Temperature is something that people measure a lot. This is done with the help of devices called temperature sensors. There are many different types of temperature sensors which are either constructed and work in a different way than the rest or are made from different materials. Therefore, some temperature sensors are suitable for certain types of applications, while others are suitable for a completely different type of applications.
The wide variety often makes it difficult for people to make the right choice, but all that needs to be considered is the way a temperature sensor works and what it is going to be used for. Some of the most commonly used temperature sensors are thermocouples, thermistors and resistance temperature detectors. Each one of those has its own set of benefits, but in this article we are going to mainly talk about thermistors.
Introduction to thermistors
Thermistors are actually very similar to RTDs (resistance temperature detectors) in the way they change resistance when temperature changes. However, unlike RTDs, thermistors offer much higher sensitivity and this means that the resistance of a thermistor will change significantly more when responding to the changes in temperature.
The majority of thermistors actually have a negative temperature coefficient which means that when the temperature increase their resistance decreases. Another thing that should be noted is that thermistors are less linear than resistance temperature detectors and for that reason they require a correction factor.
Pros and cons
There are certain advantages that thermistors have over other types of temperature sensors. One of those advantages is that they are extremely easy to use and set up. Thermistors can be operated with the very standard two wire measurement method. The response time of this type of temperature sensors is also very fast. Some thermistors are very small which allows them to quickly respond to temperature changes.
One of the drawbacks of using thermistors is that they have non-linear properties and therefore require linearization. Their temperature range is quite limited and they are not as durable as RTDs or thermocouples for example. The fact that thermistors are semiconductors means that de-calibration problems at high temperature are more likely to occur. Also, thermistors have self-heating characteristics just like RTDs.
There are some common mistakes that people make when using thermistors. One of these mistakes is to not allow for self-heating and actually selecting a device that doesn't have an adequate temperature range. Fortunately, there are several things that can be done in order to reduce the self-heating effects to a certain extent. One of those things is to use a pulsed DC current instead of a constant one.
There are also other things that can go wrong with a thermistor, but most of these are due to human error. Thermistors are great temperature sensors and they can be used in many different applications just like thermocouples and RTDs. Keep this type of sensors in mind next time when you have to select one for your project.