Thermistor MCQ Quiz in मल्याळम - Objective Question with Answer for Thermistor - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Thermistor:

• It is a kind of resistor whose resistivity depends on the surrounding temperature.
  It is a temperature-sensitive device.
• The word thermistor is derived from the word, thermally sensitive resistor.
• The thermistor is made of semiconductor material that means its resistance lies between the conductor and the insulator.
• The variation in the thermistor resistance shows that either conduction or power dissipation occurs in the thermistor.

The thermistor is classified into types.

• Negative Temperature Coefficient (NTC) Thermistor –
  • In this type of thermistor, the temperature increases with the decrease of the resistance or resistance decrease with increasing temperature.
  • The resistance of the negative temperature coefficient thermistor is very large due to which it detects the small variation in temperature.
• Positive Temperature Coefficient (PTC) Thermistor –
  • The resistance of the thermistor increases with the increases in temperature.

Concept:

We Know the Thermistor Equation:

Where,

T₁ and T₂ are the temperatures in Kelvin.

 R1 and R2 are Thermistor resistance at T1 and T2 respectively.

Given:

We have,

T₁ = 25 +273.15 = 298.15

T2 = 100 +273.15 = 373.15

R₁ = 10 kΩ

 β_(T1/T2) = 3455

Calculation:

Now, to calculate the value of resistance (R₂)-

\(\begin{aligned} &3455=\frac{111254.6725}{75} \times \ln \left(\frac{10000}{R_{2}}\right) \\ &3455=1483.4 \times \ln \left(\frac{10000}{R_{2}}\right) \\ &e^{\left[\frac{3455}{1483.4}\right]}=\frac{10000}{R_{2}} \\ &\therefore R_{2}=\frac{10000}{e^{2.33}}=973 ~\Omega \end{aligned}\)

So, the value of resistance is 973 Ω.

The thermistor is temperature-dependent. It is a nonlinear resistance thermometer. It is a highly sensitive element.

\({R_{T1}} = {R_{T0}}{e^{\beta \left( {\frac{1}{{{T_1}}} - \frac{1}{{{T_0}}}} \right)}}\)

R_T1 is the resistance at temperature T₁,

R_T0 is the resistance at temperature T₀, β = temperature constant

As the temperature increases, there are many bond breaks and more electrons/holes that contributor to the conduction therefore resistance of the thermistor decreases (producing a negative temperature coefficient). By this process, we can measure temperature.

• Thermistors are generally made up of semiconductor materials.
• Thermistors have a negative temperature coefficient of resistance i.e. the resistance decreases with an increase in the temperature.
• Thermistors can measure the temperature in the range of -100°C to 300°C.

The basic circuit used for this purpose is shown below:

Advantages of thermistor:

• It is rugged and compact.
• It is inexpensive.
• It has good stability.
• It requires relatively simple circuitry.
• The response time of a thermistor can vary from a fraction of second to minutes, depending on the size of the detecting mass and capacity of the thermistor. 

At 25°C, R_eq = 1500 + R_o

At 50°C, R_eq = 1500 [1 + (-0.02) 25] + R_o [1 + (0.005) (25]

1500 + R_o = 1500 [1 – 0.5] + R_o [1 + 0.0125]

⇒ 1500 + R_o = 750 + 1.125 R_o

\(\Rightarrow {R_o} = \frac{{750}}{{0.125}} = 6\;k{\rm{\Omega }}\)

A thermistor (or thermal resistor) is defined as a type of resistor whose electrical resistance varies with changes in temperature.

Thermistors have a variety of applications. They are widely used as a way to measure temperature as a thermistor thermometer in many different liquid and ambient air environments.

• Digital thermometers (thermostats)
• Automotive applications (to measure oil and coolant temperatures in cars & trucks)
• Household appliances (like microwaves, fridges, and ovens)
• Circuit protection (i.e. surge protection)
• Rechargeable batteries (ensure the correct battery temperature is maintained)
• To measure the thermal conductivity of electrical materials
• To measure the percent of CO₂ in air
• Temperature compensation (i.e. maintain resistance to compensate for effects caused by changes in temperature in another part of the circuit)
• Used in Wheatstone bridge circuits

R_T = 3 kΩ at 25°C

At 30°C, R_T = 3 kΩ – 5(150) = 2.25 kΩ

Now, the circuit becomes

By virtual ground, V_A = V_B

⇒ V_A = 0 V

By KCL at V_A,

\(\frac{{{V_A} + 1}}{1} + \frac{{{V_A} - {V_{out}}}}{{2.25}} = 0\) 

