Electrical and Electronics Engineering - Unit 4 Notes

Unit-4 –Transducers and Sensors

Basic Principles and Classification of Instruments

  • Electrical measuring instruments are classified based on:
    • Quantity measured (e.g., Voltmeter, Ammeter, Wattmeter, Energymeter, Ohmmeter).
    • Principles used for their working (e.g., Moving Iron type, Moving coil type, Dynamometer type, Induction type).
    • How the quantity is measured (e.g., Deflecting type, Integrating type, Recording type).
  • Torques associated with measuring instruments:
    • Deflecting Torque: Acts on the moving system to give the required deflection, proportional to the quantity being measured.
    • Opposing Torque: Opposes the deflecting torque; components include inertia torque, control torque, and damping torque.
      • Inertia Torque: Due to the inertia of the moving system.
      • Control Torque: Always present, increases with deflection, opposes deflecting torque, and brings the moving system back to its initial position. Produced using spring or gravity.
        • Spring control: Uses helical springs connected to the spindle of the moving system.
        • Gravity control: Uses adjustable small weights on the moving system.
      • Damping Torque: Produced only during instrument operation to ensure the moving system reaches its final deflected position quickly.
  • Types of Electrical measuring instruments:
    • MOVING COIL INSTRUMENTS
      • PERMANENT MAGNET TYPE
      • DYNAMOMETER TYPE
    • MOVING IRON INSTRUMENTS
      • ATTRACTION TYPE
      • REPULSION TYPE

MOVING COIL INSTRUMENTS

PERMANENT MAGNET MOVING COIL INSTRUMENT [PMMC]
  • Principle: A current-carrying coil placed in a magnetic field experiences a force that moves it away from the field. This movement measures current or voltage.
  • Construction:
    • Permanent magnet with pole pieces (N and S).
    • Soft iron core (C) in the form of a cylinder.
    • Rectangular coil (MC) of many turns wound on a former (AF) made of aluminum or copper.
    • Spindle (Sp) attached to the moving coil.
    • Helical springs (S) connected to the spindle for control torque.
    • Pointer (p) attached to the spindle to move over a calibrated scale.
  • Working: The magnetic field produced by the permanent magnet exerts an electromagnetic force on the moving coil, causing the spindle and pointer to deflect proportionally to the current or voltage.
  • Deflecting torque: Directly proportional to current or voltage, suitable for measuring direct current and DC voltage.
  • Control torque: Spring control.
  • Damping torque: Eddy current damping induced in the aluminum former when it moves and cuts the magnetic flux lines.
DYNAMOMETER TYPE MOVING COIL INSTRUMENT
  • Principle: Similar to PMMC, but without a permanent magnet. Both operating fields are produced by the current and/or voltage to be measured.
  • Construction:
    • Fixed coil (FC) made in two sections.
    • Moving coil (MC) placed in the space between the fixed coil sections, attached to a spindle with a pointer.
    • Helical springs attached to the spindle for control torque.
    • Piston attached to the spindle moving inside an air chamber.
  • Working: The fixed and moving coils carry currents, producing two magnetic fields. The electromagnetic force on the moving coil causes it to deflect proportionally.
  • Deflecting Torque:
    • As voltmeter: Coils in series, carry current proportional to voltage. Deflecting torque proportional to (voltage)^2, suitable for AC and DC voltages.
    • As ammeter: Coils in series, carry the current to be measured. Deflecting torque proportional to (current)^2, suitable for AC and DC.
    • As wattmeter: Fixed coils carry system current, moving coil carries current proportional to system voltage. Deflecting torque proportional to VI \cos \phi (power).
  • Control torque: Spring control.
  • Damping torque: Air damping.

