Sensors for Industrial Inspection, 1993

Numerous areas of expertise are often required for the inspection of an individual product, with many different sensors being used within a single inspection machine. For this reason it is necessary for the production engineer to have at least a working knowledge of all the different technologies that may be employed.
This book covers the majority of sensors that can be applied on the shop floor and has been designed to assist engineers with little or no previous experience in the various fields. The information that the book contains is of a highly practical nature and is based on the author's considerable first-hand experience of varied industrial applications.

1. Fundamentals of Sensor Materials.- 1.1 Introduction.- 1.2 Atomic Structure.- Ionisation Potential.- 1.3 Crystalline Structure.- 1.4 Electron Energies.- 1.5 Semiconductors.- 1.6 Resistance.- Strain Gauges.- Thermistors.- Thermocouples.- 1.7 Thermal Radiation.- 1.8 Photoelectric Effects.- 1.9 Photon Emission.- Luminescence.- Photodiodes.- 1.10 Piezoelectric Effects.- Ferroelectric Effect.- 2. Distance.- 2.1 Introduction.- 2.2 Ultrasonic Ranging.- Ultrasonic Transducers.- Resolution.- Interference.- Pulse Rate.- Beam Angle.- Range.- Velocity of Sound.- Doppler Effect with Moving Targets.- Environmental Considerations.- Installation Techniques.- Sensor Interfacing.- 2.3 Optical Techniques.- Time of Flight.- Pulse/Echo.- Phase Differences.- Triangulation Techniques.- Ranging using Focus.- Optical Displacement Sensor.- Range from Brightness.- Zone Distance Sensors.- Visual Scaling.- Optical Interferometry and Diffraction Systems.- Photographic Camera Ranging Techniques.- 2.4 Capacitive Distance Sensors.- 2.5 Inductive Distance Sensors.- 2.6 Air Gauge.- 2.7 X-ray Thickness Gauging.- 2.8 LVDT.- 2.9 Magneto-Acoustic Sensor.- 2.10 Time Domain Reflectometer.- 2.11 Rotary / Linear Encoders.- Optical Encoders.- Rotary/Linear potentiometers.- 2.12 Thickness Measurement.- Ultrasonic Thickness Gauging.- 3. Movement.- 3.1 Introduction.- 3.2 Velocity.- Doppler Effect.- 3.3 Accelerometers.- Piezoelectric Accelerometers.- Piezoresistive Accelerometers.- Variable Capacitance Accelerometers.- Force Balancing Accelerometers.- Environmental Considerations.- Mounting Considerations.- Electrical Interfacing.- 3.4 Flow Measurement.- Pressure Difference Flow Meters.- Frequency Shift Flow Meter.- Transit Time Flowmeter.- Hot Wire Anemometer.- Rotating Vanes.- Electromagnetic Flow Sensing.- 3.5 Tachometers.- AC / DC Generators.- Optical Tachometers.- 3.6 Vibration.- Machine Vibration Measurement.- 3.7 Tilt Switches.- 4. Proximity Sensors.- 4.1 Introduction.- Application Example.- 4.2 Inductive Proximity Switches.- Inductive Sensing.- Skin Effect.- Magnetic Inductive Proximity Sensors.- Mounting Considerations.- Hysteresis.- Target Approach.- Body Styles and Sizes.- Welding Proof.- Applications.- 4.3 Capacitive Proximity Sensors.- Capacitive Sensing.- Target Materials.- 4.4 Photoelectric Proximity Switches.- Photoelectric Sensing.- Sensor Configurations.- 4.5 Interfacing Proximity Sensors.- 5. Tactile Sensors.- 5.1 Introduction.- 5.2 Resistive techniques.- Conductive rubber.- Conductive Plastics.- Carbon Fibre.- Tactile Arrays.