In this blog, we will delve into everything a beginner needs to know about thermistors, from their basic operation to their diverse applications.

What is a Thermistor?

A Thermistor is a kind of resistor that reacts to temperature changes by significantly changing its resistance. Thermistors are not like ordinary resistors in that they change resistance in response to temperature; instead, they provide a more or less constant resistance.

When Was the Thermistor Invented?

Historical records indicate that temperature-sensitive resistor development dates back to the late 19th and early 20th centuries, while the precise date of the thermistor's discovery is unknown. The early development of thermistor technology is attributed to several scientists, including Samuel Beckett and Samuel Ruben.

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What Does a Thermistor Do?

The main purpose of a thermistor is to translate changes in temperature into adjustments in electrical resistance. A thermistor's resistance usually rises (Positive Temperature Coefficient, or PTC thermistor) or falls (Negative Temperature Coefficient, or NTC thermistor) with increasing temperature. Electronic circuits can sense this change in resistance, which enables accurate temperature measurement.

Why Thermistor is Used?

Compared to alternative temperature sensors, thermometers have the following benefits:

• High Sensitivity: They allow for accurate readings because even slight temperature changes result in noticeable resistance changes.
• Fast Response Time: Thermistors are suited for applications needing real-time monitoring because of their ability to respond swiftly to temperature changes.
• Wide Temperature Range: Thermistors can function well across a wide range of temperatures, from cryogenic lows to extremely high temperatures.
• Small Size: Their small size makes it simple to incorporate them into a variety of gadgets and confined areas.
• Relatively Low Cost: Thermistors are a reasonably priced temperature-sensing solution because they are often low-cost components.

How Does a Thermistor Work?

The type of material used determines how a thermistor functions internally:

• NTC Thermistors: The most popular kind is NTC thermocouples. Usually, semiconductor materials like metal oxides are used to make them. Heat causes the atoms in the material to vibrate more, which obstructs the flow of electrons and reduces resistance.
• PTC Thermistors: Barium titanate is one of the materials used to make these thermistors. The material's granules split when it's cold, which prevents current flow. The grains get closer together as the temperature rises, making the route more conducive and raising resistance. 

How to Test a Thermistor?

The procedure for testing a thermistor is not too complicated. This is a fundamental method:

1. Assemble your equipment: A heat source (such as hot water or a soldering iron), a known-value resistor, and a multimeter in the resistance mode are required.
2. Link the thermocouple: Connect the multimeter probes to the leads of the thermistor.
3. Assuming room temperature, measure the resistance: Record the resistance reading.
4. Add some heat: The thermistor should be briefly exposed to the heat source.
5. Watch how the resistance shifts: For NTC thermistors, the resistance should go down, whereas for PTC thermistors, it should go up.
6. Compare with a known resistor: When comparing the thermistor to a known resistor, if there isn't much of a change in resistance or if the change is going the opposite way, there may be a problem. To obtain a general notion of its functionality, you can compare the measured resistance at room temperature with a known-value resistor of comparable resistance.

Note: For precise testing instructions and suggested techniques, refer to the datasheet for the thermistor.

How to Use Thermistor with Arduino?

Applications for temperature sensing can be developed by integrating thermoreceptors with microcontrollers such as Arduino.

An overview of utilizing an Arduino thermistor is provided here:

Assemble your supplies: A thermistor, an Arduino board, jumper wires, a resistor (10kΩ is usual), and a breadboard (optional) are required.

Link the circuit:

• Attach one leg of the thermistor to the Arduino's analog input pin (A0, for example).
• Attach the thermistor's other leg to a resistor.
• Attach the other end of the resistor to the 5V power pin on the Arduino.
• Attach the resistor's remaining leg to the ground.

Put the code online: To read the voltage from the thermistor and convert it to temperature, you'll need code. Thermistor-Arduino projects can be aided by a plethora of online information and example codes.

Adjust the sensor: Accurate temperature measurements are frequently dependent on sensor calibration because the thermistor's resistance-temperature connection is not always linear. To do this, you must take resistance readings at known temperatures and use the values obtained to build a conversion table or equation in your Arduino code.