MOVING IRON INSTRUMENTS

ATTRACTION TYPE
  • Principle: A soft iron piece gets magnetized when brought into a magnetic field produced by a coil carrying current. The iron piece is attracted towards the portion where the magnetic flux density is maximum.
  • Construction:
    • Working coil carrying current to be measured or proportional to the voltage.
    • Soft iron disc attached to the spindle.
    • Pointer attached to the spindle moving over a calibrated scale.
  • Working: The working coil produces a magnetic field, attracting the soft iron disc towards the center of the coil, causing the spindle and pointer to deflect proportionally.
  • Deflecting Torque: Proportional to the square of the current or voltage, suitable for DC or AC, scale is non-uniform.
  • Control torque: Spring or gravity.
  • Damping: Air friction damping.
REPULSION TYPE MOVING IRON INSTRUMENT
  • Principle: Two iron pieces kept close together in a magnetic field get magnetized to the same polarity, producing a repulsive force. If one piece is movable, the force acts on it and moves it.
  • Construction:
    • Working coil carrying current proportional to voltage or the current to be measured.
    • Two iron pieces - fixed and moving.
    • Moving iron connected to the spindle with a pointer moving over a calibrated scale.
  • Working: The operating coil carries current, producing a magnetic field that magnetizes both iron pieces similarly, creating a repulsive force on the moving iron, causing the spindle and pointer to deflect.
  • Deflecting Torque: Proportional to the square of the current or voltage, suitable for DC and AC.
  • Control torque: Spring or Gravity.
  • Damping: Pneumatic (air damping).
  • Note:
    • MC instruments are used for DC Quantities only.
    • MI instruments are used for both DC & AC Quantities.

Digital Multimeter (DMM)

  • A common laboratory instrument that combines a voltmeter, ammeter, and ohmmeter.
  • Measures AC or DC voltages, AC/DC current, and resistance with a digital display.
  • Provides accurate digital output.

Parts of a Digital Multimeter

  • Display: Illuminated screen, typically with four digits (first can be 0 or 1) and +/- indication, along with indicators like AC/DC, etc.
  • Selection Knob: Used to select the function and range of measurement.
  • Ports: Three or four ports, but only two are needed at a time.
    • Common: Negative (black) probe connection for all measurements.
    • VΩmA Port: Positive (red) probe connection for most measurements.
    • 10A Port: Used for measuring large currents.

Measurements using Digital Multimeter

  • AC Voltage Mode: Input voltage is attenuated, rectified (full-wave), filtered, and then converted to digital by an ADC for display.
  • Current Measurement:
    • DC Current Mode: Measures the voltage drop across an internal calibrated shunt using ADC.
    • AC Current Mode: Converts AC to DC and measures the drop across an internal calibrated shunt using ADC.
  • Resistance Mode: Measures the voltage across an externally connected resistor, resulting from a current flowing through it from a calibrated internal current source.

Special Functions

  • Continuity Tester: Tests continuity between two points, produces an audio tone.
  • Diode Tester: Tests resistance in a diode for forward and reverse bias.
  • Battery Tester: Tests 9V and 1.5V batteries.

Advantages

  • Very high accuracy.
  • High input impedance, ensures less loading effect.
  • Numeric display provides zero parallax error.

Disadvantages

  • Does not do well with measurement fluctuations.
  • More expensive than analog meters.
  • Can be difficult to find one for specific needs.

Digital Storage Oscilloscope (DSO)

  • Stores a digital waveform or a digital copy of the waveform, allowing for digital signal processing.
  • Maximum frequency measured depends on the sampling rate and the nature of the converter.
  • Traces are bright, highly defined, and displayed quickly.

Block Diagram

  • Consists of an amplifier, digitizer, memory, analyzer circuitry, waveform reconstruction, vertical plates, horizontal plates, cathode ray tube (CRT), horizontal amplifier, time base circuitry, trigger, and clock.
  • Amplifier amplifies the input signal.
  • Digitizer converts the analog signal to digital.
  • Memory stores the digitized signal.
  • Analyzer circuit processes the digital signal.
  • Waveform Reconstruction converts the digital signal back to analog.
  • CRT displays the waveform.
  • Time base circuitry generates a ramp signal.

DSO Operation Modes

  • Roll Mode: Displays fast varying signals.
  • Store Mode: Stores signals in memory.
  • Hold or Save Mode: Holds some part of the signal for some time and then stores it in memory.