- 5.3 Piezoelectric Effect.- Piezoelectric Film.- 5.4 Magnetic effects.- Magnetoresistance.- Magnetoelastic & Magnetostrictive Materials.- 5.5 Optical Techniques.- Touch Vision.- Touch Finger.- 5.6 3-D Tactile Sensors.- 6. Surface Finish.- 6.1 Introduction.- 6.2 Stylus Instruments.- Stylus Protection.- Stylus Selection.- Mounting Arrangements.- Laser Stylus.- 6.3 Profile Analysis.- Sample and Assessment Lengths.- 6.4 Surface Reflection.- Roughness and Waviness from Surface Scattering.- 6.5 Laser Scanning.- Polarised Laser Scanning.- 6.6 Visual Analysis of Texture.- Statistical Classification.- Structural Approaches.- Spectral Approaches (Fourier Analysis).- 6.7 Optical Sectioning (Structured Light).- 6.8 Roughness Gauging.- 6.9 Crack Detection.- 7. Structural Analysis.- 7.1 Introduction.- 7.2 Photoelastic Stress Analysis.- Stress Direction.- Stress Magnitude.- Stress Polarity.- 3-D Model Analysis.- Stress Freezing.- 7.3 Thermoelastic Stress Analysis.- 7.4 Transient Thermography.- 7.5 Acoustic Emission — Stress Wave Sensing.- Individual Transients.- Multiple Transients.- Continuous Emission.- Applications.- Locating the Source.- Sensor Design.- 7.6 X-ray Inspection.- 7.7 Gamma-Radiation.- 7.8 Beta-Particles.- 7.9 Viscosity.- 7.10 Eddy current sensing.- 7.11 Ultrasonic Inspection.- Compression and Shear Waves.- Velocity.- Wavelength.- Probe Design.- Data Acquisition and Display.- 7.12 Acoustic Flaw Detection.- 7.13 Hardness Testing.- 8. Temperature Sensing.- 8.1 Introduction.- Units of Temperature.- 8.2 Metallic Resistance Thermometers.- Platinum Resistance Thermometers.- Linearity.- Installation.- Low Temperature Resistance Sensors.- 8.3 Thermistors.- Thermal Characteristics.- Current Limiting Applications.- Positive Temperature Coefficient Thermistors (PTC).- Installation Considerations.- 8.4 Thermocouples.- Seebeck Effect.- Thermocouple Types.- Thermocouple Materials.- Thermocouple Construction.- Law of Intermediate Metals.- Cold junction compensation.- Connecting Cables.- Temperature Transmitters.- 8.5 Semiconductor Temperature Measurement.- Silicon Junction Diode.- Semiconductor Temperature Sensors.- Temperature Sensing Integrated Circuits.- 8.6 Optical Pyrometers.- Infrared theory.- Planck’s Law.- Black bodies.- Radiation Detectors.- Application Considerations.- 8.7 Thermal Imaging.- 8.8 Disappearing Filament.- 8.9 Thermographic Materials.- Temperature sensitive pigments.- Liquid crystals.- 8.10 Thermographic Phosphors.- 8.11 Distributed Fibre Optic Temperature Sensors.- Raman Scattering.- Applications.- 8.12 Thermostats.- Bimetallic Elements.- 8.13 Ceramic Temperature Sensors.- Cooling System Control Application.- 9. Pressure Sensing.- 9.1 Introduction.- 9.2 Capacitance Manometers.- 9.3 Quartz Pressure Sensors.- Electrostatic Pressure Sensors.- Quartz Resonant Pressure Sensors.- 9.4 Piezoresistive Pressure Sensors.- 9.5 Strain Gauge Pressure Sensors.- 9.6 LVDT Pressure Transducer.- 9.7 Silicon Pressure Sensors.- 9.8 Vacuum Gauges.- Thermal Conductivity Gauges.- Thermocouple Gauge.- Pirani Gauge.- Thermistor Gauge.- Ionisation Gauges.- 10. Weight.- 10.1 Introduction.- 10.2 Check Weighers.- 10.3 Dynamic Weighing Systems.- 10.4 Hydraulic and Pneumatic Weighing Systems.- 11. Moisture/Humidity.