Oxides of the metals are used for the creation of the thermistors. During their manufacturing, the ratio of the resistance and temperature is defined accuratly because it is an important factor that defines the function of the thermistor. In today’s post, we will have a look at working, manufacturing, and other different related parameters. So let’s get started with What is Thermistor.
What is Thermistor
- A thermistor is a resistor whose value of the resistance alters with the change of the temperature.
- The word thermistor is a combination of the two words first is thermal that means heat and second is resistance.
- In electrical circuits, the thermistors are used to stop the inrush current from the circuitries, as they are also sensors with the variation of the resistance they indicate about current.
- There are the 2 main categories of the thermistors first one is the NTC (negative temperature coefficient) and second is PTC (positive temperature coefficient).
- Negative temperature coefficient thermistor is such resistor whose resistance value falls with the increment of the temperature.
- NTC (Negative temperature coefficient) thermistors are mostly used for the resistance computations and to limit the value of the current in different circuitries.
- The positive temperature coefficients are such thermistors whose resistance value increases with the increment in the temperature.
- The PTC used in circuitries to provide protection against the overcurrent in the circuitries.
- These resistors are formed by crushing the oxides of the different metals using different methods for their creation.
- The main difference among the RTD (resistance temperature detector) and the thermistor is that RTD is manufactured by different metals while thermistors are formed by ceramic substances.
Working of Thermistor
- The resistance of the thermistor varies with the variation in the temperature. For calculation of the thermistor’s resistance ohm-meter can be used.
- If we can find the accurate variation in the resistance of the thermistor with the variation in the temperature than we can easily find the value temperature by the resistance value.
- The material used for the creation of the thermistor defines how much variation will occur in the resistance.
- If we draw graphical representation among the resistance and the temperature than we will get the non-linear curve. It is shown in the given figure.
Construction of Thermistor
- For the production of the thermistor powder form of the 2 or more than the two oxides of metals blend to form paste-like arrangments.
- Then the different wires are inserted into this paste of metallic-oxides for the circuit connection, after that this composition is put into the oven for the removal of the water and to make it solid.
- After drying the paste solid obtained from the oven will be covered with the glass coating to provide protection from the moistures.
- In market numerous types, configurations and size of the thermistors are available.
- The smaller size thermistors have dia of 0.15 to 1.5 mm and their shape is similar to grains.
- These resistors are also available in the ring-like arrangements that formed during moulding of the thermistor that has dia of three mm to twenty-five mm.
- The resistance values that are used in a thermistor is one kilo-ohm, two kilo-ohms, ten kilo-ohms, etc.
Types of Thermistors
- There are two main types of the thermistors first one is the NTC (Negative Temperature Coefficient ) and the second one is PTC (Positive Temperature Coefficient).
- Let’s discuss them with the detailed.
- This kind of thermistors is constructed by pressing the disc made by different semiconductors.
- When the temperature of these thermistors increases, the energy of the electrons of the material also increases, then they start to flow in the structure of the thermistor.
- The current due to movements of these electrons can be described in a given formula.
I = (n.A.v.e)
- In the above-given equation the ‘I’ is the current.
- ‘n’ is the no of the electrons.
- A is the area of the thermistor.
- ‘v’ is the speed of the electrons.
- ‘e’ is a charge of the electrons, its value is 1.602 10^-19.
- The current produced by the movement of the electrons can be found by the ammeter.
- In this thermistors, the increment in the value temperature also increases the resistance and decrement in temperature will decrease the resistance.
- As NTC (Negative Temperature Coefficient) thermistors are commonly used but PTC is used for special circuitry like to provide protection. It also works as the replacement of the fuses.
- The operating temperature range for this thermistor is among the sixty Celcius and one twenty-degree Celcius.
- In special-cases its operating temperature can be zero to two hundred Celcius.
Comparison between Thermistor and Thermocouple
- Now we describe the differences between the thermistor and thermocouple with detailed.
- The temperature measurement range for the thermistor is fifty-five celsius to plus one fifty-five celsius.
- It used for the measurement of the temperature.
- The thermistor shows the non- linear behaviour for the resistance and the temperature.
- In the case of the NTC (Negative Temperature Coefficient) the increment of the temperature will decrease the resistance.
- It can very easily assemble in the circuitries there is no need of special modification for the thermistor.
- The operating range for the thermocouple is from minus two hundred to minus three-fifty for ‘T’ category, ‘J’ category temperature is ninety-five to seven sixty celsius, category ‘k’ has a temperature range from ninety-five to twelve sixty celsius.
- Its accuracy is higher.
- Its working principle is that it finds the value of the different at its terminals then find temperature using these voltages.
Applications of Thermistor
- These are some applications of the thermistors.
- The thermistor used for the calculations of the higher frequency energy signals.
- The thermal conductivity of the different substance can be found by the thermistor.
- It also used to calculate the composition of different gases.
- The pressure of the liquids can be calculated by the thermistors.
It is the detailed article on the thermistor if you have any question ask comments. Thanks for reading. Take care until the next tutorial.