Waveform Reconstruction

  • Linear Interpolation: Dots are joined by a straight line.
  • Sinusoidal Interpolation: Dots are joined by a sine wave.

Factors Affecting Maximum Frequency

  • Sampling Rate: Must be twice as fast as the highest frequency of the input signal (Nyquist theorem).
  • Converter: Uses expensive flash converters, shift register can be used to reduce cost.

Applications

  • Checks faulty components in circuits.
  • Used in the medical field.
  • Measures capacitor, inductance, time interval, frequency, and time period.
  • Observes transistors and diodes V-I characteristics.
  • Analyzes TV waveforms.
  • Used in video and audio recording equipment.
  • Used in designing and research fields.
  • Displays 3D figures or multiple waveforms for comparison.

Advantages

  • Portable.
  • Highest bandwidth.
  • Simple user interface.
  • High speed.

Disadvantages

  • Complex.
  • High cost.

Transducer

  • A device that converts energy from one form (electrical, mechanical, chemical, optical, or thermal) to another.
  • Electrical transducer: has electrical energy in input or output.

Classification

  • Active transducers (self-generating): Generate their own voltage or current.
  • Passive transducers (externally powered): Require external power source for energy conversion.

Comparison between active and passive transducer

Active TransducerPassive Transducer
Self-generating type transducer.Externally powered transducer.
Does not require any auxiliary power supply.Requires auxiliary (external) power supply.
Signal conversion is simpler.Signal conversion is more complicated.
Energy from the physical quantity.Power derived from external source.

Examples

  • Active transducers: Thermocouple, Piezoelectric transducer, Photovoltaic cell, Moving coil generator, Photoelectric cell
  • Passive transducers: Resistance, Potentiometric device, Resistance strain gauge, Resistance thermometer, Thermistor, Photoconductive cell, Inductance (LVDT), Capacitance, Voltage and current Devices using Hall effect, Photoemissive cell, Photomultiplier tube

Basic Requirements

  • Linearity: Input-output characteristics should be linear.
  • Ruggedness: Should withstand overloads with overload protection measures.
  • Repeatability: Identical output signals for the same input signal under the same conditions.
  • High stability and reliability: Output unaffected by environmental variations, minimum error in measurements.
  • Good dynamic response: Respond quickly to changes in input.
  • Convenient instrumentation: Produce a sufficiently high analog output signal with high signal-to-noise ratio.
  • Good mechanical characteristics: Should not deform under external forces.

Types of active and passive transducers

Active TransducerPassive Transducer
Photovoltaic, Thermoelectric, Piezoelectric, ElectromagneticVariable Resistance (Strain Gauge, Photo Conductors, Thermistor), Variable Reactance (Inductive, Capacitive)

Displacement Transducer

  • An electromechanical device used to convert mechanical motion or vibrations into variable electric signals.

Types

  • Capacitive Transducer
  • Inductive
    • Variable Inductance
    • Linear Variable Differential Transformer [LVDT]

CAPACITIVE TRANSDUCER

  • Capacitance of a parallel-plate capacitor: C = \frac{\varepsilon A}{d} where:
    • C = Capacitance
    • A = area of each plate in m²
    • d = distance between parallel plates in m
    • \varepsilon = \varepsilon0 * \varepsilonr = Permittivity
    • \varepsilon_r = relative dielectric constant
    • \varepsilon_0 = dielectric constant (permittivity) of free space in F/m
  • Capacitance is directly proportional to the area and inversely proportional to the distance between the plates.
  • Used to measure static and dynamic changes.
  • Drawback: Sensitivity to temperature variations.

INDUCTIVE TRANSDUCER

  • Measures force by the change of inductance in a single coil due to changes in the air gap when force is applied to a ferromagnetic armature.
  • Enables static and dynamic measurements.
  • Drawback: Limited frequency response.

LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT)

  • Consists of a primary coil and two secondary coils with a magnetic core. AC is fed into the primary, inducing voltages V{01} and V{02} in the secondary coils.
  • Output voltage V = V{01} - V{02}. At the null position, V{01} = V{02}, so V = 0.
  • Displacement of the core changes the induced voltages and produces a differential voltage output.
  • Output voltage is linear over a considerable range but flattens out at both ends, and the voltage phase changes by 180° as the core moves through the center position.
  • Provides continuous resolution and shows low hysteresis.
  • Sensitive to vibrations and temperature.
  • Requires receiving instrument to operate on AC signals or a demodulator network for DC output.
Advantages, Disadvantages, and Applications
  • Advt:
    1. High Range -1.25mm to 250mm.
    2. Low hysteresis
    3. Simple, light in weight and easy to maintain.
    4. Low Power Consumption
  • Disadvt:
    1. Sensitive to stray magnetic fields but shielding is possible.
    2. Temperature affects the performance of transducer.
  • Uses:
    1. Used in all applications where displacements ranging from a fraction of a mm to a few cm have to be measured.
    2. Acting as a secondary transducer it can be used as a device to measure force, weight, and pressure.

Thermoelectric Transducers

  • Converts Temperature to an electrical signal or electrical signal to temperature.

Types

  • Thermistor: Exhibits a large change in resistance proportional to a small change in temperature.
  • Thermocouple: Converts thermal potential difference into electric potential difference.

Thermistor

  • A type of resistor whose electrical resistance varies with changes in temperature.
  • Accurate, cheap, and robust way to measure temperature.
  • Does not work well in extremely hot or cold temperatures.
Construction
  • Made of oxides of metals such as Nickel, Manganese, Cobalt, Copper, Uranium etc.
  • Available in a variety of shapes and sizes.
    • Disk Type
    • Bead Type
    • Rod Type
Working Principle
  • Change in resistance due to a change in temperature.
  • The ambient temperature changes the thermistor starts self-heating its elements.
  • its resistance value is changed with respect to this change in temperature.
Types of thermistors
  • NTC:
    • NTC stands for Negative Temperature coefficient.
    • The resistance of an NTC will decrease with increasing temperature in a non-linear manner.
  • PTC:
    • PTC thermistors are Positive Temperature Coefficient resistors
    • The resistance of a PTC will increase with increasing temperature in a non-linear manner.
    • The PTC thermistor shows only a small change of resistance with temperature until the switching point(TR) is reached.
Advantages
  • Less expensive.
  • More sensitive than other sensors.
  • Fast response.
  • Small in size.

Disadvantages

  • Limited Temperature range.
  • Resistance to temperature ratio correlation is non-linear.
  • An inaccurate measurement may be obtained due to the self-heating effect.
  • Fragile.
Applications
  • NTC Thermistor
    • Digital Thermostats.
    • Thermometers.
    • Battery pack temperature monitors.
    • In-rush-current limiting devices
  • PTC Thermistor
    • Over-current protection
    • In-rush-current protection

Thermocouple

  • A temperature-measuring device consisting of two wires of different metals joined at each end.
  • One junction is placed where the temperature is to be measured, and the other is kept at a constant lower temperature.
  • The temperature difference causes the development of an electromotive force (known as the Seebeck effect) that is approximately proportional to the difference between the temperatures of the two junctions.
  • Thermocouple types are named according to the metals used to make the wires.
Applications
  • It is used to monitor the temperature in the steel and iron industries.
  • The principle of a thermocouple is used to measure the intensity of incident radiation.
  • It is used in the temperature sensors in thermostats to measure the temperature of the office, showrooms, and homes.
  • The thermocouple is used to detect the pilot flame in the appliances that are used to generate heat from gas like a water heater.
  • To test the current capacity, it is installed to monitor the temperature while testing the thermal stability of switchgear equipment.
  • The number of thermocouples is installed in the chemical production plant and petroleum refineries to measure and monitor temperature at different stages of the plant.

Piezoelectric Transducer

  • Uses the piezoelectric effect to measure changes in acceleration, pressure, strain, temperature or force by converting this energy into an electrical charge.

Working

  • Consists of a quartz crystal (SiO2) which is made from silicon and oxygen arranged in crystalline structure.
  • Piezoelectric crystals are electrically neutral and have balanced electrical charges.
  • Generates electrical polarity when mechanical stress is applied along a certain plane.
  • Compressive stress induces positive charges on one side and negative charges on the opposite side.
  • Tensile stress induces charges in reverse compared to compressive stress.