- 11.1 Introduction.- 11.2 Dew Point Instruments.- 11.3 Vapour Pressure Methods / Relative Humidity.- Absolute Humidity of a Gas Mixture.- Relative Humidity of a Gas Mixture.- Equilibrium Relative Humidity.- 11.4 Infrared Moisture Measurement.- Infrared Moisture Sensor.- Infrared Absorption.- 11.5 Microwave Techniques.- 11.6 Quartz Crystal Oscillator.- 11.7 Conductivity.- 11.8 Capacitance Sensors.- 11.9 Diffusion Cell Electrolyte.- 11.10 Calibration.- 12. Gas Detection.- 12.1 Introduction.- Combustible Gas Detectors.- Toxic Gas Detectors.- Sensor Location.- 12.2 Electrochemical Sensors.- 12.3 Semiconductor Detectors.- 12.4 Catalytic Detector (pellistor).- 12.5 Conducting Polymer Gas Detectors.- 12.6 Infrared Spectroscopy.- Molecular Vibrations.- Absorption of Infrared Light.- Photoacoustic Spectroscopy.- 12.7 Thermal Conductivity Detector (TCD).- Katharometer.- 12.8 Photo-Ionisation detector (PID).- 12.9 Ultrasonic Detectors.- 12.10 Paramagnetic Oxygen Analysers.- Magnetic Wind Instruments.- 12.11 Flame Ionisation Detectors (FID).- 12.12 Units of Gas Concentration.- 13. Light and Colour Measurement.- 13.1 Introduction.- 13.2 Units of Light Measurement.- Luminous Flux.- Luminous Intensity.- Illuminance.- 13.3 The Nature of Colour.- Hue.- Saturation.- Intensity.- 13.4 Human Perception of Colour.- Colour Discrimination.- 13.5 CIE Standards.- The Standard Observer.- Colour Sensitivity of the Human Eye.- CIE Chromaticity Diagram.- XYZ System.- Yxy Colour System.- The Lab system.- 13.6 Munsell Colour Wheel.- 13.7 RGB Systems.- RGB Colour Space.- Colour Triangle.- 13.8 Colour Mixing.- Additive and Subtractive Colour Mixing.- Complimentary Colours.- 13.9 Illumination.- Colour Temperature.- Light Sources.- Man Made Light Sources.- Natural Light Sources.- Filters.- Atmospheric Absorbtion.- 13.10 Colour Pigments.- 13.11 Colour Matching.- Metamerism.- 13.12 Colour Measuring Equipment.- Colour Sensing.- Densitometers.- Effects of Polarisation.- Chromameters.- Illuminance Meters.- Luminance Meters.- Spectrophotometers.- Spectral Filter Arrays.- 14. Optics.- 14.1 Introduction.- 14.2 Light — Fundamentals.- 14.3 Laws of optics.- Reflection.- Absorption and Transmission.- Refraction.- Diffraction.- 14.4 Lenses.- Real and Imaginary Images.- Bi-convex Lenses.- Bi-concave Lenses.- Ray Diagrams.- Prisms.- Fresnel Lenses.- Depth of Field — Depth of Focus.- Aperture.- Measuring the Focal Length of an Unknown Lens.- 14.5 Mirrors.- Prism Reflectors.- 14.6 Lens Systems.- Magnifying glass.- Photocopier.- Projector.- 14.7 Lens Defects.- Spherical Abberation.- Chromatic Aberration.- 14.8 Polarised Light.- Polarisation by Reflection.- Double Refraction.- Optical Rotation.- 14.9 Interference Filters.- Band Pass Filters.- Filter Factors.- Correction Filters.- Contrast Filters.- Dichroic Filters.- 14.10 Holography.- 15. Lighting.- 15.1 Introduction.- 15.2 Methods of Illumination.- Front lighting.- Specular Illumination (dark field).- Specular Illumination (light field).- Beam Splitter.- Split Mirror.- Shadow Illumination.- Backlit Illumination.- Retroreflector.- Back Illumination (condenser).- Rear Illumination (collimator).- Rear Offset Illumination.- Structured Light.- Ring Lights.- Diffuse Scattering.- Fibre Optic Light Sources.