Recall that this is only a rudimentary synopsis. Depending on your thermistor type and the specifications of your project, the precise code and component values will change. For comprehensive instructions and code samples, consult online tutorials and resources.

Can Thermistor Go Bad?

Yes, thermistors can break down for several causes, such as:

• Physical damage: The internal structure of the thermistor can be harmed by extreme heat, mechanical stress, or exposure to hostile environments, which will reduce its resistance.
• Degradation over time: Over time, the maximum operating temperature of some thermistors, especially PTC thermistors, may gradually drop.
• Manufacturing defects: Thermistor faults can be caused by defective parts or flaws in the production process.

A thermistor that isn't working properly can be found using the testing techniques previously discussed.

Can a Thermistor be Bypassed?

It could be feasible to get around a thermistor in a circuit in specific circumstances. However, for several reasons, this strategy is typically discouraged:

• Safety risks: Thermistors are frequently used to prevent overheating. Ignoring them may result in component damage or maybe fire threats if overheating is not detected.
• Functionality loss: A temperature measurement circuit's temperature sensing function will become inoperative if a thermistor is bypassed.
• Underlying issue: A thermistor that isn't working properly could be a sign of a more serious circuit problem. Ignoring it could cause the issue to appear worse and cause other issues.

To guarantee the safe and appropriate functioning of the circuit, it is always advised to identify the reason behind the thermistor malfunction and replace it if required.

Can a Thermistor be Repaired?

Thermistors are relatively cheap parts, and because of their small size and fragile manufacture, it is usually neither practicable nor economical to repair them. Replacing a malfunctioning thermistor is usually the best line of action.

When is Thermistor Used?

Thermistors' small size, quick response time, and great sensitivity make them useful in a variety of sectors. These are a few such usage cases:

• Temperature Measurement: Thermistors are extensively used to monitor and control temperature in industrial process control systems, thermometers, and thermostats.
• Overheating Protection: These are built into computers and battery packs, among other electronic devices, to identify overheating and stop harm.
• Flow Measurement: Thermistors can be used to detect temperature changes brought on by differences in flow rate, which allows for the measurement of fluid flow.
• Applications in Medicine: They are used in medical equipment such as fever detectors and thermometers.
• Automotive Applications: Thermistor sensors are employed in the detection of exhaust gas temperature, air intake temperature, and engine coolant temperature.

Conclusion

In the field of temperature sensing, resistors are useful and adaptable parts. They are appropriate for a range of applications in a variety of sectors due to their small size, quick reaction, and high sensitivity. You may use thermistors in your projects more skillfully and have a better understanding of their function in temperature measurement and control by learning about their operating principles, applications, and limitations.

FAQs

What is a thermistor used for?

Heat causes thermoreceptors, the temperature chameleons of resistors, to alter in resistance. They are therefore ideal for:

• Thermometers: Thermistors detect temperature changes in everything from your digital thermometer to medical equipment.
• Overheat Protection: They guard against overheating in computers and phones by acting as temperature guardians in devices.
• Flow Rate Sensing: By identifying temperature differences brought on by variations in flow, thermoreceptors may even determine the flow rate in liquids.

These little sensors are essential for maintaining temperature and smooth operation in a variety of applications.

What is the difference between a resistor and a thermistor?

The way a resistor and a thermistor react to temperature is where they diverge most:

• Resistor: The purpose of a standard resistor is to provide a reasonably constant resistance to the flow of electrical current. This resistance value is selected for a particular circuit and, within normal working ranges, usually does not fluctuate much with temperature swings.
• Thermistor: A thermistor, on the other hand, is a unique kind of resistor whose resistance varies with temperature. Thermistors come in two primary varieties:
  • NTC (Negative Temperature Coefficient): An NTC thermistor's resistance drops with temperature.
  • PTC (Positive Temperature Coefficient): A PTC thermistor's resistance rises with temperature.

Thermistors are useful in applications such as temperature measurement, control, and protection because of their temperature dependency.

What are some alternatives to thermistors?

There are numerous more temperature sensors available, each having pros and cons of their own. Infrared temperature sensors, resistance temperature detectors (RTDs), and thermocouples are a few substitutes. The requirements of the particular application, including the required precision, reaction time, and temperature range, all influence the choice of sensor.