Applications

  • Used in automobile, proximity, and level sensors.
  • Medical diagnostics, infertility treatments, and in ultrasonic imaging for medical applications.
  • Motion and object identifiers, home security alarms, and pest deterrents.
  • Electric toothbrushes, inkjet printers, and buzzers.
  • Seismographs, accelerometers, and vibration detectors.
  • Evaluate detonations in engines and in automobile seat belts.
  • Sound pressure transformed into an electric signal in microphones.
  • Electric lighters in kitchens.

Hall Effect Transducer

  • Measures magnetic field by converting it into an EMF.

Principle

  • If a current-carrying strip of the conductor is placed in a transverse magnetic field, then the EMF develops on the edge of the conductor.

Applications

  • Magnetic to Electric Transducer
    • Used for converting the magnetic flux into an electric transducer.
    • Requires small space and gives the continuous signal concerning the magnetic field strength.
  • Measurement of Displacement
    • Measures the displacement of the structural element.
    • For example – Consider the ferromagnetic structure which has a permanent magnet.
  • Measurement of Current
    • Used for measuring the current without any physical connection between the conductor circuit and meter.
  • Measurement of Power
    • Measures the power of the conductor.

Photoelectric Transducer

  • Changes the energy from light to electrical energy.

Classification

  • Photo emissive Cell
  • Photodiode
  • Phototransistor
  • Photo-voltaic cell
  • Photoconductive Cell

Working Principle

  • In photoemissive type devices, once the radiation drops over a cathode can cause emission of electrons from the cathode plane.
  • The output of the PV cells can generate a voltage which is relative to the intensity of radiation.
  • In photo-conductive devices, the material’s resistance can be changed once it is light up.

Applications

  • Biomedical applications.
  • Pickups of pulse.
  • Pneumograph respiration.
  • Measure blood pulsatile volume changes.
  • Records Body movements.

Introduction to Opto-electronics Devices

  • Converts light energy to electrical energy and vice versa.

Types

  • Laser diode, light-emitting diode - convert electrical power into forms of light.
  • Photodiode, photo resistor, phototransistor, photomultiplier tube, solar cells -converts changing light levels into electrical form.

Major Developments

  • They have a longer wavelength.
  • They are easily fabricated materials.
  • They are of low cost.
  • They have high optoelectronic conversion efficiency.
  • These are Nano-scale devices.
  • They have high power light sources.

Light-dependent resistor (LDR) or Photo-resistor

  • An electronic component that is sensitive to light.
  • When light falls upon it, then the resistance value decreases.
Working Principle
  • As light falls on the semiconductor, the light photons are absorbed by the semiconductor lattice and some of their energy is transferred to the electrons.
  • The amount of energy transferred to the electrons gives some of them sufficient energy to break free from the crystal lattice so that they can then conduct electricity.
Characteristics
  • LDR’s are light-dependent devices whose resistance is decreased when light falls on them and that is increased in the dark.
  • When a light dependent resistor is kept in dark, its resistance is very high.
Types
  • Intrinsic light dependent resistor: Intrinsic photoresistors use un-doped semiconductor materials including silicon or germanium.
  • Extrinsic light dependent resistor: Extrinsic photoresistors are manufactured from semiconductor of materials doped with impurities.
Applications
  • Detect absences or presences of light like in a camera light meter.
  • Used in street lighting design.
  • Alarm clocks.
  • Burglar alarm circuits.
  • Light intensity meters.
  • Used as part of a SCADA system to perform functions such as counting the number of packages on a moving conveyor belt

Photodiodes

  • A class of diodes that converts light energy to electricity.
  • They are also called a photo-detector, a light detector, and a photo-sensor.
Working
  • A photodiode is subjected to photons in the form of light which affects the generation of electron-hole pairs.
  • If the energy of the falling photons is greater than the energy gap of the semiconductor material, electron-hole pairs are created near the depletion region of the diode.
Applications
  • Provide electric isolation.
  • Used in safety electronics such as fire and smoke detectors.
  • Used in numerous medical applications.
  • Used in solar cell panels.
  • Used in logic circuits.
  • Lighting regulation and optical communication.

