NTC thermistor（Equipment） application
The first NTC thermistor was discovered by Michael Faraday in 1833 and he was given a report on the silver sulfide semiconducting behavior. He observed that the silver sulfide resistance is decreased dramatically once the temperature increased. Because initial thermistors were hard to create & the technology applications were partial and commercial thermistors production did not start until the 1930s.
So, a commercially viable thermistor namely “Duracell” was launched in 1930 by Samuel Ruben. After that, the investigation of NTC thermistors attains major development because of the development in incessant transistor technology. So finally NTC thermistors were developed in 1960. So this article discusses on NTC thermistors, working with applications.
What is NTC Thermistor?
In an NTC thermistor, the term NTC stands for “Negative Temperature Coefficient” is an electric resistor with a negative temperature coefficient which means the resistance will be reduced once the temperature increases. These are mainly used as current-limiting devices and resistive temperature sensors. The NTC thermistor symbol is shown below according to the IEC standard.
As compared to silistors or silicon temperature sensors, the temperature sensitivity coefficient of this thermistor is five times higher & ten times higher than RTDs (resistive temperature detectors). The materials used to make these Thermistors are; nickel, iron, copper, manganese, and cobalt. The temperature range of these resistors ranges from −55°C to +200 °C.
NTC Thermistor Working Principle
The working principle of the NTC thermistor is mainly dependent on the ambient temperature. Once the thermistor’s temperature enhances then its resistance will be decreased. For every 1-degree centigrade rise of temperature, 5% resistance will be decreased.
There are two factors that affect a material’s resistance to electrical flow: the number of free electrons in the material and the ease with which they can move through it. The latter is affected by the crystal structure of the material, which will have more or fewer “free-electron paths” for the current to flow through.
NTC thermistors are made from ceramics containing metal oxides, including Mn-Ni-Co oxide, Ni-Cr oxide and Cu-Ni oxide with additives. When these metals are combined with oxygen, they form bonds that limit the number of free-electron paths in the crystal structure, increasing resistance.
At higher temperatures, however, collisions between atoms cause the crystal structure to break down slightly, releasing some electrons and creating free-electron paths where they didn’t exist before. The more free-electron paths there are, the less resistance there is to electrical flow. That’s how NTC thermistors exhibit a drop in resistance as temperature increases.
NTC Thermistor Specifications:
The specifications of an NTC thermistor include the following.
- Resistance is 10K ± 1% at 25 degrees Centigrade.
- B-value is 3950 ± 1%.
- Its response time is very fast from 0.12 to 10s.
- Dissipation factor δth is approximately 7.5mW/K.
- The thermal cooling time constant is <= 20 Sec.
- Temperature ranges from -55 °C to +200 °C.
- Available terminals are two.
- Linearity is exponential.
- Its accuracy ranges from 0.05°C to 1.00°C.
- The maximum tolerance is up to ±1.5% at –40°C & 150°C.
- Its cost ranges from low to moderate.