Know more about RTD Sensors

What are RTD Sensors?

Resistance Temperature Detectors (RTDs) are highly reliable, high accuracy sensors used for precise temperature measurement. Commonly known as RTD probes or temperature probes or Platinum Resistance Thermometers (PRTs), these devices are typically made with platinum elements and operate by sensing changes in electrical resistance as temperature varies.

There are different types of RTD sensors available, along with multiple wiring configurations such as 2-wire, 3-wire, and 4-wire, each suited to specific application requirements.

How does the RTD Sensor Probe work?

RTD sensors are devices whose working principle is based on the variation in the electrical resistance of metals with temperature. As the temperature increases, the resistance of the metal conducting element in the RTD increases. This measurable change is then converted into an accurate temperature reading.

This is achieved by passing a constant current through the RTD element resistance, converting it into a voltage. This is accomplished in devices such as two-wire temperature transmitters, which measure the non-linear resistance of the RTD element and linearise the measurement, to give a temperature linear output.

The temperature vs. resistance relationship as well as tolerances conform to the standard IEC 60751:2022 (or the German standard DIN EN IEC 60751:2023-06). Both these standards are based on the ITS-90 temperature scale.

Platinum RTDs, largely Pt100 sensors, are widely used for precise temperature measurement. These sensors are defined by a base resistance (R₀) of 100 Ω at 0°C.

They offer a broad operating range from –200°C to 850°C, over which their resistance vs temperature characteristic is defined. In practice, typical industrial usage is up to 400°C.

The sensitivity of the RTD is represented by the temperature coefficient (α), derived between 0°C and 100°C:

ɑ = (R100 - R0) / (R0 x ΔT)

While pure platinum exhibits a coefficient of 0.003926, standardized RTDs conform to 0.00385 as per IEC 60751 and ASTM E1137 standards. This is achieved through controlled material modification to ensure consistency and repeatability.

Types of RTD Sensors

RTDs are available in different types based on sensing element, construction, and application requirements. Selecting the right type of RTD depends on accuracy needs, installation conditions, and process environment.

Based on Sensing Element

1. Pt100 RTD: The most commonly used RTD, with a resistance of 100 Ω at 0°C. It offers high accuracy, stability, and is suitable for a wide range of industrial applications.
2. Pt1000 RTD: With a resistance of 1000 Ω at 0°C, this type provides higher sensitivity and better performance over longer cable distances.

Based on Construction Type

1. Mineral Insulated (MI) RTD: Built with compacted MgO insulation and a stainless steel sheath (typically SS316), these RTDs are flexible, durable, and ideal for harsh industrial environments.
2. Surface RTD: Used for measuring surface temperature of pipes, vessels, and rotating equipment where insertion is not possible.
3. Hygienic / Sanitary RTD: Designed for pharma, food, and beverage industries, ensuring cleanability and compliance with hygienic standards.
4. Multipoint RTD: Used to measure temperature at multiple locations within a single assembly, ideal for reactors, tanks, and large vessels.

RTD Wiring Configurations

RTD sensors are available in different wiring configurations, which affect measurement accuracy and compensation of lead wire resistance.

1. 2-Wire RTD: The simplest configuration, where the same wires are used for both current supply and measurement. Suitable for short distances where lead resistance has minimal impact.
2. 3-Wire RTD: The most widely used configuration in industrial applications. It compensates for lead wire resistance, offering a good balance between accuracy and cost.
3. 4-Wire RTD: Provides the highest accuracy by completely eliminating the effect of lead wire resistance. Ideal for precision-critical applications and laboratory use.

Common RTD Applications and How Radix Delivers Reliable Solutions

Radix range of RTD Sensors

Radix has built a strong reputation in India for its high-quality, precision-engineered RTD sensors. With over 39 years of manufacturing experience, Radix delivers reliable and well-engineered temperature measurement solutions across industries.

Our RTD sensors are designed and manufactured in compliance with international standards such as ATEX, IECEx, CCOE/PESO, and CE, and can also be supplied with NABL certification for assured quality and traceability.

Terminations & Mounting Options

The Radix range of RTDs is available with multiple termination options, including terminal head (thermocouple head), cable termination, and connectors. These sensors can also be supplied with thermowells and head-mounted temperature transmitters, enabling direct signal output (2-wire, 4-20 mA).