Phototransistors

  • An electronic switching and current amplification component which relies on exposure to light to operate.
  • Capable of converting light energy into electrical energy.
Construction
  • Consists of an ordinary bi-polar transistor in which the base region is exposed to illumination
Working
  • Once the light strikes the base terminal & the light triggers the phototransistor by allowing the configuration of hole-electron pairs as well as the current flow across the emitter or collector.
Applications
  • Punch-card readers.
  • Security systems
  • IR detectors photo-electric controls
  • Computer logic circuitry.
  • Relays
  • Lighting control

Photovoltaic cells (solar cells)

  • Converts solar energy into useful electricity through a process called the photovoltaic effect
Photovoltaic Effect
  • Generates voltage or electric current in a photovoltaic cell when it is exposed to sunlight.
Layers of a PV Cell
  • Semi conductor Layer
  • Conducting material
  • Anti-reflection coating
Solar Cell Efficiency
  • There are ways to improve the efficiency of PV cells, all of which come with an increased cost.
  • Some of these methods include increasing the purity of the semiconductor, using a more efficient semiconducting material such as Gallium Arsenide, by adding additional layers or p-n junctions to the cell, or by concentrating the Sun's energy using concentrated photovoltaics.
Types of PV Cells
  • Silicon (Si)
  • Gallium Arsenide (GaAs)
  • Cadmium Telluride (CdTe)
  • Copper Indium Gallium Selenide (CIGS)

Optocoupler

  • Also called an opto-isolator, photocoupler, or optical isolator.
  • Transfers electrical signalis between two isolated circuits by using light.
Working
  • Components - LED & Photosensor
  • When the light hits the photosensor a current is conducted, and it is switched on.
  • When the current flowing through the LED is interrupted, the IR beam is cut-off, causing the photosensor to stop conducting.
Advantages
  • Optocouplers allow easy interfacing with logic circuits.
  • Electrical isolation provides circuit protection.
  • It allows wideband signal transmission.
  • It is small in size and lightweight device.
Disadvantages
  • The operational speed of Optocouplers is low.
  • In case of a very high power signal, the possibility of signal coupling may arise.
Applications
  • It is used in high power inverters.
  • It is used in high power choppers.
  • In AC to DC converters optocouplers are widely used.

Liquid crystal display (LCD)

  • A flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers.
  • Liquid crystals do not emit light directly, using a backlight or reflector to produce images in color or monochrome.
  • LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement.
Construction
  1. We must use polarized light.
  2. The liquid crystal should able be to control both of the operations to transmit or can also able to change the polarized light.
Working
  • When an electrical current is applied to the liquid crystal molecule, the molecule tends to untwist.
  • This causes the angle of light which is passing through the molecule of the polarized glass and also causes a change in the angle of the top polarizing filter.
Advantages
  • LCD’s consumes less amount of power compared to CRT and LED
  • LCD’s are consist of some microwatts for display in comparison to some mill watts for LED’s
  • LCDs are of low cost
  • Provides excellent contrast
  • LCD’s are thinner and lighter when compared to cathode-ray tube and LED
Disadvantages
  • Require additional light sources
  • Range of temperature is limited for operation
  • Low reliability and speed
Applications
  • LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage.
  • Small LCD screens are common in LCD projectors and portable consumer devices such as digital cameras, watches, digital clocks, calculators, and mobile telephones, including smartphones.
  • LCD screens are also used on consumer electronics products such as DVD players, video game devices and clocks.

Proximity sensor

  • A sensor able to detect the presence of nearby objects without any physical contact.

Operating Principles

  • Magnetic lost due to eddy currents
  • Changes in the capacitance between the sensing object and the Sensor
  • The reed end of the switch is operated by a magnet.

