Temperature Probes

A temperature probe (also referred to as a temperature sensor or temperature probe sensor) is an instrument that measures temperature across various mediums, including air, liquids, and surfaces. The precision and accuracy of temperature probes complements thermometers and other industrial temperature data logging devices, providing a comprehensive assessment of prevailing temperature conditions.

These devices operate based on different physical principles depending on their type, ranging from thermoelectric effects (thermocouples) to changes in electrical resistance (RTDs and thermistors) to the expansion and contraction of materials.

The market today offers an extensive range of temperature probes, each with its own characteristics and suitability for different temperature ranges, environments, and measurement needs. Understanding the underlying principles of operation and calibration are key to finding the right temperature sensor for your desired application.

How to Use Temperature Probes

Proper usage of a temperature probe is essential for obtaining accurate measurements. Keep the following in mind when using your temperature probe:

• Ensure Proper Insertion and Placement: For liquids, ensure the probe is fully submerged in the area of interest, avoiding contact with the container walls or bottom unless surface temperature is the target. For air temperature measurements, position the sensor away from direct sunlight or other radiant heat sources that could skew readings. Surface temperature measurements require good thermal contact between the heat probes and the surface; using thermal paste can sometimes improve this contact and enhance the accuracy of your reading.
• Establish a Secure Connection and Setup: Ensure the temperature probe sensor is correctly connected to the measuring instrument, thermometer, or data logger; incorrect connections can lead to inaccurate readings or even damage to the probe or instrument. Always follow the manufacturer's instructions for proper wiring or connection protocols. Always verify that the instrument is configured for the specific type of temp sensor probe being used (e.g., thermocouple type, RTD type).
• Prevent Contamination: Handle temperature probes with care to avoid physical damage to the sensing element or probe sheath. Contamination from oils, dirt, or other substances can affect the accuracy of the measurements especially for surface and immersion probes. Clean the temperature probe according to the manufacturer’s recommendations before each use, particularly in critical applications.
• Allow Sufficient Time for Stabilisation: It will take some time for the temperature probe to reach the same temperature as the object or environment being tested. Any readings taken during this stabilisation period may be inaccurate. Obtaining a reading before the probe has stabilised can also affect accuracy. The stabilisation time can vary depending on the type of probe, the medium, and the temperature difference; it’s important to follow manufacturer recommendations on stabilisation time during application.
• Establish Documentation and Traceability Processes: Regular calibration against traceable standards ensures the reliability and accuracy of industrial temperature sensors over time. This includes recording the probe's serial number, calibration history, and any specific application notes.

What are the Types of Temperature Probes?

1 - Resistive Temperature Detectors (RTD Temperature Sensor)

An RTD, also known as a resistive temperature detector, is a highly precise temperature probe. These RTD temperature sensors typically utilise Platinum and Nickel finishes, offering excellent stability and accuracy over a wide temperature range. They are available in various resistance ranges, including the common PT100 and PT1000 (Platinum) as well as NI100 and Ni1000 (Nickel) configurations.

While RTDs offer superior accuracy and stability compared to some other types, they tend to be more expensive and can be more susceptible to mechanical shock and vibration. Furthermore, like all sensors, RTD temperature sensors have a tendency to drift over extended periods and require periodic calibration to maintain their accuracy.

2 - Negative Temperature Coefficient (NTC Temperature Sensor) Thermistor

Temperature probes employing NTC thermistors (Negative Temperature Coefficient) are characterised by their rapid and highly accurate response to temperature changes. These temperature sensors typically exhibit a significant decrease in electrical resistance as their temperature increases.

NTC thermistors are often more cost-effective than RTDs but generally offer a smaller operating temperature range. NTC thermistors are commonly potted into customised housings to suit specific application needs or client requirements. For epoxy-encapsulated NTCs, the optimal operating temperature range is typically between -40°C and +125°C. However, glass-encapsulated NTCs can withstand high temperatures up to +250°C, making them suitable for more demanding applications.

3 - Thermocouple Prober

Thermocouples are arguably the most widely used type of temperature probe, primarily due to their simplicity, ruggedness, and rapid response to changes in temperature. A thermocouple consists of two dissimilar metal wires joined at one end, creating a junction. When this junction is heated or cooled, a voltage is produced that is proportional to the temperature difference between the junction and a reference point (cold junction).

While thermocouple probes are known for their wide temperature ranges and fast response times, they are generally less stable over extended periods compared to RTDs. This may necessitate more frequent replacement or calibration.

There are numerous types of thermocouples available on the market, each denoted by a letter (e.g. Type J) reflecting the specific metal alloys that dictate their temperature measurement ranges and suitability for different environments:

• Type J (Iron-Constantan): Offers a range of -40°C to +1200°C with high sensitivity (50 μV/°C), suitable for general-purpose applications.
• Type K (Chromel-Alumel): Most common thermocouple type with a broad range of -200°C to +1350°C, widely used in various industrial applications.
• Type T (Copper-Constantan): Ideal for low-temperature measurements, ranging from -200°C to +350°C.
• Type E (Chromel-Constantan): Non-magnetic, offers a higher output voltage (68 μV/°C) and a wide range of -270°C to +740°C.
• Type N (Nicrosil-Nisil): Offers better stability and oxidation resistance with a range of −270°C to +1300°C.

