Smart Sensor Systems Nurbek P Saparkhojayev Ph D

Smart Sensor Systems Nurbek P. Saparkhojayev, Ph. D

Definition of a sensor • Def. 1. (Oxford dictionary) • A device giving a signal for the detection or measurement of a physical property to which it responds. • Def. 2. • A sensor is a device that receives a signal or stimulus and response with an electrical signal.

Definitions • Transducer: a device that converts one form of energy into another. (преобразователь) • Sensor: a device that converts a physical parameter to an electrical output. (датчик) • Actuator: a device that converts an electrical signal to a physical output. (силовой привод)

More. . American National Standards Institute (ANSI) Definition • A device which provides a usable output in response to a specified measurand • A sensor acquires a physical parameter and converts it into a signal suitable for processing (e. g. optical, electrical, mechanical) • A transducer • Microphone, Loud Speaker, Biological Senses (e. g. touch, sight, …ect)

Detectable phenomenon of sensors Stimulus Acoustic Biological & Chemical Electric Magnetic Quantity Wave (amplitude, phase, polarization), Spectrum, Wave Velocity Fluid Concentrations (Gas or Liquid) Charge, Voltage, Current, Electric Field (amplitude, phase, polarization), Conductivity, Permittivity Magnetic Field (amplitude, phase, polarization), Flux, Permeability Optical Refractive Index, Reflectivity, Absorption Thermal Temperature, Flux, Specific Heat, Thermal Conductivity Mechanical Position, Velocity, Acceleration, Force, Strain, Stress, Pressure, Torque

Classification of sensors Attributes which can be used to classify sensors: . stimulus. working principle. properties (attributes of the characteristic). application

Classification of sensors

1. Active and passive sensors Active sensor: a sensor that requires external power to operate. Examples: the carbon microphone, thermistors, strain gauges, capacitive and inductive sensors, etc. Other name: parametric sensors (output is a function of a parameter - like resistance) Passive sensor: generates its own electric signal and does not require a power source. Examples: thermocouples, magnetic microphones, piezoelectric sensors. Other name: self-generating sensors Note: some define these exactly the other way around

2. Contact and noncontact sensors Contact sensor: a sensor that requires physical contact with the stimulus. Examples: strain gauges, most temperature sensors Non-contact sensor: requires no physical contact. Examples: most optical and magnetic sensors, infrared thermometers, etc.

3. Absolute and relative sensors Absolute sensor: a sensor that reacts to a stimulus on an absolute scale: Thermistors, strain gauges, etc. , (thermistor will always read the absolute temperature) Relative scale: The stimulus is sensed relative to a fixed or variable reference. Thermocouple measures the temperature difference, pressure is often measured relative to atmospheric pressure.

4. Other schemes Classification by broad area of detection • • • Electric sensors Magnetic Electromagnetic Acoustic Chemical Optical Heat, Temperature Mechanical Radiation Biological Etc.

4. Other schemes (cont. ) Classification by physical law • • • • Photoelectric Magnetoelectric Thermoelectric Photoconductive Magnitostrictive Electrostrictive Photomagnetic Thermoelastic Thermomagnetic Thermooptic Electrochermical Magnetoresistive Photoelastic Etc.

4. Other schemes (cont. ) Classification by specifications • • • • Accuracy Sensitivity Stability Response time Hysteresis Frequency response Input (stimulus) range Resolution Linearity Hardness (to environmental conditions, etc. ) Cost Size, weight, Construction materials Operating temperature Etc.

4. Other schemes (cont. ) Classification by area of application • • • • Consumer products Military applications Infrastructure Energy Heat Manufacturing Transportation Automotive Avionic Marine Space Scientific Etc.

Classification of actuators All of the above In addition: Classification of actuators by type of motion • Linear • Rotary • One-axis • Two-axes • Three-axes • Etc.

Classification of actuators • Low power actuators • High power actuators • Micropower actuators • Etc.

Sensing and actuating strategies Look at sensors based on broad area of detection Discuss actuators wherever they fit with sensors Concentrate on the major classes Emphasize compatibility of classes of sensors and actuators.

Requirements for interfacing Needs: • Matching (impedances, voltages, currents, power) • Transformations (AC/DC, DC/AC, A/D, D/A, Vto. F, etc. ) • Matching of specifications (temperature ranges, environmental conditions, etc. ) • Alternative designs • Etc.

