Resistance Temperature Detectors (RTDs) are commonly used temperature sensing devices in many industrial processes where accuracy, stability, and repeatability are critical. Unlike purely mechanical devices, RTDs provide a resistance signal that can be brought into modern PLC, DCS, or SCADA systems for precise monitoring and control.

In applications such as water and wastewater treatment, chemical processing, food and beverage, utilities, OEM equipment, and general process industries, measuring and maintaining proper temperature in pumps, bearings, gearboxes, tanks, and process lines supports equipment life, uptime, and overall process performance.

How RTDs Work

An RTD is built around a resistive sensing element - typically a platinum PT100 or PT1000 - whose electrical resistance changes in a predictable way with temperature. A PT100 RTD is calibrated to produce 100 ohms of resistance at the freezing point of water (0 °C / 32 °F), while a PT1000 produces 1,000 ohms at that same reference point.

As temperature decreases, the RTD’s resistance decreases; as temperature increases, its resistance increases.

Raw RTD Signal vs. Amplified Output

RTDs are commonly used in two ways: sending the raw resistance into the control system via input modules (PLC, HMI. Loop Controllers, ETC). Or converting the resistance signal within a field transmitter from RTD to a usable signal (Milliamp or Voltage output signals)

• Raw RTD (ohm) signal: Some plants run a direct PT100/PT1000 resistance signal into a PLC or HMI input module that is designed to read ohms and convert that into temperature internally. This approach is more common when the RTD is relatively close to the control panel and the user already has RTD-capable input cards or input modules.
• Amplified RTD signal: Many applications benefit from converting the RTD’s resistance to a robust 4–20 mA or voltage output in a temperature transmitter and then sending that signal back to the PLC over longer distances. A 4–20 mA loop is far less susceptible to line losses and added resistance than a raw RTD signal run over longer distances.

For example, NOSHOK 910/915 Series industrial RTD assemblies can be provided as raw RTD probes or combined with an in-head transmitter to provide a 4–20 mA output from inside the connection head. NOSHOK 800 Series platinum resistance temperature transmitters and 920 Series RTD Transmitters support compact, transmitter-based temperature measurement for industrial control systems.

When to Choose PT100 vs. PT1000

Both PT100 and PT1000 elements are used widely, and choosing one over the other is largely a matter of system design and compatibility - not a simple “one is always more accurate” rule.

• PT100 (100 Ω at 0 °C): Common, well-understood, and widely supported by transmitters and PLC input modules; used in many industrial RTD assemblies and temperature transmitters.
• PT1000 (1,000 Ω at 0 °C): Provides a higher resistance change per degree, which can give better resolution in some systems or match PLC input modules designed specifically for 1,000 Ω sensors.

NOSHOK’s 810 Series Compact OEM Temperature Transmitters use a PT1000 platinum resistance sensor for applications requiring a compact, stable electronic temperature solution.

Local vs. Remote Temperature Indication

There is also an important difference between local indication and remote temperature measurement in practical plant installations.

• Local indication: A local display (example: Bimetal Thermometer or Electronic Indicating Temperature Transmitter/Switch) at the measurement point is used when operators need to see temperature right at the equipment - such as on a pump skid, line, tank, or heat exchanger - without walking back to a control room.
• Remote measurement: RTD-based transmitters typically send temperature back as a 4–20 mA or voltage signal for control, alarming, and trending in a PLC, DCS, or SCADA system.

This is why RTDs and RTD-based transmitters are so often paired with control logic geared toward condition-based maintenance, process monitoring, and trend analysis rather than simple spot checking.

RTDs on Pumps, Bearings, and Gearboxes

A key practical advantage of RTDs is the value they bring when temperature measurement is added to pumps - not just in process lines, but on bearings, housings, and gearboxes - to support maintenance and uptime. In municipal and industrial pumping applications, RTDs can be used with transmitters on pump bearings and oil sumps to monitor temperature, helping operators catch abnormal conditions before they cause failures.

By monitoring both oil pressure, with PT Series pressure transmitters, and temperature, with NOSHOK industrial RTDs and transmitters, users can extend bearing life, reduce unscheduled maintenance, and support planned shutdowns for pump refurbishments.

Bringing It Together Across Industries

Across industrial environments, many facilities still rely on basic indication or minimal instrumentation, and adding RTD-based temperature monitoring is a practical way to improve equipment reliability and process visibility. Using RTDs and RTD transmitters alongside pressure instrumentation gives operators a more complete picture of equipment health and process conditions, whether the application involves pumps, tanks, utility systems, process skids, or treatment operations.

By pairing NOSHOK RTDs, transmitters and accessories correctly - choosing PT100 vs. PT1000 to match PLC inputs, raw vs. amplified signals based on distance, and thermowells where pressure, corrosive media, or high velocity conditions are present - you can build a robust temperature measurement strategy that aligns with how your plant actually runs.