Thermistors are very important in a circuit, and no one can deny their importance in various circuits. They act like passive components in an electric circuit. Thermistors are cheap, durable, and easy to use in the system. You can find their use in everyday items such as digital thermometers and household appliances etc.

What is a Thermistor?

A Thermistor is a semiconductor type of resistor. The electrical resistance is dependant on temperature. The word ‘Thermistor’ is a combination of thermal and resistance.  Thermistors are super sensitive to temperature. That’s why their resistance varies with a slight change in temperature. When there is a change in the temperature, there will be a measurable change in the resistance of the thermistor.

They are composed of metallic oxide, which is molded into beads, disks, or cylindrical shapes. The epoxy or glass encloses them and further gives them waterproof properties. They do not work well in extremely hot or cold temperatures. They are precise when they are for a limited temperature range of about 50 degrees around the target temperature. The base resistance will show the range of the resistance.

Working Procedure of Thermistor in a Circuit.

A thermistor works in such a way that its resistance is reliant on its temperature. If we know the relationship between how the temperature change will affect its resistance, then by measuring the resistance, we can derive its temperature. At the same time, the resistance changes depending on the material used in thermistors. The relationship between the resistance of a thermistor and its temperature is non-linear. You can use an ohmmeter to find out the resistance of the circuit.

Types of Thermistors

Depending on the working procedure, there are two types of thermistors.

• Negative Temperature Coefficient (NTC) Thermistor
• Positive Temperature Coefficient (PTC) thermistor

Negative Temperature Coefficient (NTC) Thermistor

NTC thermistors have the abundant uses in our life. The resistance of the NTC thermistor is inversely proportional to its temperature. NTC’s resistance decreases with the increase in temperature; usually, due to an increase in induction, the electrons are bumped up by thermal agitation from the valence band and vice versa. You can find them in temperature sensors or as inrush current limiters.

Positive Temperature Coefficient (PTC) Thermistor

PTC (positive temperature coefficient) thermistor is not as common as NTC. However, engineers use it as a fuse for the protection of circuits. PTC acts as a current limiting device.

When the temperature increases, its resistance also increases, usually due to increased thermal lattice agitations of impurities and imperfections. While the resistance of PTC decreases with the decrease in temperature.

Advantages of Thermistor

Thermistors have the following advantages:

• They are durable. It means you can use thermistors for a longer period of time.
• They are relatively affordable. On the other hand, other temperature sensors like thermocouples or RTDs are expensive and not readily available.
• These are compact and easy to use. You can easily use them in the circuit. Additionally, their small size makes them ideal for circuits where space is a major concern.
• Thermistors work in a wide range of temperatures. Therefore, they are perfect in high-temperature conditions as well.
• Have low power? Thermistors got your back. Thermistor circuits can work even at very low power. So, when power consumption is your concern, use these thermistors.

The disadvantages of Thermistor Circuit

   Thermistors also have disadvantages such as:

• Curved output.

Applications of Positive Temperature Coefficient (NTC) Thermistor

• PTC thermistors are an integral part of many current-limiting devices for circuit protection as replacements for fuses. In this case, the thermistor’s resistance is relatively low at room temperature.
• You can use them as timers in the degaussing coil circuit of most CRT displays. A degaussing coil circuit using a PTC thermistor is reliable, cheap, and durable.
• With these types of thermistors, you can measure the level of liquid in the tank. As the level of the liquid rises, the temperature changes, which it can detect easily.
• Engineers use these transistors in temperature-compensated synthesizer voltage-controlled oscillators.
• This type of thermistor is helpful where there is a need to sense the temperature. For example, in motors, they can sense the temperature when it is overheating and limit the current accordingly.
• PTC thermistors are useful in heaters in automotive industries to provide additional heat inside the cabin with a diesel engine or to heat diesel in cold climate conditions before engine injection.

Applications of Negative Temperature Coefficient (NTC) Thermistor

• You can use NTC thermistors as thermometers for low-temperature measurements of about 10K.
• Engineers use them as inrush current limiter devices in power supply circuits.
• As sensors in automotive applications to monitor fluid temperatures such as cabin air, engine coolant, external air, or engine oil temperature.
• They are important to monitor the temperature of an incubator. As you know, temperature maintenance is crucial in such systems.
• You can find them in household appliances for measuring temperatures, like coffee makers, ovens, refrigerators, freezers, toasters, hair dryers, etc.
• Temperature is a critical factor in many industries. NTC thermistors have a number of applications in the food handling and processing industry.

To Conclude…

Thermistors are temperature-dependent resisters. Their resistance varies with the change in temperature as they react to a minor change in temperature. They are ideal when used for a specific temperature that you want to maintain in a system.

Thermistors offer the best way to measure and control the temperature of a thermo-electric cooler as part of a temperature control system due to their capability to adjust in slight increments. They can be embedded or surface-attached to the device to be monitored, as they provide better results when they are close to the devices.

Thermistors come in a wide range. They are of two types depending on their working procedure. You can find them in a variety of different shapes. They are made up of metallic oxides, which are enclosed with impermeable materials like glass or epoxy. So, that’s it with the thermistor circuit. We have articulated everything you should know about the types and applications of a thermistor circuit.