- Surface Characteristics.- Distribution and Spread of Illumination.- 15.3 Colour.- Spectral Characteristics.- Daylight.- 15.4 Lighting Power Supplies.- Frequency — Ripple and Drift.- Colour Temperature.- Run Up.- High Frequency Operation.- 15.5 Handling Heat Dissipation.- Dichroic Reflectors.- 15.6 Protection Against Lamp Shattering.- 15.7 Lamp Life.- Pre-Ageing of Lamps.- Efficiency.- 15.8 Incandescent lamps.- 15.9 Tungsten Halogen Lamps.- Installation Considerations.- 15.10 Fluorescent Lamps.- Luminescence.- Fluorescent Lamp Output.- High Frequency Fluorescents.- 15.11 Sodium Vapour Discharge Lamps.- 15.12 Neon Lamps.- 15.13 Electronic Flash Tubes.- Xenon Flash Lamps.- 15.14 UV Illumination (black light lamps).- 15.15 Light Emitting Diodes (LED’s).- 15.16 Electroluminescence.- Electroluminescent Panels.- 15.17 Lasers.- Gas lasers.- Semiconductor Lasers.- Laser Safety.- 16. Cameras.- 16.1 Introduction.- Solid State Camera Arrays.- Advantage of Solid State Devices.- 16.2 Vidicon Cameras.- Exposure and Scanning.- Dark Current.- Colour Vidicons.- Choice of Target for Vidicons.- 16.3 Photodiode Arrays.- 16.4 Charge Coupled Devices (CCD’S).- Transfer of Charge.- Infrared Sensitivity.- Photosite Shapes.- Area Arrays.- Colour CCD Arrays.- 2 D Images on Linear Arrays.- Very High Resolution 2 D Cameras.- Hexagonal Arrays.- Circular Arrays.- 16.5 Charge Injection Devices (CID’s).- 16.6 Ram Cameras.- 16.7 Camera Specification & Performance.- Resolution.- Sensitivity.- Crosstalk.- Linearity and Gamma.- Geometrical Faults.- Blooming.- Lag.- Noise.- Dark Signal.- 16.8 Image Intensifies.- Channel Plate Intensifier.- 16.9 Scanning Rates.- Short Exposures.- Video Images.- 16.10 Flying Spot Laser Scanners.- Direction of Reflection.- Dimension Measurement.- 17. Image Processing.- 17.1 Introduction.- Nomenclature and Standards.- 17.2 Thresholding.- Fixed Level Thresholding.- Dynamic Thresholding.- Adaptive Thresholding.- Multi-Level Thresholding.- Spatially Varying Thresholds.- Colour Thresholding.- Threshold Implementation.- 17.3 Grey Scale Transformations.- Histogram Equalisation.- Contrast Expansion.- Square intensity.- 17.4 Multiple Image Averaging.- 17.5 Filtering / Convolutions.- Mean (Average).- Median Filter.- High Pass.- Low Pass.- Lightest.- Darkest.- Intermediate Results.- 17.6 Edge Detection.- Horizontal gradient.- Vertical Gradient.- Sobel.- Dispersion.- Goodman-Smyth.- Roberts.- Laplace.- Complex Edge Detectors.- 17.7 Image Transformation.- Spatial Transformations.- 18. Application of Machine Vision.- 18.1 Introduction.- 18.2 A Low Cost Commercial Vision System.- System Specification.- Inspection Procedure.- Simple Thresholds.- XY Float.- Window Measurements.- Line Gauge Measurements.- 18.3 Area Array Camera Applications.- Inspection of a Plastic Moulded Plug Top.- Clothes Peg.- Edge Enhancements.- 18.4 Line Scan Camera Applications.- Line Scan Cameras for 2-D Image Capture.- Line Scan Camera Measurement Systems.- Lighting Considerations.- Alignment and Focusing.- ‘Ruler’ Applications.- Biscuit Width & Colour Measurement.- 18.5 Colour Inspection.- Benefits of using Colour.- Colour System Selection.- Chocolate Biscuit Inspection.- Colour Sorting.- Orange Picking.- Commercial Organisations.- References.