Applications

  • Parking sensors
  • Inductive sensors
  • Ground proximity warning system for aviation safety
  • Vibration measurements of rotating shafts in machinery
  • Mobile devices
  • Touch screens that come in close proximity to the face
  • Attenuating radio power in close proximity to the body, in order to reduce radiation exposure
  • Automatic faucets

IR Sensor

  • Emits the light in order to sense some object of the surroundings.
  • Measures and detects infrared radiation in its surrounding environment.

Types

  • Active infrared
  • Passive infrared

Applications

  • Proximity Sensor
  • Item Counter
  • Burglar Alarm
  • Radiation Thermometers
  • Human Body Detection
  • Gas Analyzers

Pressure Sensor

  • A transducer that senses pressure and converts it into an electric signal.
  • Pressure is defined as force applied to a unit of area (P=F/A)
  • A metal foil strain gage is a transducer whose electrical resistance varies with applied force,it converts force, pressure, tension, compression, torque, and weight into a change in electrical resistance, which can then be measured.

Types of pressure sensors

  • Absolute pressure sensor
  • Gauge pressure sensor
  • Vacuum pressure sensor
  • Differential pressure sensor
  • Sealed pressure sensor

Applications of pressure sensors

  • Automotive applications
  • Life-saving medical applications
  • Automated building applications
  • Life-enhancing consumer applications
  • Industrial applications

Introduction to Biosensor

  • Analytical devices which include a combination of biological detecting elements like a sensor system and a transducer.

Main components of a Biosensor

  • Sensor, transducer, and associated electrons.
  • The sensor is a responsive biological part.
  • The transducer is the detector part that changes the resulting signal from the contact of the analyte.

Working Principle of Biosensor

  • Analyte connects to the biological object to shape a clear analyte which in turn gives the electronic reaction that can be calculated.

Types of Biosensors

  • Electrochemical Biosensor
  • Physical Biosensor
  • Optical Biosensor
  • Wearable Biosensors

Biosensors Applications

  • These devices are applicable in the medical, food industry, the marine sector as they offer good sensitivity & stability as compared with the usual techniques.

Sensors for smart building

  • Dedicated to providing smart facilities to their workers and people while providing their users with an efficient and comfortable humanized building environment within the budget.

Popular Sensors

  • Passive Infrared (PIR) Sensors
  • Temperature & Humidity Sensors
  • Indoor Air Quality (IAQ) Room Sensors
  • Water Leak sensors
  • Thermal imaging
  • Ambient lighting
  • Door/cabinet open/close detection

Benefits of smart building sensors

  • Can save building energy
  • Improve the sustainability of building use
  • Real-time monitoring reduces maintenance costs
  • Optimize space utilization
  • Enhance the safety, comfort and safety of tenants

8 Marks Questions

  1. Explain the various torques associated with electrical measuring instruments.
  2. With neat sketch, explain the construction and working of PMMC instruments.
  3. With neat sketch, explain the construction and working of dynamometer type moving coil instruments.
  4. With neat sketch, explain the construction and working of attraction type moving iron instruments.
  5. With neat sketch, explain the construction and working of repulsion type moving iron instruments.
  6. With neat block diagram, explain digital multimeter(DMM). List out its advantages and disadvantages.
  7. With neat block diagram, explain digital storage oscilloscope (DSO). List out its advantages and disadvantages and applications.
  8. List out the basic requirements of a transducer and explain.
  9. With neat sketch, explain the construction and working of a capacitive transducer.
  10. With neat sketch, explain the construction and working of a LVDT. Also list out its advantages, disadvantages and applications.
  11. Explain various sensors used for smart buildings. List out its benefits.

4 Marks Questions

  1. Compare active and passive transducer with examples.
  2. Write short notes on:
    • Thermistors
    • Thermocouple
    • Piezoelectric transducer
    • Photoelectric transducer
    • Hall effect transducers
    • Light Dependent Resistor (LDR)
    • Photodiodes
    • Phototransistors
    • Photovoltaic cells (solar cells)
    • Opto-couplers
    • Liquid crystal display(LCD)
    • Proximity sensor
    • IR sensor
    • Pressure sensor
    • Bio sensor