What a Duplex RTD Assembly Contains
A duplex RTD probe houses two sensing elements in one assembly. The elements can support separate measurement channels, comparison or a designated backup function when the application and control system are designed for that purpose. A duplex construction alone does not provide a safety function, guarantee redundancy or establish that both elements have identical characteristics. Confirm the wiring diagram and datasheet for the exact assembly.
Specify Each Element Independently
Define the nominal resistance and reference temperature for each element (for example, Pt100 or Pt1000 only when confirmed by the supplier), its resistance–temperature curve, tolerance class and lead-wire configuration. State whether the two elements must match, have separate ranges, or serve different measurement channels. Do not assume the element pair is matched or that a particular IEC tolerance applies unless it is documented for the ordered part.
IEC 60751:2022 defines requirements and the resistance–temperature relationship for industrial platinum resistance thermometers and sensors. Check the quoted sensor’s actual class, curve and operating limits against the current datasheet.
Match Wiring and Readout to the Controller
Confirm the number of leads for each element, terminal assignment, cable length, connector and controller input. A duplex probe may bring both elements to a common head or connector, but pin assignments are assembly-specific. Verify that the measurement channels support the selected two-, three- or four-wire arrangement and conversion method. NI’s RTD measurement guide explains how wiring configuration affects lead-resistance error.
Specify the process connection and installation as well: sensing point, insertion length, sheath material and diameter, pressure or flow conditions, vibration, moisture, cable routing and connector access. The installed probe’s thermal contact and mounting can affect the reading independently of the element’s nominal curve.
Plan Validation and Channel Use
Decide how the two elements will be used: independent process channels, comparison during commissioning, or a backup input where the controller and operating procedure support it. Define how the system identifies an open circuit, disagreement or failed channel; the sensor assembly by itself does not set alarm behavior. Validate each element through its own wiring and readout at stable points over the required range, and record the reference, test conditions, acceptance limits and calibration approach.
Information for an OEM RFQ
Provide the required resistance and curve for each element, tolerance, wire count and diagram, probe drawing, sheath and process connection, insertion depth, cable and connector, operating environment, controller model, validation requirements, sample quantity and annual volume. Ask the supplier to identify which values are guaranteed for the supplied part and which depend on the completed assembly. Review our RTD sensor range and RTD sensor types guide, or request an OEM quotation with your drawing.
