Sensors & Transducers: Sensors and Transducers-II Unit 2 Part 1

Que2.1. Explain the construction and characteristics of  thermistor. 

Answer  Thermistor 

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

2. Although all resistors ’ resistance will change slightly with temperature,  a thermistor is particularly sensitive to temperature changes. 

3. Thermistors follow the principle of  drop in resistance with  adding   temperature. 

4. The material used in thermistor is generally a semiconductor material   similar as a sintered essence oxide(  fusions of essence oxides, chromium,  cobalt, iron, manganese and nickel) or  unravel polycrystalline ceramic  containing barium titanate( BaTiO3) and other  composites. 

5. As the temperature of semiconductor material increases the number of  electrons  suitable to move about increases which results in  further current in  the material and reduced resistance. 

6. Thermistors are rugged and small in  confines. They  parade nonlinear  response characteristics. 

7. Thermistors are available in the form of a blob( pressed slice),  inquiry or . It has a small blob of dimension from0.5 mm to 5 mm  carpeted with  ceramic or glass material. 

9. The blob is connected to an electric circuit through two leads. To  cover  from the  terrain, the leads are contained in a  pristine  sword tube.  Thermistor characteristics 

1. The relationship between temperature and resistance is given as  where, R1 =  Resistance of the thermistor at absolute  temperature T1( K).  R2 =  Resistance of the thermistor at temperature  T2( K).  =  Constant depending upon the material of the  transducer. 

2. As we can see in the eq.(2.1.1) the relationship between temperature  and resistance is  largely nonlinear.  3. A standard NTC thermistor  generally exhibits a negative thermal resistance  temperature measure of about0.05/ °C.  

Que2.2. bandy the working principle of thermistor. 

Answer  Working principle 

1. The working principle of a thermistor is that its resistance is dependent  on its temperature. We can measure the resistance of a thermistor  using an ohmmeter. 

2. As we’ve relationship between the temperature and the resistance of  the thermistor by measuring the thermistor’s resistance we can  decide  its temperature. 

3. Change in resistance depends on the type of material used in the  thermistor. 

4. The relationship between a thermistor’s temperature and resistance is non-linear. A typical thermistor graph is shown inFig.2.2.1.  Applications of thermistors 

1. To cover the coolant temperature and/ or  oil painting temperature inside the  machine. 

2. To cover the temperature of an incubator. 

3. Thermistors are used in  ultramodern digital thermostats. 

4. To cover the temperature of battery packs while charging. 

5. To cover temperature of hot ends of 3D printers. 

6. To maintain correct temperature in the food  running and processing  assiduity accoutrements . 

7. To control the operations of consumer appliances  similar as broilers,  coffeemakers, refrigerators, freezers, hair dryers,etc.   

Que2.3. Describe the construction and working of thermocouple. 

Answer  Principle 

1. The  introductory principle of thermocouple is grounded on a law called Seebeck  effect. 

2. Seebeck effect states that when two different essence are in contact, a  implicit difference or a voltage is generated. That voltage is a function  of temperature. 

3. The device with two different essence is called thermocouple and the  voltage is known as Seebeck voltage. It’s  substantially used for  dimension  of temperature. 


1. For the construction of thermocouple, a brace of two different essence is  welded together at the junction point to form a thermocouple. 

2. The junction J1 and junction J2 must be at different temperature.  Working  1. InFig.2.3.1, when heat is applied to any one junction J1 or J2, of two  different essence an emf or voltage is produced which is to be measured  at the another junction. 

2. These two different essence make an electric circuit, due to this  implicit difference, and a voltage is generated in the circuit. 

3. Hence, a current( I) flows in the circuit. This current overflows in the circuit  as long as T1> T2. The T1 and T2 are the temperatures at the junctions. 

4. The voltage produced is a function of difference in temperature of the  two junctions J1 and J2 and is given by,   

Que2.4. Explain the operation of RTD( Resistance Temperature  Sensor). 

Answer  Operation 

1. A resistance thermometer or resistance temperature sensor is a device  which used to determine the temperature by measuring the resistance  of pure electrical  line. 

2. This  line is appertained to as a temperature detector. If we want to measure  temperature with high  delicacy, RTD is the only one  result in   diligence. 

3. It has good direct characteristics over a wide range of temperature. 

4. They’re grounded on semiconductors which  bear as a resistor. Semiconductor  has negative temperatureco-efficient. 

5. When a temperature is applied on it, the resistance of device decreases  with increase in temperature. 

6. This  diminishment in resistance is equally commensurable to temperature. 

7. Relation between resistance and temperature is given as.   

Que2.8. What’s thermal imaging? 

Answer  1. Thermal imaging is a  system of  perfecting visibility of objects in a dark   terrain by detecting the object’s infrared radiation and creating an  image grounded on that information. 

2. Thermal imaging, near- infrared illumination, low- light imaging and are  the three most generally used night vision technologies. 

3. Thermal imaging works in  surroundings without any ambient light.  Thermal imaging can access obscurants  similar as bank, fog and  haze.   

Que2.9. How thermal imaging  workshop? 

Answer  1. All objects emit infrared energy( heat) as a function of their temperature.  The infrared energy emitted by an object is known as its heat  hand. 

2. In general, the hotter an object is, the  further radiation it emits. A thermal  imager( also known as a thermal camera) is basically a heat detector  that is able of detecting  bitsy differences in temperature. 

3. The device collects the infrared radiation from objects in the scene and  creates an electronic image grounded on information about the temperature  differences. 

4. Because objects are infrequently precisely the same temperature as other  objects around them, a thermal camera can  descry them and they will  appear as distinct in a thermal image. 

5. Thermal cameras more or less record the temperature of  colorful objects  in the frame, and  also assign each temperature a shade of a colour,  which lets you see how  important heat its radiating compared to objects  around it. 

6. Thermal images are  typically grayscale in nature black objects are  cold, white objects are hot and the depth of argentine indicates variations  between the two. 

7. Some thermal cameras,  still, add color to images to help  druggies  identify objects at different temperatures. 

8. There are two common types of thermal- imaging  bias Un-cooled 

i. This is the most common type of thermal- imaging device. The infrareddetector   rudiments are contained in a unit that operates at room  temperature. 

ii. This type of system is  fully quiet, activates  incontinently and has  the battery  erected right in. 

Cryogenically cooled .

i. More  precious and more susceptible to damage from rugged use, these  systems have the  rudiments sealed inside a  vessel that cools them to  below 32 F( zero °C). 

ii. The advantage of such a system is the  inconceivable resolution and  perceptivity  that affect from cooling the  rudiments.  iii. Cryogenically- cooled systems can “ see ” a difference as small as  F(0.1 °C) from  further than,000 ft( 300 m) down.

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