Product Review: RTDs and Thermocouples

This article was originally published on May 2, 2022, and updated on October 29, 2025.

Maintaining accurate temperature measurement in industrial environments can be challenging. Exposure to extreme heat, cold, vibration, or pressure can affect sensor performance and reliability. Resistance temperature detectors (RTDs) and thermocouples are the most common instruments used to deliver stable, repeatable temperature readings in these demanding conditions.

With decades of experience in pressure and temperature measurement, Ashcroft® designs temperature sensors that combine proven accuracy with rugged construction to meet the needs of diverse industries.

In this Product Review, you’ll learn how RTDs and thermocouples operate, explore the features and benefits of Ashcroft’s temperature sensors and compare which model best fits your application.

RTDs (Resistance Temperature Detectors) and thermocouples are both widely used for process temperature measurement, but they differ in operating principle and performance.

• RTDs measure temperature by detecting the change in electrical resistance of a metal—typically platinum—as temperature increases or decreases. They offer high accuracy, excellent repeatability and long-term stability.
  
  
• Thermocouples generate a voltage when two dissimilar metals are joined and exposed to a temperature difference. They are rugged, self-powered and capable of measuring a much wider temperature range than RTDs.

Choosing between an RTD or thermocouple depends on your process conditions. RTDs are ideal for moderate temperatures requiring precision, while thermocouples excel in high-temperature measurement and harsh environments.

Ashcroft® S50 Direct Mount RTD/Thermocouple Probe

The Ashcroft® S50 Industrial RTD and S50 Industrial Thermocouple are versatile temperature probes designed for direct process installation. Available as either an RTD or thermocouple, the S50 offers durable construction, accurate performance and a variety of connection options for industrial applications.

Features and Benefits

• Flexible configuration: Available as RTD (100 or 1,000 ohm, 2-, 3-, or 4-wire) or thermocouple (Types J, K, T, N, E).
• Durable stainless-steel construction: 316L stainless steel sheath or Inconel ensures corrosion resistance and long service life.
• Multiple process connections: Includes NPT fittings with DIN/spring-loaded mount options for installation flexibility.
• Explosion-proof options: Available with FM, ATEX and IECEx approvals for hazardous locations.
• Integrated design: Combines the probe and connection head for compact, robust installations.
• Accurate and stable: RTD accuracy per IEC 60751 Class A or B; thermocouple performance per ASTM E230.

Typical Applications

• General industrial process measurement
• Chemical and petrochemical systems
• Power generation
• OEM equipment 

Figure 1. Ashcroft S50 RTD/Thermocouple Specifications

Ashcroft® S80 Remote Mount Thermocouple Probe

The Ashcroft® S80 Remote Mount Thermocouple is engineered for applications where heat, vibration, or limited space prevent direct probe installation. A flexible extension cable separates the sensing element from the connection head, allowing safe, accessible placement.

Features and Benefits

• Remote-mounted design: Protects electronics from heat and vibration while enabling easier maintenance.
• Wide temperature coverage: Measures from cryogenic levels up to 1700 °C (3100 °F), depending on thermocouple type.
• Rugged construction: 316 stainless steel or optional Inconel® 600 sheath for superior durability.
• Configurable sensing element: Single or dual thermocouple elements (Types J, K, T, N, E).
• Hazardous location options: FM, ATEX and IECEx approvals are available for Intrinsically Safe or Non-Incendive (Class 1, Div. 2) installations.
• Optional flex armor cable: Adds mechanical protection and strain relief for demanding field conditions.

Typical Applications

• General industrial process measurement
• Chemical and petrochemical systems
• Power generation
• OEM equipment 
• Furnaces and high-temperature process monitoring

Figure 2. Ashcroft S80 Thermocouple Probe Specifications

Ashcroft® S81 RTD Probe

The Ashcroft S81 Remote Mount RTD is designed for high-accuracy temperature measurement when the probe must be isolated from harsh conditions. Its remote head configuration allows flexible mounting and measurement stability.

Features and Benefits

• Precision sensing: Platinum RTD element (100 or 1,000 ohm) with 2-, 3-, or 4-wire configurations for optimal accuracy.
• Remote-mounted head: Keeps the transmitter away from heat and vibration for longer service life.
• Versatile sheath sizes: Available in 1/8", 3/16" and 1/4" diameters for process adaptability.
• Dual-element option: Provides redundancy.
• Hazardous location options: FM, ATEX and IECEx approvals are available for Intrinsically Safe or Non-Incendive (Class 1, Div. 2) installations.
• Flexible lead protection: Optional flex armor for mechanical durability and routing protection.

Typical Applications

• General industrial process measurement
• Chemical and petrochemical systems
• Power generation
• OEM equipment 
• Pharmaceutical, food and beverage processing
• Cryogenic or precision-controlled environments

Figure 3. Ashcroft S81 RTD Probe Specifications

Choosing the Right Temperature Sensor

Each Ashcroft temperature sensor is designed to meet specific needs:

• Choose the S50 when a direct process mount is required.
• Select the S80 for harsh environments requiring remotely mounted probes.
• Opt for the S81 when precision, stability and remote installation flexibility are key.

Ready to learn more?

With a better understanding of how Ashcroft’s RTDs and thermocouples provide proven reliability to keep your process running safely and efficiently, you can now select which option is right for you. We also have additional articles that can provide more information about temperature sensors and more:

• Fitting a Thermowell to Bimetal Thermometers or RTDs/Thermocouples
• What is a Thermocouple?
• What is an RTD?
• How Much Do Temperature Sensors Cost?
• Why Fully-Certified RTDs and Thermocouples are Critical for Hazardous Locations 

Contact us to speak to a temperature specialist and get all of your temperature measurement questions answered. In the meantime, download our guide to learn more about our RTD and Thermocouple probe options: