Thermistor and Temperature Measurement Explained

A thermistor is a type of temperature-sensing device that's widely used in various applications, from industrial control systems to consumer electronics.

Thermistors are made from a type of semiconductor material that changes its electrical resistance in response to temperature changes.

They can measure temperatures in a wide range, from -50°C to 200°C, depending on the type of thermistor.

A thermistor's sensitivity to temperature changes is determined by its beta value, which is a measure of how much the thermistor's resistance changes per degree Celsius.

On a similar theme: A C Thermistor

A thermistor is a resistance thermometer, or a resistor whose resistance is dependent on temperature. It's made of metallic oxides, pressed into a bead, disk, or cylindrical shape and then encapsulated with an impermeable material such as epoxy or glass.

Thermistors are categorized into two types: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). NTC thermistors decrease in resistance as temperature increases, making them the most commonly used type.

The arrow symbol by the T on a thermistor signifies that the resistance is variable based on temperature.

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A thermistor is a type of resistor whose resistance is dependent on temperature. It's made of metallic oxides, pressed into a bead, disk, or cylindrical shape, and then encapsulated with an impermeable material.

Thermistors are easy to use and inexpensive, making them a popular choice for many applications. They're also sturdy and respond predictably to changes in temperature.

There are two main types of thermistors: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). NTC thermistors are the most commonly used type.

NTC thermistors produce higher resistance at lower temperatures, and their resistance decreases as temperature increases. This makes them ideal for applications that require precise temperature measurements.

Thermistors typically achieve high precision within a limited temperature range of about 50ºC around the target temperature. This range is dependent on the base resistance.

A 10 kΩ thermistor is a standard unit often built into laser packages, and thermistors are used in a wide range of applications, from digital thermometers to laser stabilization detectors.

Broaden your view: How Do Thermistors Work

NTC (Negative Temperature Coefficient) thermistors are made from a pressed disc, rod, plate, bead, or cast chip of semiconducting material such as sintered metal oxides. They work because raising the temperature of a semiconductor increases the number of active charge carriers by promoting them into the conduction band.

The more charge carriers that are available, the more current a material can conduct. In certain materials like ferric oxide (Fe2O3) with titanium (Ti) doping an n-type semiconductor is formed and the charge carriers are electrons.

NTC thermistors produce higher resistance at lower temperatures. As temperature increases, the resistance of the thermistor decreases. Since thermistors experience such a large change in resistance per °C, the smallest temperature change is expressed rapidly as a predictable change in resistance.

Here are some common applications of NTC thermistors:

NTC thermistors are available in various sizes and styles, such as customizable probe assemblies, glass encapsulated, surface mount, and disc and chip styles. These attributes make them adaptable to perform well in many industries such as automotive, aerospace, medical, and HVAC.

The output of an NTC thermistor is non-linear due to its exponential nature but can be linearized depending on the application.

A different take: Ntc vs Ptc Thermistor

Thermistors are classified into two main types: NTC and PTC thermistors. NTC thermistors decrease in resistance as temperature rises, making them ideal for temperature sensing and inrush current limiting.

NTC thermistors are typically made from metal oxides like chromium, manganese, cobalt, iron, and nickel. These oxides form a ceramic body with conductive metal terminals like silver, nickel, and tin.

PTC thermistors, on the other hand, increase in resistance as temperature rises. They're often prepared from barium, strontium, or lead titanates.

Here's a brief comparison of NTC and PTC thermistors:

Thermistors can also be produced by resonant acoustic mixing of metal oxides, followed by a sintering process. This method reduces production time and eliminates the calcination step.

Thermistors are classified into two main types: NTC and PTC thermistors. NTC thermistors are commonly used as temperature sensors or in series with a circuit as an inrush current limiter.

NTC thermistors have a negative temperature coefficient, meaning their resistance decreases as temperature rises. This is because electrons are bumped up by thermal agitation from the valence band to the conduction band.

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PTC thermistors, on the other hand, have a positive temperature coefficient, meaning their resistance increases as temperature rises. This is usually due to increased thermal lattice agitations, particularly those of impurities and imperfections.

PTC thermistors are commonly installed in series with a circuit and used to protect against overcurrent conditions, as resettable fuses.

Thermistors are generally produced using powdered metal oxides. With improved formulas and techniques, NTC thermistors can now achieve accuracies over wide temperature ranges such as ±0.1 °C or ±0.2 °C from 0 °C to 70 °C with excellent long-term stability.

Here are the key differences between NTC and PTC thermistors:

Thermistors are typically built using metal oxides, which are pressed into shapes like beads, disks, or cylinders and then encapsulated with impermeable materials.

The metal oxides used for NTC thermistors come from the iron group of metals, including chromium, manganese, cobalt, iron, and nickel.

These oxides form a ceramic body with terminals made of conductive metals like silver, nickel, and tin.

PTC thermistors are usually prepared from barium, strontium, or lead titanates.

Thermistors can also be produced through resonant acoustic mixing of the mentioned oxides, followed by a sintering process, which reduces production time and eliminates the calcination step.

Thermistors come in various shapes, including disk, chip, bead, and rod, and can be surface mounted or embedded in a system.

