An RTD to 4–20 mA converter is used when a temperature control or monitoring system requires a current-loop signal from a resistance temperature detector. The RTD senses temperature through a resistance change; a compatible transmitter or signal-conditioning device reads that input and scales it to the configured output. The sensor, converter and receiving equipment must be specified as one measurement chain.
What the converter does
An RTD is a passive resistance-based sensing element. It does not generate a 4–20 mA signal by itself. A transmitter measures the RTD input, applies the selected sensor curve and measurement range, and generates a corresponding current output for a compatible receiver. Product terminology varies, so check the device data sheet to confirm whether it accepts an RTD directly, which wiring options it supports and what output it provides.
For example, WIKA documents its T15 as a resistance-sensor temperature transmitter with a 4–20 mA output and Pt100 configuration options. This is an example of one manufacturer’s model; its specifications do not apply to every RTD transmitter. See WIKA T15 manufacturer information.
RTD input and current output are separate specifications
Confirm the converter input first. Check the supported RTD type, nominal resistance, wiring arrangement and configurable measurement range against the sensor data. A Pt100 and a Pt1000 are not interchangeable input selections unless the device documentation explicitly supports both. NTC thermistors also have different resistance-temperature characteristics and require a compatible input profile; an RTD input must not be assumed to accept an NTC probe.
Then confirm the output side: the receiving device must accept a current-loop signal, use the same measurement scaling, and meet the transmitter’s documented supply and load requirements. Review isolation, diagnostics and fault-output behavior if the application requires them. Do not rely on broad claims about noise immunity, distance or accuracy without checking the chosen device, cable and system design.
Selection checklist for an OEM project
- Sensor: RTD type, nominal resistance, wiring and available sensor data sheet.
- Measurement range: intended process range and transmitter configuration limits.
- Output: 4–20 mA requirement, receiver input and matching scale endpoints.
- Electrical conditions: supply, loop load, cable routing, grounding and environmental noise as specified by the device maker.
- Installation: probe dimensions, mounting, process contact, cable length and transmitter location.
- Validation: verify the assembled sensor, transmitter and controller together across representative operating points; document scaling and fault behavior.
For a Pt100-specific discussion, see our Pt100 and 4–20 mA RTD transmitter selection guide. You can also compare RTD and thermocouple sensor options or review our RTD temperature sensor range.
Information to share when requesting a quote
Provide the application and process medium, required temperature range, RTD type and wiring, probe and mounting dimensions, cable requirements, converter location, receiving instrument input, supply conditions, target output scaling and any drawing or sample. These details help the engineering team assess the sensor and signal interface together.
Contact Starlight Sensors to discuss an OEM temperature-sensing project or request a quote.