Platinum/rhodium-alloy thermocouples like Types R, S, and B are amongst the most stable options but have lower sensitivity.

• Type R (Platinum/Rhodium-Platinum): Suitable for high-heat measurements, ranging from 0°C to +1600°C. Vulnerable to metallic and non-metallic vapours above 1100°C.
• Type S (Platinum/Rhodium-Platinum): Similar to Type R but with slightly different alloy composition and range up to +1600°C.
• Type B (Platinum/Rhodium-Platinum/Rhodium): Designed for very high-temperature measurements up to +1800°C with limited use below +50°C.

The choice of thermocouple type depends on the specific temperature range and environmental conditions of the application.

How to Avoid Common Mistakes when Purchasing Commercial & Industrial Temperature Probes

Selecting the appropriate temperature probe is crucial for ensuring accurate, reliable, and safe temperature monitoring. Avoid these common mistakes when making your purchase:

• Selecting an Insufficient Temperature Range: Carefully assess the full spectrum of temperatures your process or application might encounter. Select probes with operating ranges that exceed your normal process requirements by at least 25%. This safety margin accounts for unexpected temperature excursions, preventing probe damage and ensuring reliable readings even under abnormal conditions. Additionally, operating a probe consistently near its maximum limit can shorten its lifespan.
• Neglecting Calibration Requirements: Recognise that all temperature probes, regardless of their initial accuracy, will drift over time. Consider the ongoing calibration needs and the availability of suitable calibration services when selecting probes. Some advanced models, particularly high-precision RTDs and specialised thermocouples, may require specialised calibration equipment or procedures. Factor in the cost and downtime associated with regular calibration to ensure long-term accuracy and compliance with any relevant standards or regulations.
• Improper Material Selection: The materials used in the construction of the temperature probe, including the sheath and sensing element, must be compatible with the environment in which they will be used. Using probes with inappropriate materials for your application environment can lead to various issues including chemical contamination of the process, corrosion of the probe sheath due to exposure to harsh substances, or premature failure of the sensor due to material degradation at extreme temperatures or in corrosive atmospheres. For example, Type K thermocouples begin to degrade in a mostly reducing atmosphere due to hydrogen exposure, while Type N does not face the same issues in low-oxygen environments.

Applications of Temperature Probes

Temperature probes are renowned for their robust design and versatility, making them indispensable tools across a multitude of general-purpose industrial, commercial, and scientific applications.

Accurate temperature measurement and monitoring are paramount in these sectors to conduct investigations, ensure equipment functions properly and efficiently, maintain product quality, assist research and development, and ensure safety. These sensor probes are frequently employed in the following areas:

• Air Conditioning and Refrigeration: For monitoring and controlling temperatures in HVAC systems in buildings, industrial facilities, and transportation, ensuring efficient operation and comfortable environments.
• Chemical Industry: For precise temperature control in chemical reactions, storage tanks, and pipelines, ensuring product quality and safety in chemical processing plants.
• Plastics Processing: For monitoring and controlling melt temperatures in injection molding, extrusion, and other plastics manufacturing processes, ensuring optimal product quality and efficient production.
• Stoves and Grills: Meat and food temperature probes are essential for ensuring food safety and quality in commercial kitchens and food processing facilities, by accurately measuring internal cooking temperatures.
• Laboratories: For precise temperature control in experiments, incubators, and storage freezers in research, medical, and analytical laboratories.
• Power Generation: Monitoring temperatures in turbines, boilers, and other critical equipment in power plants to ensure efficient and safe energy production.
• Pharmaceutical Manufacturing: For precise temperature control during drug production, storage, and transportation (e.g. cold storage of heat-sensitive biologics), ensuring product efficacy and safety in pharmaceutical facilities.
• Automotive Industry: Monitoring engine temperatures, exhaust gas temperatures, and other critical parameters in vehicle testing and manufacturing processes.

Your Trusted Temperature Probe Supplier & Manufacturer

RS Australia is a trusted and widely utilised supplier and distributor of temperature probes and other Test & Measurement solutions, from infrared thermometers to thermal imaging cameras. We offer an extensive range of temp probes, high temperature probes, and industrial temperature sensors from leading global brands like Chauvin Arnoux, Hanna Instruments, Keysight Technologies, and our in-house RS PRO line.

Our comprehensive selection ensures you can find the ideal probe for temperature to meet the specific demands of your application, whether it's for industrial automation, scientific research, HVAC systems, and beyond.

Choose RS Australia as your temperature probe supplier and enjoy numerous advantages such as quality assurance, convenient user-friendly procurement platforms, expert advice, and fast and reliable delivery. For more details on delivery services and fees, please refer to our Delivery Page.