Everything You Need to Know About The PTC Thermistor
A thermistor is a type of resistance thermometer or resistor that has functions which depend on temperature. It is a temperature-sensing element made up of a sintered semiconductor material. A thermistor is also a powerful tool that exhibits a huge change in resistance which is proportional to a small temperature change. Thermistors are of two types - positive temperature coefficient (PTC) and negative temperature coefficient (NTC) viations. In this blog, we will talk about positive temperature coefficient (PTC) thermistors in particular.
What Is a Positive Temperature Coefficient (PTC) Thermistor?
A PTC thermistor is a type of resistor that has a positive temperature coefficient. The relationship between resistance & temperature is also linear. With this property, any increase of temperature will simultaneously cause a proportional change in the thermistor.
How Does a PTC Thermistor Work?
The function of a PTC thermistor is highly dependent on the adjustments of resistance that are caused by a change in temperature. After a rise in temperature is seen, the resistance of the thermistor will increase. When the temperature is reduced, the resistance will decrease. Meaning, in PTC thermistors, the resistance and temperature are directly proportional to each other.
An important component of PTC thermistors is their use of doped polycrystalline ceramic, which includes barium titanate and other compounds. The key reason behind using these materials is their ability to increase resistance when specific critical temperature changes occur.
Where Are These Thermistors Used?
PTC thermistors have many applications, and they are often utilized for the measurement, detection, control, and regulation of temperature. Apart from measuring temperature, thermistors are also used to sense liquid levels. Additionally, they find use for eliminating the risk of overcurrents in electrical circuits. The power of PTC thermistors has also been utilized in motor winding protection, and certain motor manufacturers use these resistors as a device for limiting current in motors.
Pros and Cons of Using PTC Thermistors
There are many many benefits of using PTC thermistors as they are very powerful and strong. As they are fairly compact in size, they can work well in a limited space. Thermistors also respond to temperature changes quickly and are not as expensive as compared to other temperature sensors. The best part is that no calibration is required during installation if the thermistor has an accurate resistance-temperature curve.
After looking at their advantages, it is also important to know the cons of PTC thermistors. The range of temperature offered by PTC thermistors is limited, meaning you cannot use them in applications where the temperature range is high. These thermistors require shielding in power lines and are quite delicate as well. At maximum temperatures, the result of their readings is non-linear. As such, they can only be used below 100°C. The non-linear characteristic of PTC thermistors will often be an issue when measuring certain temperatures.
Types of PTC Thermistors
There are 3 main types of PTC thermistors – Polymeric, Ceramic Switching, and Silistor Silicon. Polymeric PTC thermistors, or PPTC thermistors, exhibit a non-linear PTC effect. They are thermally activated devices, and even the slightest fluctuation in the ambient temperature will have an impact on performance.
Ceramic switching PTC thermistors have a non-linear resistance-temperature curve. After this type of thermistor is excited, the resistance will initially decrease until the desired level of temperature is achieved. These thermistors are increasingly being used in PTC heaters, sensors, and for protecting devices from over current, in addition to extreme temperatures, temperature compensation, and time delays.
Silistor silicon PTC thermistors use silicon as their conducting material. These linear devices show considerable PTC resistance. Despite this, after the temperature crosses the limit of 150°C, it starts showing a negative temperature coefficient (NTC). Due to their linear nature and temperature compensation, silistor silicon PTC thermistors can be used as PTC temperature sensors.
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