By Brian Smith
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29 May, 2021
RTD assemblies can come in many shapes, sizes, and configurations, and so you should take special care when choosing a RTD assembly for specific applications. Learning about RTD assemblies makes it easier to choose wisely. What is the difference between 2, 3, and 4 wire configurations? PT 100 RTDs contain sensing elements introducing additional resistance to a circuit (through connectors, lead wires, and measuring instruments). As a result, you must remove unwanted resistance during the measuring of voltage drops across the sensing element. The configuration of a circuit determines the accuracy of resistance being calculated and the amount of distortion created from resistance within the circuitry. A sensor's lead wire, used between the measuring instrument and the resistance element, offers resistance that also needs to be acknowledged. Two-Wire Configuration – this type of configuration is considered the simplest RTD circuit design. A single lead wire connects the ends of the RTD element with the monitoring device. When calculating resistance, readings include the resistance coming from lead wires and connectors. Three-Wire Configurations – these are the most used configurations for RTD circuit design. It is seen as an industrial process for monitoring applications. Two wires link a sensing element to a monitoring device. Four-Wire Configuration – this is the most complex of configurations. In this design, two wires link a sensing element to monitoring devices (both sides of the element). One set of wires is used to deliver currents needed for measurements. The other set of wires is responsible for measuring voltage drops over the resistor. Related Reading The Main Reason to Use NTC Thermistors What is Sensor Drift and Self-Heating NTC and PTC Thermistors