What Does a Thermistor Do and How It Works

What Does a Thermistor Do?

A thermistor is a sensor that measures temperature.

It converts changes in temperature into accurate voltage changes.

Thermistors are used in temperature control systems to adjust the current through a Peltier device in order to maintain a setpoint temperature.

They can be embedded in or surface-mounted on the device needing temperature monitoring.

Thermistors can measure liquids, gases, or solids, and there are two main types: positive temperature coefficient (PTC) and negative temperature coefficient (NTC).

They are beneficial for their high sensitivity and accuracy in measuring temperature changes.

Key Points:

  • A thermistor is a temperature sensor that measures temperature.
  • It converts temperature changes into voltage changes.
  • Thermistors are used in temperature control systems for maintaining setpoint temperature by adjusting current through a Peltier device.
  • They can be embedded in or surface-mounted on the device needing temperature monitoring.
  • Thermistors can measure liquids, gases, or solids and there are two main types: PTC and NTC.
  • They offer high sensitivity and accuracy in measuring temperature changes.

Did You Know?

1. The first thermistor was developed in the 1930s by Samuel Ruben and was made of copper oxide.
2. Thermistors are utilized in automotive applications to monitor coolant temperature, ensuring proper engine performance and preventing overheating.
3. Some thermistors can be used to measure humidity levels by sensing changes in their resistance due to moisture in the air.
4. In the medical field, thermistors are commonly used in digital thermometers to measure body temperature accurately and quickly.
5. Thermistors are also employed in household appliances like ovens and refrigerators to regulate temperature for optimal functioning, enhancing food safety and preventing overheating.

Introduction To Thermistors

Thermistors are sensors used to measure temperature. They come in various shapes and sizes, including disk, chip, bead, or rod, and can be surface-mounted or embedded in a system. When using thermistors, it is important to consider the connection to the monitored device. For accurate temperature readings, the connection must be made using a thermally conductive paste or epoxy glue that is not electrically conductive.

Types And Shapes Of Thermistors

Thermistors are available in different types and shapes to suit various applications. They can be categorized into two main types: positive temperature coefficient (PTC) and negative temperature coefficient (NTC) thermistors. PTC thermistors exhibit an increase in resistance with rising temperatures, while NTC thermistors display a decrease in resistance. The selection of the thermistor type depends on the specific technical requirements and temperature range of the device being monitored.

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Shapes of thermistors can vary depending on the application. Common shapes include disk, chip, bead, or rod. These different shapes and sizes allow for flexibility in placement and integration into temperature control systems. Whether surface-mounted or embedded, the thermistor’s placement is crucial for both stability and accuracy.

Connection And Placement Of Thermistors

The connection to the monitored device is crucial for accurate temperature measurements. To establish a reliable thermal connection while maintaining electrical insulation, thermistors require a thermally conductive paste or glue. Care must be taken in creating this connection to avoid any electrical conduction that can lead to erroneous readings.

The placement of the thermistor within the system is also critical. To maintain stability, it should be positioned close to the thermoelectric or resistive heater. This proximity helps minimize temperature gradients and ensures that the thermistor accurately reflects the temperature of the heating element. To achieve precision, it is advisable to place the thermistor near the device that requires temperature control. This ensures that the thermistor is measuring the actual temperature of the target device, enabling precise control.

Thermistors In Temperature Control Systems

In temperature-controlled systems, thermistors are essential components used to measure the temperature of a device. A temperature controller monitors the temperature of the thermistor and communicates with a heater or cooler to maintain the desired temperature. This feedback loop allows the temperature controller to accurately adjust the heating or cooling to ensure a stable and controlled environment.

To achieve effective temperature control, thermistors are electronically connected to a Peltier device, also known as a thermoelectric cooler. The Peltier device regulates temperature by providing heating or cooling as required. A heatsink is typically attached to the Peltier device to aid in heat dissipation and improve overall efficiency.

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Thermistors And Temperature Controllers

The temperature sensors, like thermistors, send temperature feedback to the temperature controller using a small amount of current known as bias current. This feedback allows the temperature controller to make precise adjustments and maintain the desired temperature within the system.

Thermistors work best within a specific temperature range. Generally, they are reliable between -55°C and +114°C. However, they may not be suitable for extremely high or low temperatures. It is important to consider the technical specifications of the device being monitored before selecting a thermistor to ensure accurate readings and optimal performance.

Steinhart-Hart Equation And Thermistors

The Steinhart-Hart equation is a mathematical model used to convert thermistor resistance to temperature. It calculates the actual resistance of a thermistor as a function of temperature, utilizing coefficients provided by thermistor manufacturers. This equation, developed by John S. Steinhart and Stanley R. Hart in 1968, allows for accurate temperature measurements based on the resistance changes of the thermistor.

By applying the Steinhart-Hart equation, thermistors can provide high sensitivity and accuracy in measuring temperature changes. They are particularly useful for maintaining specific temperatures and tracking temperature shifts within a range of 50°C from ambient conditions. Thermistors can be embedded within devices or surface-mounted to monitor the temperature of liquids, gases, or solid objects.

Thermistors are invaluable sensors used to measure temperature in a wide range of applications.

Thermistors come in different types, shapes, and sizes, allowing for flexibility in integration. The correct connection and placement of thermistors are crucial for stable and accurate temperature readings. When used in temperature control systems, thermistors work in conjunction with temperature controllers to provide precise regulation. The Steinhart-Hart equation enhances their functionality, enabling accurate temperature measurements based on resistance changes.

  • Thermistors can convert resistance to temperature.
  • They provide high sensitivity and accuracy in temperature measurements.
  • Thermistors can be used to maintain specific temperatures and track temperature shifts.
  • They can monitor the temperature of liquids, gases, or solid objects.

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Frequently Asked Questions

What is a thermistor and how does it work?

A thermistor is an electronic component that acts as a resistor whose value changes in response to temperature variations. It can either increase or decrease its resistance with changes in temperature. This change in resistance is determined by a coefficient, denoted as ‘k’, which depicts the relationship between resistance and temperature. By monitoring the thermistor’s resistance, one can measure the corresponding temperature accurately, making it a valuable tool in various applications, including temperature control and monitoring systems. This responsiveness to temperature fluctuations makes thermistors highly suitable for detecting and regulating heat levels in electronic devices and systems.

What does a thermistor do GCSE physics?

A thermistor, in the realm of GCSE physics, serves as a temperature sensor by adjusting its resistance according to temperature variations. When subjected to lower temperatures, the thermistor exhibits a higher resistance, limiting the flow of current through it. However, as the temperature increases, the resistance of the thermistor decreases, enabling a greater current to pass through. This unique characteristic makes thermistors valuable components in various applications such as fire alarms, where they are employed to detect temperature changes and trigger appropriate responses.

What is the effect of thermistor?

Thermistors have a significant effect on electrical current due to their temperature-dependent resistance. Unlike regular resistors, thermistors vary their resistance based on the temperature. This characteristic enables them to be used for various applications such as temperature sensing, temperature compensation, and thermal control systems. By accurately measuring changes in resistance, thermistors can precisely monitor temperature variations and provide valuable information for controlling and regulating electronic devices and systems.

Is a thermistor a temperature sensor?

Yes, a thermistor is indeed a temperature sensor. Unlike thermocouples, which generate voltage based on temperature gradients, a thermistor directly measures temperature by monitoring changes in resistance. As the temperature increases or decreases, so does the resistance of the thermistor. This property allows it to accurately sense and indicate temperature variations, making it a reliable and widely-used sensor in various applications such as HVAC systems and electronic devices.

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