Hazardous Area Compatibility

1. Radix RTD sensors are suitable for both safe and hazardous areas. For hazardous environments, sensors can be supplied with certifications for Zones IIA, IIB, and IIC.
2. They are available with protection such as Ex db gas group IIC (~NEMA 6), T6 PESO, and Ex tb IIIC T85°C Db IP67 (-20°C < Ta < 60°C), ensuring safe operation in demanding conditions.

Wiring Configurations & Sensing Elements

1. Radix RTD sensors are available in 2-wire, 3-wire, and 4-wire configurations to suit varying accuracy and installation requirements.
2. They are offered with both Pt100 and Pt1000 sensing elements, ensuring high accuracy, stability, and compatibility across diverse industrial applications.

Construction & Material

1. Radix provides flexible Mineral Insulated (MI) cables with compacted MgO insulation and SS316 sheath, designed for durability in harsh environments. These are available in multiple outer diameters, including 2.3, 3, 4, 5, 6, and 8 mm.
2. For specific project requirements, RTDs can also be manufactured in US customary units (inches, feet, etc.).

Standards & Accuracy

Manufactured in accordance with IEC 60751 and ASTM E1137 standards, Radix RTD sensors offer high precision with accuracy classes such as:

1. Class A: ±(0.15 + 0.002 × t) °C
2. Class AA: ±⅓ × (0.3 + 0.005 × t) °C

For ultra-high precision applications, Radix also offers ⅕ DIN RTDs.

Terminal Heads and Ingress Protection

Radix terminal heads are available in die-cast aluminium, stainless steel, and polypropylene. These are designed with ingress protection ratings from IP65 to IP68, ensuring reliable performance in harsh industrial environments.

Ingress Protection (IP) ratings define the level of protection against dust and water:

1. IP65: Completely protected against dust and resistant to low-pressure water jets from any direction
2. IP66: Dust-tight and protected against strong water jets
3. IP67: Dust-tight and protected against temporary immersion in water
4. IP68: Dust-tight and suitable for continuous immersion under specified conditions

Temperature Range

Radix RTD sensors are designed for reliable operation in industrial applications up to 400°C.

For specialized applications, sensors can be manufactured to operate at temperatures as low as -200°C and as high as 600°C.

Customization and Build Flexibility

1. Radix manufactures RTDs with customizable lengths ranging from 200 mm to 20,000 mm (8” to 66 ft), enabling flexibility across various process requirements.
2. Transition joint RTDs are also available, typically using PTFE cables rated up to 260°C.

Radix offers RTD sensors for a wide range of applications:

1. Autoclave Temperature Monitoring: Models RAC240, RAC241, RAC251
2. Compact Construction & Pipeline Temperature Measurement: Models RCP201, RCP211
3. Hygienic / Sanitary Applications: Models RHS600, RHS602, RHS701
4. HVAC Applications: Model RHV201
5. General Industrial Applications: Models RHW501, RHW201, RTJ201, RCQ200
6. Surface Temperature Measurement: Models RSW201, RST201, RPB201
7. Acid & Alkaline Environments: Model RAA201
8. Rubber & Tyre Industry: Models RTR200, RTR300, RTR400, RWR200
9. Multipoint Temperature Measurement: Model RHM501

Industries we serve:

With high repeatability, accuracy, and reliability, Radix RTD sensors are widely used across:

1. Process industries
2. Pharmaceutical industry
3. Food and beverage industry
4. Distilleries and dairy
5. Power plants
6. Wastewater treatment
7. Engineering and machinery
8. Steel and metal industry
9. Rubber and tyre industry
10. HVAC systems
11. Battery manufacturing

Our manufacturing facility:

This full range of RTD Sensors is manufactured at our modern, well equipped manufacturing facility in Navi Mumbai. The factory is certified for ISO 9001:2015, ISO 45001:2018 and ISO 14001:2015. These RTD Sensors can also be supplied with a test certificate from our in-house accredited NABL Test Laboratory (NABL - National Accreditation Board for Testing and Calibration Laboratories).

We have a large list of OEM customers from every industry, using customized RTDs designed and developed specially for them. Many OEMs have been using Radix RTDs for over 2 decades.