Connection of sensors/actuators • The processor should be viewed as a general block • • Microprocessor Amplifier Driver Etc. • Matching: between sensor/processor and processor/actuator

Example - Temperature control • Sense the temperature of a CPU • Control the speed of the fan to keep the temperature constant

Temperature control - implementation • Sometimes the A/D and signal conditioning are separate from the processor • The whole circuitry may be integrated into a “smart sensor” • Match: impedance at input to amplifier and at processor

Temperature control - Alternative design • Simpler (uses an integrated sensor that contains some of the necessary circuitry). May still require an A/D • The performance of this design is not the same (range is 0 -85 C while the previous design was 200 to 2000 C or more)

Units • SI units in most cases • Standard units when understanding warrants it (e. g. psi for pressure) • Will avoid mixed units (a common problem in sensors and actuators)

Measurements Heisenberg (1927): ”The momentum and position of a particle can not both be precisely determined at the same time. ” Measuring activity disturbs the physical process (loading effect). Measurement error: That is the difference between the measured value and the true value. error = measured value - true value Deterministic errors: They are repeated at every measurement, e. g. reading offset or bias. Such errors can be corrected by calibration. Random errors: They are caused by several parameters and change in time in an unpredictable fashion. They can be quantified by mean errors, standard deviation. Precision: Measurements with small deviation Accuracy: Measurements with small errors, i. e. small bias and high precision.

Sensor properties output factual ideal input A sensor should represent a physical variable as fast and as accurately as possible. A sensor is represented by its characteristic. Ideally, the sensor characteristic is a straight line

Physical Principles • Amperes’s Law • A current carrying conductor in a magnetic field experiences a force (e. g. galvanometer) • Curie-Weiss Law • There is a transition temperature at which ferromagnetic materials exhibit paramagnetic behavior • Faraday’s Law of Induction • A coil resist a change in magnetic field by generating an opposing voltage/current (e. g. transformer) • Photoconductive Effect • When light strikes certain semiconductor materials, the resistance of the material decreases (e. g. photoresistor)

Need for Sensors • Sensors are omnipresent. They embedded in our bodies, automobiles, airplanes, cellular telephones, radios, chemical plants, industrial plants and countless other applications. • Without the use of sensors, there would be no automation !! • Imagine having to manually fill Poland Spring bottles

Choosing a Sensor

Temperature Sensor • Temperature sensors appear in building, chemical process plants, engines, appliances, computers, and many other devices that require temperature monitoring • Many physical phenomena depend on temperature, so we can often measure temperature indirectly by measuring pressure, volume, electrical resistance, and strain

Temperature Sensor • Bimetallic Strip • Application • Thermostat (makes or breaks electrical connection with deflection)

Temperature Sensor • Resistance temperature device.

Accelerometer • Accelerometers are used to measure along one axis and is insensitive to orthogonal directions • Applications • Vibrations, blasts, impacts, shock waves • Air bags, washing machines, heart monitors, car alarms • Mathematical Description is beyond the scope of this presentation. See me during lunch if interested

Light Sensor • Light sensors are used in cameras, infrared detectors, and ambient lighting applications • Sensor is composed of photoconductor such as a photoresistor, photodiode, or phototransistor

Magnetic Field Sensor • Magnetic Field sensors are used for power steering, security, and current measurements on transmission lines • Hall voltage is proportional to magnetic field

Ultrasonic Sensor • Ultrasonic sensors are used for position measurements • Sound waves emitted are in the range of 2 -13 MHz • Sound Navigation And Ranging (SONAR) • Radio Dection And Ranging (RADAR) – ELECTROMAGNETIC WAVES !!

Photogate • Photogates are used in counting applications (e. g. finding period of period motion) • Infrared transmitter and receiver at opposite ends of the sensor • Time at which light is broken is recorded

CO 2 Gas Sensor • CO 2 sensor measures gaseous CO 2 levels in an environment • Measures CO 2 levels in the range of 0 -5000 ppm • Monitors how much infrared radiation is absorbed by CO 2 molecules

The end of the lecture • Questions? • Comments? • Any ideas? • Thank you very much!!