Thermistors

A thermistor, short for ‘thermal resistor’, is a temperature sensing element composed of a mix of metal and metal oxide semiconductor materials. Typically, thermistors exhibit negative temperature coefficients (NTC), meaning their resistance decreases as their temperature rises. This characteristic forms the basis of their temperature sensing capability.

Thermistors are a cost-effective, yet highly accurate, alternative to other temperature sensors. They are available in various forms, including disc, bead, rod, or chip, and are usually encapsulated in epoxy resin, paint, glass or phenolic. This encapsulation allows them to be easily mounted or fixed within systems requiring temperature monitoring.

How Does a Thermistor Work?

Unlike conventional temperature sensing devices that directly display temperature, a thermistor functions by exhibiting a change in its electrical resistance in response to temperature variations.

The amount of change in resistance is determined by the sensing material within the thermistor and the medium being measured. The need to measure the temperature of a solid, liquid, or gas typically influences the selection of the most suitable material for optimal performance of the thermistor sensor.

To utilise a thermistor for temperature regulation, a temperature controller is used to monitor the thermistor's resistance, which directly correlates to its temperature. The controller then sends a signal to a heater or cooler to maintain the desired temperature of the thermistor probe and the system being monitored.

While the primary application of thermistors lies in their use as resistive temperature sensors, they can also be connected in series with other electrical components or devices to manage the flow of electrical current.

Types of Thermistors

NTC (Negative Temperature Coefficient) Thermistors

NTC thermistors are characterised by a decrease in electrical resistance as their temperature rises. An NTC sensor is commonly used as a temperature sensor, providing accurate temperature measurements. Additionally, NTC probes can be connected in series within a circuit to function as inrush current limiters, protecting sensitive components during power-up.

PTC (Positive Temperature Coefficient) Thermistors

Conversely, PTC thermistors exhibit an increase in electrical resistance as their temperature rises. PTC temperature sensors are commonly installed in series within circuits and serve as resettable fuses to protect against overcurrent conditions.

Factors to Consider When Selecting a Thermistor Temperature Sensor

When choosing a thermistor sensor, several key factors should be taken into account to ensure optimal performance in your application:

• Resistance-temperature characteristics: Understanding how the thermistor's resistance changes in relation to temperature variations is crucial for accurate temperature sensing and control within your system.
• Tolerance and accuracy: Consider the level of precision required for your specific application, as the tolerance and accuracy of the thermistor will directly impact the reliability of temperature measurements.
• Operating temperature range: Select a thermistor probe or sensor that can reliably withstand the full range of environmental temperatures it will be exposed to during operation in its intended application.
• Physical configuration: Thermistors come in various forms, such as bead, disc, or probe types, so choose a configuration that is physically suitable for the mounting requirements and the specific application environment.

Avoid Common Pitfalls When Purchasing Thermistors

When purchasing thermistors, it's important to be aware of and avoid these common mistakes to ensure you select the right component for your needs:

• Overlooking specifications: If the thermistor's specifications, such as its operating temperature range and resistance-temperature characteristics, do not align precisely with the application's demands, it can lead to inaccurate or unreliable performance.
• Incompatible tolerances: Selecting thermistors with tolerance levels that are not appropriate for the required precision of your application can result in inaccurate temperature readings and potentially compromise the system's functionality.
• Neglecting environmental factors: The operating environment's conditions, such as humidity, extreme temperatures, and potential exposure to chemicals, can significantly impact a thermistor sensor's performance and lifespan, so these factors must be considered.
• Assuming interchangeability: It's crucial to recognise that not all thermistors are directly interchangeable, as differences in their material composition and design can lead to variations in their performance characteristics and suitability for a given application.

Industry Applications of Thermistors

Due to the versatility and effectiveness of thermistors, they are used in many temperature sensing applications, such as:

• Digital thermometers: NTC thermistors are commonly used in digital thermometers for accurate body temperature readings due to their high sensitivity in the human body temperature range.
• Automotives: In vehicles, thermistor sensors, often NTC types, are used to measure the temperature of engine oil and coolants, providing crucial data for engine management systems.
• Ovens: Thermistor probes, including NTC and PTC thermistors, are employed in ovens to monitor and regulate cooking temperatures, ensuring precise heat control.
• Refrigerators: NTC sensors are frequently used in refrigerators to monitor and control internal temperatures, helping to maintain optimal food storage conditions and energy efficiency.
• Heating or cooling protection circuits: PTC sensors are often used in heating or cooling protection circuits as resettable fuses, limiting current in over-temperature conditions to prevent damage.

Your Trusted Thermistors Supplier and Manufacturer

For a comprehensive selection of high-quality thermistors, including NTC and PTC options, RS Australia is your reliable partner. As a trusted supplier, distributor, and manufacturer, we source our thermistor sensors from leading brands like EPCOS, Amphenol Advanced Sensors, and TE Connectivity, assuring excellent product quality.

Alongside our range of thermistors and thermistor probes, you'll discover a wide array of other electrical tools and devices, such as reed switches and DC power connectors, making us your convenient single source for all project essentials.

Explore our user-friendly website today and benefit from our efficient delivery services tailored to your project timelines. To know more about our delivery options, please visit our delivery information page.