Select the Right Sensor for Your Application
Choosing a sensor type for your business is an important decision. Different sensors have varying levels of accuracy, temperature ranges, and are suitable for different applications.
Understand the difference between thermocouple, NTC thermistor and RTD/PT100 sensors so you can select the best one for your business and get the best results.
If you have any questions we haven't answered, please don't hesitate to get in touch with our sales team.
Thermocouple Sensors
ETI manufactures an extensive range of type K or T thermocouple probes that are compatible with our thermometers and data loggers.
Thermocouple probe options
Response time
Response time is the time it takes for a sensor to reach 66% (two-thirds) of its final temperature reading. This is the industry standard for measuring probe performance.
To reach virtually the full reading (around 99-100%), allow approximately five times the quoted response time.
Response times vary depending on the application. Factors such as the material being measured and, for liquids and gases, the amount of movement or stirring will affect how quickly the sensor responds.
The response times shown in our product listings were measured in a stirred oil bath under controlled conditions. Your actual response time may be faster or slower depending on your application, so these figures should be used as a guide.
PVC & PU coiled leads
Most probes are supplied as standard with a 1 metre straight PVC lead and connector. PVC is a general-purpose lead material and is available in lengths of up to 100 metres.
If you need greater flexibility, a 1 metre coiled PU lead is available as an alternative.
When ordering by telephone or email, replace the first digit (1) of the order code with 3 to specify a coiled PU lead.
The maximum operating temperature for both PVC and PU leads is 80 °C.
Stainless steel braided leads
Some industrial and high-temperature probes are fitted with a fibreglass-insulated, stainless steel over-braided lead for use in higher-temperature applications.
Where supplied as standard, the lead is 2 metres long and includes a connector.
The maximum operating temperature for the lead is 350 °C.
Applications
The applications listed for each probe are intended as a guide. Many probes are suitable for a wide range of uses beyond those shown.
If you're unsure which probe is right for your application, our team is happy to help. Contact us on +44 (0)1903 202151 or sales@etiltd.com for advice.
If a standard probe doesn't meet your requirements, we can also design and manufacture a bespoke solution.
RTD/PT100 Sensors
Resistance temperature detector probes are slower to respond to changes in temperature than thermocouple probes, but are generally more accurate.
RTD/PT100 probe options
Resistance temperature detectors
Resistance temperature detector (RTD or PT100) probes use a platinum sensor to measure temperature. As the temperature changes, the electrical resistance of the sensor changes in a predictable way, allowing the temperature to be measured accurately.
RTDs are known for their excellent accuracy, stability and repeatability, making them ideal for many industrial and laboratory applications.
Lead types
PVC leads are general-purpose and available in lengths of up to 100 metres.
Stainless steel braided leads are designed for high-temperature applications. With fibreglass insulation, they can be used at temperatures up to 350 °C.
PU coiled leads are also available as an alternative option where added flexibility is required.
Where appropriate, probes are supplied with a 1 metre straight PVC lead and connector as standard. PVC and PU leads have a maximum operating temperature of 80 °C.
Applications
The applications listed for each probe are intended as a guide. Many probes are suitable for a wide range of uses beyond those shown.
If you're unsure which probe is right for your application, our team is happy to help. Contact us on +44 (0)1903 202151 or sales@etiltd.com for advice.
If a standard probe doesn't meet your requirements, we can also design and manufacture a bespoke solution.
Thermocouple vs RTD Sensors
RTD (Pt100) sensors and thermocouples both measure temperature, but are suited to different applications.
RTDs are preferred where high accuracy, stability and repeatability are required, particularly at lower and moderate temperatures (typically below 600 °C).
Thermocouples are more cost-effective and can measure a much wider temperature range, including very high temperatures. However, they are generally less accurate and may drift over time, which can increase calibration requirements.
In summary, RTDs are best for precision measurement, while thermocouples are better suited to high-temperature or cost-sensitive applications.
Measurement range
Thermocouples are suitable for a wide temperature range and are ideal for high-temperature applications. Some types can measure temperatures above 1800 °C, making them highly versatile.
RTDs are designed for lower temperature ranges and are typically used up to around 600 °C.
