Thermistor temperature sensor technical reference information

In our thermistor technical reference section you will find resource material covering all aspects of thermistors, from basic theory to types of thermistors, with further links to more detailed information.

If you have a question that isn't answered here, why not ask us via the contact form or call us. 

 

Table of contents

 

1. What is a Thermistor?

2. Thermistor Symbol

3. How do Thermistors work? 

4. What is B (Beta) constant (B value) in a thermistor

5. Typical Thermistor Element

6. NTC Thermistors

7. PTC Thermistors

8. Benefits of Thermistors over other temperature sensors

9. RTDs vs Thermistors Comparison Video

10. What different types of thermistor temperature sensors are available?

11. Made to order Thermistor probes 

12. Thermistor Resistance and Accuracy Specifications

 

 

 

1. What is a Thermistor?

A thermistor is semiconductor device, which is a temperature sensitive resistor, whose resistance varies with temperature. The name thermistor is and amalgamation of the words ‘thermal’ & ‘resistor’.

 

2. Thermistor Symbol

 Thermistor Symbol

 

3. How do Thermistors work?

Thermistors operate over a relatively small temperature range compared to other temperature sensors, such as RTDs and Thermocouples. They are generally very accurate, repeatable, interchangeable and precise within their narrow temperature range, typically 0-200°C.

Thermistors are normally specified at 25°C and have an R-T curve with high nominal resistance values, typically between 1,000 to 10,000 Ω and even higher in some cases.

 

4. What is B (Beta) constant (B value) in a thermistor

As it is a non-linear device the B constant in a thermistor is needed to identify it. This is the relationship in resistance in a thermistor between two specified points, normally 0-50C, 25/50C, 25/85C and is specified in Kelvin (K) which is calculated using the formula below (Fig 3.) 

Fig 3. b = Ln(R t1/ Rt2) / (1/T1 – 1/T2) 

This means in a 10,000 Ω (R25) thermistor, the B value can be 3435K. However, another manufacturers 10,000 Ω thermistor can have a B value of 2976K. 

Therefore thermistors can have the same reference resistance of 10,000 Ω at 25 Deg C (R25) but can have different B values, so both values are needed to identify a thermistor. 

Another way to calculate the Thermistor RT Curve is to use the Steinhart-Hart method. Which is explained in detail here

 

5. Typical Thermistor Element

A typical thermistor element when constructed as a temperature measurement probe only requires 2 wire connection due to the relatively low resistance of the lead wire.

 

Thermistor Symbol

 

6. NTC Thermistors

Negative temperature coefficient (NTC) thermistors have a resistance which reduces as the temperature rises (fig 1.). They are used for resistance thermometers in temperature measurement and all Sterling Sensors assemblies are made using this type of thermistor.

 NTC Thermistor temperature vs resistance

Fig 1. (NTC Thermistor graph)

 

7. PTC thermistors

Positive temperature coefficient thermistors have a resistance which rises as the temperature increases (Fig 2.) and are not used for temperature measurement. They are ideal as current and temperature limiting devices for circuit protection, such as Lithium batteries.

 PTC Thermistors

 

Fig 2. (PTC Thermistor graph)

 

8. Benefits of thermistors over other temperature sensors

Thermistor advantages and disadvantages

Advantages

• Highly accurate

• Low cost

• Repeatable

 Very responsive to changes in temperature

 

Disadvantages

• Narrow working temperature range (Typically 0-200°C) compared to other sensors such as RTDs and Thermocouples

 Susceptible to self-heating errors

 More fragile as they are semiconductor devices

 Extremely non-linear

 

9. RTDs vs Thermistor comparison video

A practical guide to help you choose the right product for your application.

10. What different types of Thermistor temperature sensors are available?

 

Thermistors

We a manufacture a range of NTC thermistor temperature sensing probes using high accuracy, interchangeable elements with excellent long term stability.

Thermistor probes can be supplied in 1k to 100k R25 values with various Beta values and tolerances on request. Our standard range uses a 10k NTC element and we can design and fabricate products to your specifications. Whatever your needs, Sterling Sensors will be able to provide a thermistor option for your application.

 

Fabricated Thermistors

This range of thermistor temperature probes uses fabricated sheaths to protect the thermistor element.

They are available with your choice of NTC thermistor element with a wide range of terminations, such as lead wires and a variety of plugs to suit a wide variety of applications.  

 

General Purpose Thermistors

Our general purpose thermistor temperature sensor range covers products for diverse applications, such as; indoor and exterior ambient temperature measurement, bearing sensors and bolt sensors.

 

Hand Held Thermistors

Sterling Sensors manufacture a wide range of handheld thermistor sensors for use with digital handheld thermometers for surface, air or insertion temperature measurement in various applications such as food, water, beverage, cold storage facilities or environmental monitoring

 

11. Made to order thermistor probes

As a specialist manufacturer, Sterling Sensors currently make thermistor probes to order for many UK and international customers at our purpose built factory in Manchester, UK. They can be made to your specification or we can propose a design, whether it's a one-off or a mass production run.

Discuss your application with our experienced sales engineers, who can guide you through the design and build of your thermistor sensors to ensure you find the right solution for your application.

 

12. Thermistor Resistance and Accuracy Specifications

Below is a table for our standard range of thermistor elements

 

Thermistor RT Reference Table

The PDF documents listed below have a table giving accurate resistance of Ohms per degree (°C) for thermistor reference

Image Map

 

Further information

For full technical characteristics of thermistors visit https://en.wikipedia.org/wiki/Thermistor

For more information on the history of thermistors visit http://www.temperatures.com/thermistors.html

 

Can't find what you need?

Give us a call on +44(0)161 620 0410 or email us: sales@sterlingsensors.co.uk

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