\(\Rightarrow \frac{{0 + 1}}{1} + \frac{{0 - {V_{out}}}}{{2.25}} = 0\) 

⇒ V_out = 2.25 V

At 30°C, R_th = 5 kΩ

\({V_D} = \frac{{{R_{th}}}}{{{R_{th}} + 5\;k{\rm{\Omega }}}} \times 10\;V = 5\;V\) 

Power dissipated in thermistor, \(D = \frac{{{V^2}}}{{{R_{th}}}} = \frac{{{{\left( 5 \right)}^2}}}{{5 \times {{10}^3}}} = 5\;mW\)

\({\rm{\Delta }}T = \frac{P}{{{P_D}}} = \frac{{5\;mW}}{{5\frac{{mW}}{{^\circ C}}}} = 1^\circ C\) 

\({R_{th}} = 5\;k{\rm{\Omega }} + \left[ {1^\circ C \times \frac{{ - 10}}{{100}} \times 5\;k{\rm{\Omega }}} \right] = 4.5\;k{\rm{\Omega }}\) 

Explanation:

Thermistors for Temperature Measurement

Definition: A thermistor is a type of temperature-sensitive resistor that exhibits a significant change in resistance with a change in temperature. It is widely used for temperature measurement, control, and compensation in various applications due to its high sensitivity and precision.

Correct Option Analysis:

The correct answer is:

Option 2: Negative temperature coefficient

This option correctly describes the behavior of commonly used thermistors for temperature measurement. Negative Temperature Coefficient (NTC) thermistors are characterized by a decrease in resistance as the temperature increases. This property makes them ideal for precise temperature measurement applications.

Working Principle:

NTC thermistors operate based on the principle that their resistive material exhibits a negative temperature coefficient. As the temperature rises, the thermistor's resistance decreases exponentially. This behavior occurs due to the increase in the number of charge carriers (electrons and holes) available in the material, which enhances conductivity. The relationship between resistance (R) and temperature (T) is often expressed mathematically as:

R(T) = R₀ × e^(β/T)

Where:

• R₀: Resistance at a reference temperature
• β: Material constant
• T: Temperature in Kelvin

Advantages of NTC Thermistors:

• High sensitivity to temperature changes, making them suitable for precise measurements.
• Compact size and ease of integration into electronic circuits.
• Cost-effective solution for temperature sensing and monitoring.
• Wide range of operating temperatures, enabling diverse applications.

Applications:

• Temperature measurement in electronic devices, such as thermostats and temperature sensors.
• Overcurrent protection in circuits by monitoring temperature rise.
• Compensation for temperature-induced variations in electronic components.
• Used in automotive, medical, and industrial equipment for temperature control.

Explanation:

Thermistors are temperature-sensitive resistors whose resistance changes with temperature variations. There are two types of thermistors: Negative Temperature Coefficient (NTC) thermistors, where resistance decreases as temperature increases, and Positive Temperature Coefficient (PTC) thermistors, where resistance increases as temperature increases. In most practical applications, NTC thermistors are commonly used.

In the provided statement, we are dealing with the change in resistance of a thermistor with respect to the surrounding temperature. Here's a detailed explanation of the correct option:

The correct option is: Option 2: decrease; increase

This means that if the temperature of the surrounding medium increases, it will result in a decrease in the resistance of the thermistor and an increase in the current. This is characteristic of an NTC thermistor. As the temperature rises, the resistance of the NTC thermistor drops, which allows more current to pass through the circuit, thus increasing the current.

Understanding NTC Thermistors:

• NTC thermistors are made from semiconductor materials. When the temperature increases, the number of charge carriers in the thermistor increases, which reduces the resistance.
• The relationship between temperature and resistance in NTC thermistors can be approximated by the Steinhart-Hart equation, which is a more accurate model for thermistors over a wider temperature range.
• In practical applications, NTC thermistors are used in temperature sensing, temperature compensation, and inrush current limiting.

Let's dive deeper into the physics behind NTC thermistors:

Physics of NTC Thermistors:

• NTC thermistors are typically composed of ceramic materials made from mixtures of metal oxides such as manganese, nickel, cobalt, copper, and iron.
• As temperature increases, the thermal energy provided to the thermistor's semiconductor material excites more electrons into the conduction band, which results in increased electrical conductivity (i.e., decreased resistance).
• The decrease in resistance with increasing temperature follows an exponential relationship, which is why NTC thermistors are highly sensitive to small changes in temperature.