Accuracy
RTDs offer the highest accuracy of the two sensor types, typically achieving around ±0.05 to ±0.1 °C when using Class A, 1/3 DIN, 1/5 DIN or 1/10 DIN elements with 3- or 4-wire construction.
Thermocouples are generally less accurate. However, high-accuracy Type K thermocouple probes can be manufactured using Class 1 wire, delivering an accuracy of around ±0.5 °C between 0 °C and 100 °C.
Drift
RTD sensors have a low risk of drift due to their design, making them highly stable over long periods.
Thermocouples are more prone to drift over time. This can be caused by ageing of the thermocouple wire, temperature cycling, or exposure to excessive heat.
For this reason, regular calibration should be considered as part of a planned maintenance programme.
Construction
Thermocouples typically have a faster response time due to the low mass of the junction. Response can be improved further by using a grounded or exposed hot junction, which allows quicker heat transfer.
RTD sensors generally respond more slowly because the sensing element measures temperature across the platinum film or wire-wound element, rather than at a single point. However, as RTD designs continue to become smaller, response times are improving.
Cost
Thermocouples are generally less expensive than RTD sensors. However, thermocouples will require regular calibration, which adds to the long-term costs of the product.
Thermistor Sensors
Thermistor probes measure temperature through changes in electrical resistance. They use NTC (negative temperature coefficient) sensors, meaning resistance decreases as temperature increases.
They offer good accuracy within a limited temperature range and provide fast response times due to their small size.
Compared with other sensor types, thermistors are typically faster to respond than RTD (Pt100) probes but slower than thermocouples.
They are generally not recommended for surface temperature measurement.
Thermistor probe options
Tolerance specification
Thermistor probe accuracy varies across the operating temperature range.
The tolerance at different points is shown below:
- ±0.4 °C between -20 & 100 °C
- ±0.3 °C between -10 & 0 °C
- ±0.2 °C between 0 & 70 °C
- ±0.4 °C between 70 & 100 °C
Lead types
PVC leads are general-purpose and suitable for everyday use.
FEP (fluoroethylene-propylene) leads are designed for low-temperature applications and can be used in sub-zero environments down to -100 °C.
Where appropriate, probes are supplied with a 1 metre straight PVC lead and a compatible Lumberg or Binder connector.
PVC and PU leads have a maximum operating temperature of 80 °C.
Applications
The applications listed for each probe are intended as a guide. Many probes are suitable for a wide range of uses beyond those shown.
If you're unsure which probe is right for your application, our team is happy to help. Contact us on +44 (0)1903 202151 or sales@etiltd.com for advice.
If a standard probe doesn't meet your requirements, we can also design and manufacture a bespoke solution.
Ready to Explore Probes?
Now you've chosen your sensor, it's time to choose your probe type. View our guide to explore the different options for measuring surfaces, fridges, food and more.
Frequently asked questions
What types of probe sensor does ETI make?
ETI makes Thermocouple, Themistor, PT 100/RTD and bespoke probes. For any special requests take a look at our Bespoke Probes page.
What’s the difference between a sensor and a probe?
A sensor is the component that actually measures temperature, while a probe is the complete assembly that houses the sensor and allows it to be used in a practical application. The probe protects the sensor and ensures it can be placed correctly in the measurement environment.
Which temperature sensor is the most accurate?
RTD (Pt100) sensors generally offer the highest accuracy, typically achieving around ±0.05 to ±0.1 °C. They are designed for precise, stable measurements, particularly in laboratory and industrial applications.
Why do different sensors have different temperature ranges?
Different sensor types are built using different materials and construction methods, which determine their operating limits. For example, thermocouples can withstand very high temperatures, while thermistors and RTDs are optimised for lower or medium ranges where accuracy and stability are more important.
Which sensor type is best for high temperatures?
Thermocouples are best suited for high-temperature applications. Certain types can measure temperatures above 1800 °C, making them ideal for industrial processes where extreme heat is involved.
How do I choose between an RTD, thermocouple or thermistor?
It depends on the application. RTDs are best for high accuracy and stability at lower to medium temperatures. Thermocouples are suited to wide or high-temperature ranges where durability and cost-effectiveness are important. Thermistors offer high sensitivity and fast response but operate over a more limited temperature range.