What Is a Thermistor Thermometer?
Thermistor thermometers use thermistors to measure temperature. A thermistor is a semiconductor device with an electrical resistance that is proportional to temperature. The name is formed from a combination of the words "resistor" and "thermal."
Significance
All conductors have an electrical resistance proportional to their temperature. Everyday devices such as toasters, heaters and light bulbs operate on this principle. Thermistors are created to deliberately optimize this property, and are more temperature-sensitive than regular resistors. This sensitivity makes them able to do thermal measurements to within ranges of +/- 0.02 percent to +/- 0.05 percent, an accuracy which makes them very effective thermometers.
Types
There are two types of thermistors. They are PTC, which stands for Positive Temperature Coefficient of Resistance, and NTC, which stands for Negative Temperature Coefficient of Resistance.
NTCs are the most common types of thermistors. They have temperatures that vary inversely with their resistance, so that when the temperature increases, the resistance decreases; and when the temperature decreases, the resistance increases. Their other role is that of current suppressors.
PTC thermistors are the opposite of NTCs; when the temperature increases, so does the resistance, and when the temperature decreases, the resistance does likewise. In addition to being used as thermometers, they are also used as switches, and for circuit overload protection.
Construction
NTCs are made from oxides of materials such as nickel, manganese, copper, iron and cobalt. Some are also made from silicon, germanium or a combination of both. PTCs are constructed using semiconductors combined with ceramics or polymers.
Uses
In medicine, thermistors are used as clinical temperature sensors, in stethoscopes and as probes during surgery. They are found in other medical devices where temperature detection and control is vital. Since they regulate temperature and provide protection against overheating in circuits, they can be found in cars, cell phones, computers, amplifiers, home appliances and more.
Expert Insight
Thermistors make superior thermometers because they are small, very stable, are long lasting and are very accurate. This makes them better at measuring temperature than thermocouples. The disadvantage is that like typical semiconductors they are non-linear, and so circuits must be designed with this limitation in mind. Also, unlike thermocouples, they cannot be used at extreme temperatures, and so are usually limited to 0 degrees Celsius to 100 degrees Celsius.
Tags: when temperature, makes them, Coefficient Resistance, decreases resistance, degrees Celsius