An RTD to digital converter measures the resistance of a platinum RTD and provides a digital value for a controller or processor. It is a signal-conditioning component in the measurement chain; it is not the RTD probe itself. For system design, select the converter and probe together, then account for lead wiring, reference components, installation, and the required error budget.
How RTD conversion works
The converter excites or measures the RTD in relation to a reference and digitizes the resulting resistance ratio. Firmware then applies the correct RTD resistance-temperature relationship and checks for wiring faults where supported. Interface, wiring modes, supported RTD type, conversion behavior, and fault handling vary by converter. For example, the Analog Devices MAX31865 data sheet documents one SPI RTD-to-digital converter; use the selected component’s current data sheet for its design limits.
Match the RTD and converter
Confirm whether the application uses a Pt100, Pt1000, or another supported element; then check the converter’s resistance range, reference resistor requirements, excitation, input protection, interface, and firmware or driver support. Choose the 2-, 3-, or 4-wire arrangement based on the converter design, cable length, wiring environment, and error budget. A wiring mode is only useful when the sensor, converter, harness, and configuration all support it.
Account for probe installation
The converter cannot correct a poorly coupled or incorrectly installed probe. Specify the sensing location, immersion or surface contact, sheath and dimensions, cable and connector, strain relief, and exposure to moisture, vibration, or chemicals. Evaluate self-heating, electrical noise, grounding, and thermal lag in the completed assembly, not only on the development board.
RTD digital interface design checklist
- RTD nominal type, tolerance class, and required temperature span.
- Converter model, reference components, excitation, supply, and digital interface.
- Lead configuration, cable length, connector, grounding, and shielding approach.
- Installed accuracy target, calibration/verification plan, fault response, and sample rate.
- Probe drawing, mounting conditions, environmental exposure, and production inspection.
Source a compatible RTD probe
Review Starlight’s RTD temperature sensor range when selecting a remote probe for a digital converter. The converter board and RTD assembly are distinct items, so confirm exactly which components are needed for your project. For a custom probe, share the converter input, cable, mounting, and environmental requirements for an OEM review.
