What power supply does the RTDT Series RTD transmitter require?

The RTDT Series transmitters are loop powered and operate from a supply voltage of 13 to 40 VDC, with a typical loop supply of 24 VDC. The minimum supply voltage required depends on the total loop resistance — a loop resistance graph is provided in the product documentation to help determine the correct supply voltage for a given installation. The transmitter also includes reversed polarity protection to guard against incorrect wiring connections.

Are the TC, RTD, and RTDT assemblies suitable for outdoor and harsh industrial environments?

Yes. The 304 stainless steel thermowell is rated for up to 7000 psi (48.2 MPa) at 70°F, providing protection to the spring-loaded sensing element against process pressure and mechanical damage. The cast aluminum connecting head meets NEMA 4 requirements, offering protection against rain, splashing water, and windblown dust — making it suitable for outdoor installations on engines, compressors, and process piping. The connecting head maximum operating temperature is 400°F (204°C).

TC RTD and RTDT Series thermocouple RTD temperature sensor assemblies with 304 stainless steel thermowell and NEMA 4 cast aluminum connecting head for industrial process temperature measurement

TC · RTD · RTDT Series

Type J & K Thermocouple | 100Ω Pt RTD | 4-20 mA Transmitter

Temperature Sensing · Thermowell Assemblies · Industrial Process Measurement

TC, RTD & RTDT Series – Thermocouple, RTD and RTD Transmitter Assemblies with Thermowell

The TC, RTD, and RTDT Series are complete, ready-to-install temperature sensor assemblies that combine a rugged 304 stainless steel thermowell with a spring-loaded sensing element and a NEMA 4 cast aluminum connecting head. The TC Series covers Type J and Type K thermocouple configurations, the RTD Series provides high-accuracy 100-ohm platinum resistance sensing, and the RTDT Series delivers a fully loop-powered 4-20 mA DC output for direct integration with PLCs, controllers, and DCS systems. With three thermowell insertion lengths available, these assemblies serve a wide range of industrial temperature measurement needs across engine, compressor, pump, and process applications.

1800°F Type K Max Temp

4-20mA RTDT Output

±0.1% Transmitter Accuracy

NEMA 4 Head Protection

Key Features

The TC, RTD, and RTDT Series temperature assemblies are engineered for reliable, long-service-life temperature measurement in demanding industrial environments. Each assembly arrives as a complete unit — thermowell, sensing element, and connecting head — eliminating the need to source and assemble components separately. Whether the application calls for the wide temperature range of a Type K thermocouple, the precision of a platinum RTD, or the convenience of a 4-20 mA loop signal from the RTDT transmitter, these assemblies deliver accurate and stable readings inside a protected, field-ready package. The spring-loaded element design ensures consistent contact within the thermowell across varying process pressures and flow conditions, while the cast aluminum NEMA 4 head shields the terminal connections from the weather and industrial wash-down environments commonly encountered in oil and gas, power generation, and marine applications.

304 Stainless Steel Thermowell with High-Pressure Rating: The thermowell is manufactured from 304 stainless steel and rated for up to 7000 psi (48.2 MPa / 482 bar) at 70°F (21°C). It provides a sealed pressure boundary between the process medium and the sensing element, allowing the element to be inspected or replaced without shutting down or draining the process. This design is essential for applications involving pressurized pipelines, heat exchangers, and process vessels where direct-immersion sensors are not practical.
Spring-Loaded Sensing Element for Consistent Contact: All sensing elements — thermocouple and RTD — are spring-loaded within their respective stainless steel sheaths. This spring tension maintains firm element-to-thermowell contact regardless of changes in process pressure, vibration, or thermal expansion and contraction, ensuring that the sensing element remains in thermal equilibrium with the thermowell at all times. The result is stable, repeatable readings without the drift that can occur with loosely seated elements.
Type J and Type K Thermocouple Assemblies for Wide Temperature Coverage: The TC Series offers Type J ungrounded thermocouple assemblies rated up to 900°F (482°C) and Type K assemblies rated up to 1800°F (982°C). Both types use a magnesium oxide (MgO) insulated element at 96% purity within a 304 stainless steel sheath, and both are ungrounded for electrical isolation from the thermowell — important for noise-free signal transmission in environments with ground loops or high electrical interference. Combined accuracy for J and K types is 0.5%.
100-Ohm Platinum RTD with 3-Wire Lead Configuration: The RTD Series uses a 100-ohm platinum resistance element at 0°C with a temperature coefficient of 0.00385 (IEC 60751 Class B), housed in a spring-loaded 316L stainless steel element sheath for superior corrosion resistance. The 3-wire lead configuration compensates for lead resistance, allowing accurate readings even over longer cable runs without the errors introduced by the 2-wire method. RTD accuracy is ±0.12%, significantly better than thermocouple accuracy, making the RTD the preferred choice where tight measurement tolerances are required.
Loop-Powered 4-20 mA RTD Transmitter with Reversed Polarity Protection: The RTDT Series incorporates a loop-powered transmitter that converts the platinum RTD resistance reading into a linearized 4-20 mA DC output signal. Operating from a supply voltage of 13 to 40 VDC (typically 24 VDC), the transmitter draws its power from the same two-wire loop that carries the signal — eliminating the need for a separate power connection. Linearized output means the current signal changes proportionally with temperature across the full measurement range, simplifying scaling at the receiving instrument. Reversed polarity protection guards against wiring errors during commissioning and maintenance. Transmitter accuracy is ±0.1%.
Cast Aluminum NEMA 4 Connecting Head with Ceramic Terminal Block: The connecting head is die-cast aluminum and meets NEMA 4 requirements for protection against rain, splashing water, and windblown debris — suitable for outdoor process installations and wash-down environments. Inside the head, a ceramic Steatite terminal block (NEC Class 2 rated) provides 4 terminals for thermocouple connections or 6 terminals for 3-wire RTD connections, accommodating wire sizes from 28 to 14 AWG secured with 8-32 stainless steel screws. The head is rated for continuous operation up to 400°F (204°C) ambient at the connection point.
Three Thermowell Insertion Lengths for Versatile Pipe and Vessel Compatibility: Complete assemblies are available with thermowell insertion lengths of 2-1/2 in. (63 mm), 4-1/2 in. (114 mm), and 7-1/2 in. (191 mm), and with 1/2 NPT or 3/4 NPT process thread connections. This selection covers a broad range of pipe schedules and vessel wall thicknesses, allowing the sensing element to be correctly positioned at the thermal center of the flow stream for maximum measurement accuracy.