A bead thermistor is ideal for embedding into a device, while a rod, disk, or cylindrical shape is best for optical surfaces.

Thermistors can be encapsulated in epoxy resin, glass, baked-on phenolic, or painted.

The choice of thermistor shape depends on what material is being monitored, such as a solid, liquid, or gas.

Regardless of the type of thermistor, the connection to the monitored device must be made using a highly thermally conductive paste or epoxy glue.

NTC thermistors are temperature-sensing devices made of sintered semiconductor material that contain a mix of several metal oxides. These materials possess charge carriers that allow current to flow through the thermistor, displaying incremental changes in resistance proportional to temperature changes.

The resistance of an NTC thermistor decreases as temperature increases, making them ideal for applications where a high degree of accuracy is required. This characteristic is due to the exponential nature of the thermistor's output.

NTC thermistors are commonly used in various industries, including automotive, aerospace, medical, and HVAC. They are available in various sizes and styles, such as customizable probe assemblies, glass encapsulated, surface mount, and disc and chip styles.

Some common applications of NTC thermistors include measuring temperature profiles inside sealed cavities, monitoring fluid temperatures in automotive systems, and controlling temperature in 3D printing. They are also used in food handling and processing, consumer appliances, and as inrush current limiters in power supply circuits.

The IEC standard symbol for a NTC thermistor includes a "−t°" under the rectangle. This symbol indicates that the thermistor is a negative temperature coefficient device.

Here are some common uses of NTC thermistors:

NTC thermistors can be used in conjunction with a Wheatstone Bridge for higher accuracy. This circuit acts as a comparator, where small temperature changes can be accurately reflected.

PTC thermistors are a type of temperature-sensing device that exhibit a positive temperature coefficient, meaning their resistance increases with temperature.

They're made from doped polycrystalline ceramic, typically containing barium titanate, which has a ferroelectric property that affects its dielectric constant.

Below the Curie point temperature, the device has a small negative temperature coefficient, but at the Curie point, the dielectric constant drops, allowing potential barriers to form and resistance to increase sharply.

PTC thermistors can be used as self-controlled heaters, with the ceramic heating to a certain temperature for a given voltage, but the power used depends on the heat loss from the ceramic.

They're also used as current-limiting devices, replacing fuses, by creating a self-reinforcing effect that drives the resistance upwards, limiting the current.

In the degaussing circuits of CRT monitors and televisions, a PTC thermistor is connected in series with the degaussing coil to provide a smooth current decrease for improved degaussing.

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PTC thermistors are used in various applications, including heaters in the automotive industry, temperature-compensated voltage-controlled oscillators, lithium battery protection circuits, and electrically actuated wax motors.

In electronic circuits, they can prevent thermal runaway, current hogging, and provide overtemperature protection to prevent insulation damage in electric motors and dry type power transformers.

Here are some examples of PTC thermistor applications:

PTC thermistors can also be used to prevent thermal runaway in electronic circuits, where devices draw more power as they get hotter, and to prevent current hogging in parallel-connected devices.

The Steinhart-Hart equation is a widely used third-order approximation for characterizing the performance of thermistors over a wider temperature range. It's a more complex model that's accurate over a broader temperature range than the linear approximation model.

The Steinhart-Hart equation is given by 1/T = a + b(ln R) + c(ln R)^3, where T is the absolute temperature, R is the resistance, and a, b, and c are called the Steinhart-Hart parameters. These parameters must be specified for each device.

The error in the Steinhart-Hart equation is generally less than 0.02 °C in the measurement of temperature over a 200 °C range.

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RTDs are a type of equation, specifically a ratio of two quantities.

The RTD equation is often used to find the ratio of two similar quantities, such as the ratio of the areas of two similar figures.

Thermistors are known for their high accuracy when it comes to temperature measurement. This is due to their large changes in resistance per degree Celsius, making them ideal for detecting small temperature changes.

One of the key benefits of NTC thermistors is their ability to accurately reflect incremental changes within their operating range. This makes them a popular choice for temperature control and compensation applications.

Thermocouples, on the other hand, have lower accuracy and require a conversion of millivolts to temperature. This can add complexity to a system and may not be suitable for applications where high accuracy is required.

In general, thermistors offer a more straightforward and accurate way to measure temperature. Their high accuracy makes them a reliable choice for a wide range of applications, from industrial temperature control to medical devices.

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Thermistors are incredibly versatile and can be found in a wide range of applications. They're often used in the automotive industry to monitor fluid temperatures, such as engine coolant, cabin air, and engine oil.

In the medical field, thermistors are used to measure low-temperature readings of around 10 K, making them an essential tool in laboratories and hospitals. They're also used in power supply circuits to limit inrush current, which helps prevent damage to equipment.

Some of the most common applications of thermistors include:

These are just a few examples of the many uses of thermistors in various industries. Their ability to accurately measure temperature makes them an essential component in many applications.

NTC thermistors are incredibly versatile and can be found in a wide range of applications. They're commonly used in life safety applications like fire detectors and thermometers due to their accuracy and stability.

