UNIT IV OPTICAL, PRESSURE AND TEMPERATURE SENSORS
PART A
1. Mention the materials used for thermistors.
Mixture of metallic oxides such as manganese, nickel, cobalt, copper, iron and
uranium.
2. What are the applications of thermistors?
1. Measurement of power at high frequencies
2. Measurement of thermal conductivity
3. Measurement of level, flow and pressure of liquids
4. Measurement of composition of gases
5. Vacuum measurements
6. Providing time delay.
3. What are the advantages and disadvantages of resistance thermometers?
Advantages:
● They are suitable for measuring large temperature differences and high
temperatures.
● Well designed resistance thermometers have excellent stability.
● Unlike thermocouples, they do not need a reference junction and this
favors them in many aerospace and some industrial applications
Disadvantages:
● The resistance element is usually more expensive than a thermocouple.
● They need auxiliary apparatus and power supply.
● There are errors due to self heating and thermoelectric effect of the
resistive element and connecting leads.
4. Mention the features of thermistors.
o Compact, rugged and inexpensive
o Good stability
o The response time of thermistors can vary from a fraction of a
second to minutes.
o Self-heating of thermistors is avoided.
o Thermistors can be installed at a distance from their associated
measuring circuits.
5. What are nanosensors?
Nano-sensors are nanoscale devices that measure physical quantities and
convert those quantities to signals that can be detected and analyzed
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6. List out the development of Nano-sensors.
Integration of nanoparticles into gas sensors.
Implantation of biological motors into non biological environments.
Development of chemical synthetic methods to realize nanocrystals
7. List ten properties possessed by smart sensors (5m)
Automatic ranging and calibration through a built in digital system.
Auto-acquisition and storage of calibration constants in local memory of
the field device.
Auto configuration and verification of hardware for correct operation
following internal checks
Auto correction of offsets, time and temperature drifts.
Self tuning control algorithm
Auto linearization of non linear transfer characteristics
Control programme may be locally stored
Control is implementable through signal bus and a host system.
Conditional monitoring is also used for fault diagnosis.
Communication through a serial bus.
8. Explain the principle of piezoelectric transducer. List out the materials for
piezoelectric transducers. (4m)
● Quartz
● Rochelle salt
● Ammonium Dihydrogen Phosphate (ADP)
● Ceramics made with barium titanate, dipotassium tartrate & lithium sulfate
9. What is tactile sensor
Tactile sensors are used to measure contact forces and to characterize
surface profiles and roughness.
10. List the types of radiation sensors
Photoelectric cell such as photoemissive cell.
Photoemf cell such as photovoltaic cell
Photoconductive cell such as light sensitive resistors.
Xrays and nuclear radiation detection such as Geiger-Muller counter.
11. What is the difference between thermistor and RTD?
Sensor type Thermistor RTD
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Temperature range -100 to 325o C -200-650oC
Linearity Exponential Linear
Response time Fast Slow
Cost Low to moderate High
12. List the materials used in RTD.
Nickel, Copper & Platinum
13. What is negative temperature coefficient thermistor? List few of its
applications(4m)
A negative coefficient for a material means that its resistance decreases with an
increase in temperature.
Automotive applications
Food handling and Processing industry
Very low resistance thermometer
14. State the thermoelectric law.
Law of intermediate temperature: The emf for a couple, each element of which
is homogeneous in constitution, with junction at temperatures T1 and T2 is not
affected by temperatures elsewhere in the circuit.
Law of intermediate metals: If a third homogeneous metal is inserted anywhere
in the couple without affecting the junctions J1 and J2 and their temperatures T1
and T2, and the new junctions of the inserted metal having identical temperature,
the thermocouple remains unaffected.
Law of homogeneous circuit: If the circuit is made of a single homogeneous
metal, no current flows through the applications of heat alone and no
thermocouple develops.
15. List six commonly used techniques for producing thin film sensors.
A number of techniques are used for thin film deposition, such as
● Thermal evaporation
○ Resistive heating
○ Electron beam heating
● Sputter deposition
● Chemical vapour deposition
● Plasma enhanced chemical vapour deposition
● Metallo organic deposition -
16. Define Smart Sensor
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A smart sensor is a system-in-package in which a sensor and dedicated interface
electronics are realized.
17. List out the advantages of MEMS
Microminiature size and weight
Large surface-area-to-volume ratio (when compared in the same
measurement
units)
Large-scale integration (LSI) of components/circuits
High performance
High speed (20 ns switching speeds)
Low power consumption
Easy mass production
Low cost (in mass production)
18. What is meant by self–heating error in a resistance thermometer?
Resistance thermometers need to have a current passing through them which is
likely to cause an error often termed as the self heating error. The heat,
produced in the sensor because of this current flows towards the zone whose
temperature is to be measured through the surrounding walls and sheaths and
.
19. Enumerate the applications of MEMS
Automotive (e.g., accelerometers and gyroscopes or IMUs for airbag
deployment, handling control, safety and collision avoidance, ride quality, and
dynamic stability, brakes, car tire pressure sensors)
Biomedical applications ( micro disposable blood pressure sensors,
sensors for intraocular pressure in eyes, microphone and hearing aids)
Computers, consumer electronics, and home appliances (touch screen
controllers;inkjet printer nozzles and cartridges; IMUs and microphones for
cell phones, laptops, tablets, game controllers, personal media players, digital
cameras)
Optical MEMS (micromirrors, scanners, picoprojectors, fog-free lenses, light
sensors for IR imaging)
20. What are called MEMS?
MEMS are microminiature devices consisting of microelectronic components
such as sensors, actuators, and signal processing integrated and embedded into
a single chip while exploiting both their electrical/electronic and their mechanical
features sense variables like force, pressure, temperature, acceleration and
displacement.
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21. Draw the resistivity versus temperature characteristics of thermistor
22. Draw the symbol of photoresistor and list out its applications
good infra-red detector
alarm devices, solar street lamps,
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