Applications

Industrial Engine and Compressor Temperature Monitoring: Gas engines, diesel engines, and reciprocating compressors require continuous temperature monitoring of cylinder heads, exhaust ports, jacket water, and intercooler outlets. The TC Series thermocouple assemblies — particularly Type K for high-temperature exhaust points — and the RTD Series for coolant and lube oil circuits provide accurate, reliable readings that feed alarm and shutdown systems, protecting expensive rotating equipment from overtemperature damage.
Oil and Gas Process Piping and Pressure Vessels: Upstream and midstream oil and gas facilities routinely monitor temperatures on separator vessels, heat exchangers, pipeline segments, and gas processing columns. The high-pressure-rated 304 SS thermowell allows safe installation in pressurized systems, and the NEMA 4 head protects terminal connections in outdoor and classified-area environments. The RTDT Series 4-20 mA output integrates directly into safety instrumented systems and SCADA platforms without additional signal conditioning.
Marine Engine Rooms and Offshore Platform Systems: Marine propulsion engines, generator sets, and auxiliary machinery on ships and offshore platforms demand rugged, corrosion-resistant temperature sensing that can withstand vibration, salt atmosphere, and wash-down cleaning. The stainless steel thermowell and NEMA 4 connecting head address these requirements directly, while the spring-loaded element design maintains measurement integrity under the continuous vibration characteristic of shipboard installations.
Pump and Heat Transfer Systems: Pump packages monitoring bearing temperatures, mechanical seal flush temperatures, and process fluid outlet temperatures benefit from the RTD Series' high accuracy and stable long-term performance. Where the process control system requires a standard current loop input — as is common with variable speed drives, PLC analog input cards, and DCS analog input modules — the RTDT Series delivers a plug-and-play signal without requiring a separate head-mount or DIN-rail transmitter.
Power Generation Auxiliary Systems: Cooling water circuits, steam condensate lines, fuel oil handling systems, and turbine lube oil systems in power generation facilities require accurate and dependable temperature measurement across a wide range of process conditions. The complete-assembly format of the TC, RTD, and RTDT Series — with all components pre-matched and tested — simplifies procurement, reduces installation time, and ensures compatibility between the thermowell, element, and transmitter from a single source.
Industrial Process Control and SCADA Integration: In any process environment where temperature data needs to be transmitted to a remote controller, data logger, or SCADA system over standard 4-20 mA wiring — including chemical processing, water treatment, food and beverage, and pharmaceutical manufacturing — the RTDT Series provides a self-contained transmitter solution. The linearized output simplifies programming at the receiving instrument, and the loop-powered design minimizes the wiring infrastructure required in the field.

Technical Specifications

Specifications listed below apply to the TC Series thermocouple assemblies, RTD Series resistance temperature detector assemblies, and RTDT Series RTD transmitter assemblies. All assemblies include thermowell.

