junction compensation accuracy. Thermistors can achieve ±0.1°C to ±0.3°C in their linear range. Key factors affecting accuracy: sensor calibration, lead wire compensation, reference resistor tolerance (use 0.1% or better), PCB thermal gradients, and EMI/RFI interference. For highest accuracy, perform system calibration at multiple temperature points and implement digital linearization in firmware.

Use RTDs for best accuracy (±0.1°C); use thermocouples for wide temperature ranges; use thermistors for cost-sensitive applications.

Lead wire compensation depends on RTD wiring configuration: For 2-wire RTDs, lead resistance adds directly to measurement error (approximately 0.4°C per ohm for PT100). Use only for short cable runs (<1m) or compensate in software if cable length is fixed. For 3-wire RTDs, use the AD7124-4's dual excitation currents - IOUT0 excites the RTD while IOUT1 flows through the return lead, canceling lead resistance. This assumes both leads have equal resistance. For 4-wire RTDs (Kelvin connection), sense wires connect to AD7124-4 high-impedance inputs - no current flows in sense leads so no voltage drop occurs. This provides best accuracy and is recommended for laboratory-grade measurements. For thermocouples, use thermally conductive connection blocks to minimize temperature gradients at the cold junction.

Use 4-wire for best accuracy; use 3-wire with dual excitation for good accuracy with fewer wires; avoid 2-wire for precision applications.

The AD7124-4 offers excellent power efficiency for battery applications: In full power mode with 10SPS data rate, average consumption is approximately 200μA including MCU wake time. In low power mode, this drops to 25μA average. For a typical temperature sensor reading every second: wake from standby (10μs at 255μA), perform conversion (100ms at 255μA), transmit data (50ms at 15mA for wireless), then return to standby (9.5μA). Average consumption is approximately 15-20μA, enabling 5+ year operation on a CR2032 coin cell. For multi-year battery life: use low power mode, minimize conversion time, batch readings and transmit in bursts, and use the AD7124-4's standby mode between conversions.

Use low power mode with 10SPS for battery applications; average 15-20μA enables 5+ year coin cell operation.

The AD7124-4 includes comprehensive diagnostic features for sensor fault detection: 1) Burnout detection - excitation currents detect open sensor wires (overrange reading)

2) Short detection - measures near-zero voltage for shorted sensors

3) Reference monitor - detects reference voltage faults

4) Power supply monitor - tracks AVDD and IOVDD levels

5) Conversion check - verifies ADC conversion integrity. Implement a diagnostic routine that runs periodically: set excitation current to 500μA and check if reading is within valid range

if overrange, sensor or wiring is open

if underrange, sensor may be shorted. For critical applications, implement redundant sensors and cross-check readings. The AD7124-4's status register provides real-time fault indicators that can trigger alarms or switch to backup sensors.

Enable burnout detection for open wire detection; implement periodic diagnostic scans; use redundant sensors for critical applications.

Yes, the AD7124-4 supports mixed sensor types on different channels. Each of the 4 differential channels can be configured independently with different PGA gains, excitation currents, and conversion settings. For example: Channel 0 - PT100 RTD with 500μA excitation, gain 16

Channel 1 - Type K thermocouple with gain 128

Channel 2 - NTC thermistor with voltage divider

Channel 3 - 4-20mA current loop. The AD7124-4's flexible input multiplexer allows switching between channels with different configurations. Firmware must track each channel's sensor type and apply appropriate scaling and linearization. For systems requiring more than 4 channels, use external multiplexers (ADG738) or multiple AD7124-4 devices synchronized via SPI.

Configure each channel independently for different sensor types; use external multiplexers to expand beyond 4 channels.