How Do I Select a Temperature Sensor for Harsh Environment Conditions?

Many mission critical applications demand a temperature measurement solution that can perform well in extremely harsh environments.  Harsh environments can wreak havoc on temperature sensors and warrant special attention during sensor design and development.

In harsh environments, temperatures are typically measured using a thermocouple or a resistance temperature detector (RTD) inside a thermowell or protection tube that is connected to a control system with an electronic transmitter. If a temperature sensor system is not designed or manufactured properly for a harsh environment, the sensor system may not perform well, or even worse, fail during service.

When selecting a temperature sensor system for harsh environments, an engineer must determine whether to develop a custom sensor system or purchase one off-the-shelf.  In demanding applications, custom designs are often the most cost effective way to deliver the required performance, robustness and size-weight-and-power (SWAP).

Harsh Environments Affect Sensor System Designs

Temperature sensor systems used in mission critical applications face a wide variety of thermal, mechanical, electrical, and chemical environmental stresses.  Over their service lives these environmental stresses age sensor systems and can induce system failure through a number of failure modes:

  • wear
  • cracking
  • fracturing
  • deformation
  • corrosion
  • fatigue

Industrial applications often include harsh environmental operating conditions that accelerate failure modes.  These conditions include:

  • dynamic thermal pressure cycling
  • radiation
  • vibration
  • humidity
  • corrosion
  • mechanical shock
  • thermal shock

Environmental stresses age a sensor system and cause mechanical joints and welds to weaken, electrical components to degrade, and the performance of the sensor to drift.  In combination with the behavior of various specialized materials in temperature sensor systems, environmental factors add complexity to finding the optimal temperature sensor solution for critical applications.

An ideal temperature sensor system optimizes performance parameters such as response time, accuracy, and reliability.  Target performance is achieved through proper analysis and selection of components including the sheath, internal and external leads, sensing element, potting materials, electrical connections, and protection systems.

Materials Matter

Selecting components with the correct heat transfer, strength, and electrical properties is vital to achieving the ideal sensor system design.  Each component must perform individually and in combination with one another to optimize sensor performance and longevity.  Essential material properties include thermal diffusivity, thermal resistance and shock, fatigue resistance, and cost.  They can all vary significantly with environmental extremes, so care must be taken to analyze the components’ properties versus the target operating conditions.  The material properties and geometry of each component are then modeled and tested to arrive at the ideal design.

Every Application is Unique

Within and across industries, every sensor application is truly unique. Slight variations in application parameters create entirely new challenges. Experience plays a key role in defining the requirements, creating designs, simulation, selecting materials, and testing.  In regulated applications, it is extremely important to understand the implications of qualification testing and similarity analysis to other qualified designs.  Ultimately, every sensor must be designed and built to meet the unique requirements of its mission critical application.

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Experience Matters but Innovation Is Paramount

RTDs and thermocouples have been designed and manufactured successfully for decades, but materials, tooling, and processes are constantly evolving. Each new application presents a new set of challenges that can be overcome through innovation and experience.

Ultra Electronics has been at the forefront of harsh environment temperature sensor system development for over 40 years.  We can help you define the requirements for your application, select the correct materials and build the optimal temperature sensor system that provides the necessary performance and survivability for your critical application.

Ultra Electronics delivers the Weed Instrument brand of temperature sensors and the critical application expertise based on decades of industry experience that comes with it.  Engineers choose Ultra Electronics when they want to maximize the performance envelope and service life of a given component through quality, custom design, engineering, and manufacturing.

Further reading

Accelerated Aging of Materials and Structures: The Effects of Long-Term Elevated-Temperature Exposure (1996),

Effect of Temperature on Mechanical Response of Austenitic Materials