Parameter	Specification
Thermowell Material	304 Stainless Steel
Thermowell Pressure Rating	7000 psi (48.2 MPa / 482 bar) max at 70°F (21°C)
Thermowell Insertion Lengths	2-1/2 in. (63 mm) · 4-1/2 in. (114 mm) · 7-1/2 in. (191 mm)
Process Thread Connection	1/2 NPT or 3/4 NPT (model dependent)
Connecting Head Material	Cast Aluminum; NEMA 4; NEC Class 2
Connecting Head Max Operating Temp	400°F (204°C)
Thermocouple Types (TC Series)	Type J and Type K; ungrounded; magnesium oxide (MgO) insulated at 96% purity
Thermocouple Element Sheath	304 Stainless Steel; spring-loaded
Type J Operating Temperature	Up to 900°F (482°C)
Type K Operating Temperature	Up to 1800°F (982°C)
Thermocouple Accuracy (J/K)	0.5%
RTD Element Type (RTD/RTDT Series)	100 ohm Platinum at 0°C; 3-wire leads
RTD Temperature Coefficient	0.00385 per °C (DIN/IEC 60751)
RTD Element Sheath	316L Stainless Steel; spring-loaded
RTD Max Operating Temperature	400°F (204°C)
RTD Accuracy	±0.12%
RTDT Input Compatibility	2-wire or 3-wire 100 ohm Platinum RTD; 0.00385 temp coefficient
RTDT Output Signal	Linearized 4-20 mA DC
RTDT Measurement Ranges	0° to 400°F (-17.8° to 204°C) and -60° to 140°F (-51.1° to 60°C)
RTDT Supply Voltage	13 to 40 VDC (loop powered; typically 24 VDC)
RTDT Transmitter Accuracy	±0.1%
RTDT Polarity Protection	Reversed polarity protection included
Terminal Block Material	Ceramic Steatite; NEC Class 2
Terminal Block — TC Assemblies	4 terminals; 28 to 14 AWG wire; 8-32 SS screws
Terminal Block — RTD Assemblies	6 terminals; 28 to 14 AWG wire; 8-32 SS screws
Optional Extension Wire — Insulation	Individual conductor: extruded PFA; Duplex: twisted, extruded PFA overall
Optional Extension Wire — Temp Rating	Continuous -450° to 500°F (-267° to 260°C)
Optional Extension Wire — Gauge	20 AWG (0.5 mm²); metallic shield; moisture resistance: excellent
Extension Wire Resistance — Type J	0.357 ohms per double foot
Extension Wire Resistance — Type K	0.586 ohms per double foot

Technical FAQ

Common Questions Answered

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The TC Series consists of thermocouple assemblies — available in Type J (up to 900°F / 482°C) or Type K (up to 1800°F / 982°C) — for millivolt-output temperature measurement. The RTD Series uses a 100-ohm platinum resistance element with 3-wire leads for high-accuracy resistance-based temperature sensing up to 400°F (204°C). The RTDT Series builds on the RTD by adding a loop-powered transmitter that converts the RTD reading into a linearized 4-20 mA DC signal, making it directly compatible with PLCs, DCS systems, and controllers that accept standard current-loop inputs without requiring a separate signal conditioner.

Complete assemblies are available in three thermowell insertion lengths: 2-1/2 in. (63 mm), 4-1/2 in. (114 mm), and 7-1/2 in. (191 mm). The correct length is selected based on the pipe diameter and the depth required to position the sensing element in the center of the process flow for accurate and representative temperature readings.

The RTDT Series transmitter is loop powered and operates from 13 to 40 VDC, with a typical loop supply of 24 VDC. The minimum supply voltage required depends on the total loop resistance — a loop resistance graph in the product documentation helps determine the correct supply for a given installation. Reversed polarity protection is included to guard against incorrect wiring connections.

Thermocouple assemblies (Type J and Type K) have an accuracy of 0.5%. RTD assemblies achieve ±0.12% accuracy due to the inherently stable characteristics of the platinum resistance element. The RTDT transmitter adds ±0.1% transmitter accuracy on top of the RTD element measurement, delivering a highly accurate combined current-loop output for process control and monitoring.

Yes. The 304 stainless steel thermowell is rated for up to 7000 psi (48.2 MPa) at 70°F, protecting the spring-loaded element against process pressure and mechanical damage. The cast aluminum connecting head meets NEMA 4 requirements for protection against rain, splashing water, and windblown dust, making these assemblies well suited for outdoor installations on engines, compressors, and process piping. The maximum head operating temperature is 400°F (204°C).

The ceramic Steatite terminal block accepts wire sizes from 28 to 14 AWG, secured with 8-32 stainless steel screws. Thermocouple assemblies have a 4-terminal block, and RTD assemblies have a 6-terminal block to accommodate the 3-wire configuration. Optional Type K thermocouple extension wire in 20 AWG with PFA insulation, metallic shielding, and excellent moisture resistance is available separately for extended wiring runs.