What Is A Thermistor And What Does It Do?
Introduction
Do you want to know what a thermistor is, how does it work, where it is used, as well as the different types? Then you are in the right spot, we have answered all those questions and many more for you.
Enjoy your reading!
What is a thermistor?
A thermistor is a variable resistor, which resistance is dependent on temperature, comparing it to the standard resistors. It comprises of sintered semiconductor material which exhibits a change in resistance with a small change in temperature.
What does a thermistor look like?
The thermistor is a discrete device. Usually, it is very small in size. It looks like other electronic components, such as a resistor or a capacitor. Thermistors are made of metallic oxides, pressed into a bead, disk, or cylindrical shape and encapsulated with an impermeable material such as epoxy or glass.
What does a thermistor do?
A thermistor changes its resistance, according to the temperature it is immersed in. Some thermistors have a positive temperature coefficient where the resistance increases as temperature increases (PTC), while others have a negative temperature coefficient (NTC) where the resistance decreases as temperature increases.
What are the types of thermistors?
In general, thermistors are divided into two types based on their conduction model. The first type is “Negative Temperature Coefficient (NTC)” which has less resistance at higher temperatures. The second type is ‘’Positive Temperature Coefficient (PTC)”. It has more resistance at higher temperatures.
How does a NTC thermistor work?
Negative temperature coefficient thermistors, or NTC thermistors as we mentioned above, decreases their resistive value as the temperature increases. NTC thermistors are one of the most popular sensors in practice, due to the fact that they can be used in any type of equipment where temperature plays a role.
This type of thermistor has a large negative response, meaning that even a small change in the temperature can cause significant changes in their electrical resistance. As a result, this makes them perfect for accurate measurement and control of the temperature.
Another thing to keep in mind is their “β” value. It represents a material constant determined by the ceramic material from which it is made. It describes the gradient of the resistive (R/T) curve over a particular temperature range between two temperature points. Each thermistor material will have a different material constant and therefore a different resistance versus temperature curve.
How does a PTC thermistor work?
Positive temperature coefficient thermistors, or PTC thermistors, increase their resistive value as the temperature increases. They are made of polycrystalline ceramic materials which are in general, highly resistive in their original state. Moreover, they are made semi-conductive when dopants are added. They are mainly used as PTC self-regulating heaters. Their transition temperature is between 60 and 120 °C. However, there are special application devices that can switch as low as 0 °C or as high as 200 °C.
What is a thermistor used for?
Thermistors are inexpensive devices and are regularly used in electronic equipment. They are not as accurate as other types of sensors such as thermocouples or resistance thermometers.
In general, thermistors are used as inputs to digital thermometers. For example, in cars to measure oil and coolant temperatures. Moreover, they are used in many household appliances such as refrigerators, ovens, and more.
Instances of more sophisticated applications include optical blocks, and stabilisation detectors to name a few in which the thermistor is built in them.
How does a thermistor work?
The type of materials used in the thermistor dictates how much the resistance will change based on the temperature changes. Thermistors are nonlinear, which means that the connection between the temperature and resistance will not form a straight line, but rather a curve on a graph where the line sits and how much it changes depends on how the thermistor is made.
How thermistor is used to measure temperature?
The thermistor needs to be immersed in the temperature environment. Connection wires need to go back to the instrument. The instrument needs to be set up to match the thermistor type being used.
What does a thermistor do in a circuit?
The main purpose of a thermistor is to give a circuit the ability to sense changes in temperature. A thermistor is a component which has the ability to change its resistance as temperature changes.
Thermistor vs thermocouple – what is the difference between them?
Thermistors are lower-temperature devices and cheaper, while thermocouples are much more expensive and are used for higher-temperature devices. Thermistors are more stable in the long term than a thermocouple which can suffer from thermal drift.
What are the advantages and disadvantages of thermistors?
Advantages of thermistors
The first advantage of thermistors is that they are very cheap and are used in high-volume applications such as white goods. Another one is that they require only two wires going between the instrument and the sensor, whereas a resistance thermometer usually has three. Because thermistors are high-resistance devices, you do not usually need to consider the resistance of the connection wires going back to the instrument.
Disadvantages of thermistors
One disadvantage of thermistors is that they are not very accurate, compared to thermocouples or resistance thermometers. Moreover, thermistors are extremely non-linear. They are especially non-linear at high temperatures, so it is best to use them for measurements of less than 100°C. Finally, they need an excitation current, more commonly known as a voltage source.
What causes a thermistor to go bad?
The main cause of a failure of a thermistor is an open circuit. This may be due to mechanical separation between the resistor element and the lead material, caused by handling damage, excessive heat, thermal mismatch and more.
How to check the thermistor using a multimeter?
In order to check a thermistor using a multimeter, you need to put the multimeter into resistance and connect either side of the thermistor. Heat the thermistor with something like a hot air gun.
A properly functioning positive temperature coefficient thermistor will show a smooth and steady increase in the multimeter resistance reading. A properly functioning negative temperature coefficient thermistor will show a smooth and steady decrease in the multimeter resistance reading.
Look for signs of a faulty thermistor. A steady reading that does not change, a reading of zero or reading of infinity are all indications that the thermistor needs to be replaced. The change in reading will not be smooth or there will not be any change.
Conclusion
A thermistor is a variable resistor, which resistance is dependent on temperature, comparing it to the standard resistors. There are two types of thermistors, a “Negative Temperature Coefficient (NTC)” which has less resistance at higher temperatures and a ‘’Positive Temperature Coefficient (PTC)”. They have more resistance at higher temperatures. Thermistors are used in household appliances and many more cases due to their versatility based on their numerous advantages.
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