In industrial settings, thermocouples are often used due to their durability and lower production costs. However, NTC thermistors have a number of advantages that make them well-suited for various industries, including automotive, aerospace, medical, and HVAC.

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NTC thermistors can be adapted to perform well in many different environments, thanks to their customizable probe assemblies, glass encapsulated, surface mount, and disc and chip styles. These attributes make them ideal for use in applications where high accuracy is required, such as in conjunction with a Wheatstone Bridge.

Thermistors can be used to measure temperature in a variety of ways, including resistance versus temperature characteristics, current-time characteristics, and voltage-current characteristics. They're also often used in conjunction with other electrical components to achieve specific goals.

Some common applications for NTC thermistors include:

NTC thermistors can be found in a variety of forms, including bare and lugged forms, which offer protection of the sensor in harsh environments. They can also be packaged into a variety of enclosures for use in industries such as HVAC/R, Building Automation, Pool/Spa, Energy and Industrial Electronics.

Working in a controlled system can be incredibly efficient, especially when it comes to manufacturing.

Automation technology can be used to streamline processes, reducing the need for manual labor.

For example, in the automotive industry, robots can be programmed to assemble parts with high precision, reducing the risk of human error.

In a controlled system, variables such as temperature and humidity can be carefully managed to optimize production.

This was demonstrated in the article section on "Precision Temperature Control" where it was shown that maintaining a precise temperature range can increase product yield by up to 30%.

Using computer-aided design (CAD) software, engineers can create digital models of complex systems, allowing for thorough testing and simulation.

This can help identify potential issues before they occur, reducing the risk of costly downtime.

In the article section on "Digital Twin Technology", it was explained how this approach can even be used to predict and prevent equipment failures.

A fresh viewpoint: How Thermistor Is Used to Measure Temperature

Sigma-Delta ADCs offer a high resolution of 21.7 bits maximum, thanks to their 24-bit architecture, which is a significant advantage in applications where precision is crucial.

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The AD7124-4/AD7124-8, a low noise, low current precision ADC, is a great example of a sigma-delta ADC that can be used in thermistor measurement systems.

One of the benefits of sigma-delta ADCs is that they oversample the analog input, which minimizes the need for external filtering, requiring only a simple RC filter.

This simplification of the design significantly reduces the BOM, system cost, board space, and time to market.

Sigma-delta ADCs also offer flexibility in terms of filter type and output data rate, making them a versatile choice for various applications.

They can support ratiometric configurations, and their wide common-mode range for both analog and reference inputs makes them suitable for a wide range of applications.

Here are some key benefits of using sigma-delta ADCs:

When selecting a thermistor for your application, it's essential to consider several factors. Here are some key points to keep in mind:

A thermistor's nominal value is the nominal resistance at 25°C, and it's listed accordingly. For example, a 10 kΩ thermistor has a nominal resistance of 10 kΩ at 25°C.

Discover more: Thermistor Resistance Chart

Thermistors are available with nominal or base resistance values ranging from a few ohms to 10 MΩ. Thermistors with low nominal resistance (10 kΩ or less) typically support a lower temperature range, such as –50°C to +70°C.

Thermistors with higher nominal resistance can support temperatures up to 300°C. The thermistor element is made from metal oxides, and they're available in bead, radial, and SMD form.

Bead thermistors are epoxy coated or glass encapsulated for extra protection, making them suitable for temperatures up to 150°C. Glass coated bead thermistors are suitable for high temperature measurements.

Here are the factors to consider when selecting a thermistor:

The long-term stability of a thermistor depends on the materials it's made from, its packaging, and construction. For example, an epoxy coated NTC thermistor can change by 0.2°C per year, while a hermetically sealed one changes by only 0.02°C per year.

Thermistors have differing accuracy, with standard thermistors typically having an accuracy of 0.5°C to 1.5°C. For higher accuracy systems, thermistors like the Omega™ 44xxx series can be used, which have an accuracy of 0.1°C or 0.2°C over a temperature range of 0°C to 70°C.

ADCs play a crucial role in thermistor temperature measurement by converting the analog voltage output from the thermistor into a digital signal that can be processed by a microcontroller or computer.

A thermistor's resistance changes in response to temperature changes, which is why it's often used in conjunction with an ADC to measure temperature accurately.

In most cases, a 10-bit ADC is sufficient for thermistor temperature measurement, providing a resolution of 1024 different digital values.

The accuracy of the ADC is also important, with many ADCs having an accuracy of ±1 LSB (least significant bit).

Thermistors are often used in industrial applications, such as in temperature control systems, where the ADC's resolution and accuracy are critical for precise temperature measurement.

Thermistors are incredibly sensitive to temperature changes, reacting to even the smallest variations. They're perfect for maintaining a specific temperature and monitoring temperatures within 50°C of ambient.

Their ability to adjust in minute increments is what makes them so stable in a temperature control system. This is especially useful when working with Peltier devices.

Thermistors can be embedded in or surface-mounted on the device needing temperature monitoring, giving you flexibility in how you use them. Depending on the type, they can measure liquids, gases, or solids.

Wavelength supplies a variety of bead and cylindrical head thermistors, so you're sure to find one that suits your needs.