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Instrumentation for Test & Measurement

Based onthe

Sensor Technology Handbook

•A sample of the 572 slides

in the course

The Course• Based on the “Sensor Technology Handbook”

edited by Jon Wilson, published by Newnes/Elsevier, copyright 2005, 691 pages plus CD.

• Some slides contain figure numbers. They refer to the book figures.

• This course covers only the highlights of the book.

• For discount order form, contact instructor.

Performance Characteristics

• Transfer Function– Curve of Output/Input

• Sensitivity– Slope of Transfer Function

• Span or Dynamic Range– Usable Range of Inputs

• Accuracy or Uncertainty– Largest Expected Error

• Hysteresis– Output Difference, Increasing & Decreasing

Performance Characteristics (2)

• Nonlinearity (Linearity)– Deviation of Transfer Function From Straight Line

• Noise– Extraneous Output Added to Signal

• Resolution– Minimum Detectable Signal Fluctuation

• Related to Noise Spectrum

• Bandwidth & Frequency Response– Usable Frequency Range & Variation of Sensitivity

Some Sensor Characteristics

Smart Sensors

The Measurement

• Expected Amplitude Range

• Expected Frequency Range

• Expected Environment

• Economic Constraints

• Installation Constraints

• Available Instrumentation

The Data Sheet

• Filtering the Data Sheet

• What is Pertinent?

• Interpreting the Data Sheet

• Getting Clarification– Literature

– Experts & Consultants

– Manufacturers

System Considerations

• Sensor Characteristics

• Interconnections

• Signal Conditioner Characteristics

• Data Acquisition Characteristics

• Readout Characteristics

• Data Validation

• Analysis and Interpretation

Instrument Selection

• Sensor Environment• Sensor Performance Characteristics• Sensor Electrical Characteristics• Sensor Size and Weight• Sensor Mounting• Cable Environment• Cable Performance Characteristics• Cable Mechanical Characteristics

Instrument Selection (2)

• Power Supply Environment

• Power Supply Performance

• Power Supply Size and Weight

• Amplifier Environment

• Amplifier Performance

• Amplifier Size and Weight

Quantifiable Measurements

• REQUIRE:

• What is the Measurand?

• What is the Environment?

• What Uncertainty (Accuracy) is Required?

• Whole System Calibrated & Traceable?

• Appropriate Sensor is Necessary, But Not Sufficient.

Sensor Resistances

Bridge Configurations

Minimizing Offset Errors

Noise Sources

DC Errors

ADC TypesADC’S FOR SIGNAL CONDITIONING

Successive Approximation• Resolutions to 16-bits• Minimal Throughput Delay Time• Used in Multiplexed Data Acquisition SystemsSigma-Delta• Resolutions to 24-bits• Excellent Differential Linearity• Internal Digital Filter, Excellent AC Line Rejection• Long Throughput Delay Time• Difficult to Multiplex Inputs Due to Digital Filter Settling TimeHigh Speed Architectures:• Flash Converter• Subranging or Pipelined

PE Amplifier Circuit

CCD Arrays

Technology Fundamentals

• Piezoelectric

• “Crystal” type

• Self-generating

• Piezoelectric materials– Natural (monocrystalline)

– Piezoceramic (polycrystalline)

IEPE Sensor System

MEMS PR Construction

MEMS VC Accelerometer

Selection Process

• Frequency range?

• Sensitivity or amplitude range?

• Environment, especially temperature?

• Size and mass restraints?

• Mounting configuration?

• Consult manufacturer’s application engineers?

Interfacing and Designs

Overview

Biosensor characteristics

• Sensitivity• Selectivity• Range• Response time• Reproducibility• Detection limit• Life time• Stability

Transduction Mechanisms

• Amperometry• Potentiometry• Photometry• PE materials• Conductimetric• Thermometric• Enzyme thermistor• FET transducer

Biosensor configurations

Mass Spectrometer Schematic

Mass Spectrometer

Inductive Sensors

• “Eddy current sensors”

• Require conductive targets

• Not affected by gap material

• Sensitive to target material

• Nanometer resolutions

• > 80 kHz

• Minimum target thickness requirement

Selecting and Specifying

• Physical configuration

• Output, Range

• Offset, Standoff

• Sensitivity, Linearity, Resolution

• Bandwidth

• Thermal errors

• Accuracy

Comparing Capacitive and Inductive Sensors

Latest Developments

• Little change in sensors

• Advances in electronics

• Miniaturization

• Embedded electronics

• Digital interface

Inductive Sensor (LVDT)

Hall Effect Sensor

10. Flow and Level Sensors

Mass, volume, laminar, turbulent flow. Hydrostatic, ultrasonic, RF capacitance,

magnetostrictive, microwave level.

Methods for Measuring Flow

• Thermal anemometers• Differential pressure• Vortex shedding• Positive displacement• Turbine-based• Mass (Coriolis)• Electromagnetic• Ultrasonic• Laser

11. Force, Load & Weight Sensors

Piezoelectric & Strain Gage

Load Cell

12. Humidity Sensors

Capacitive, resistive & thermal conductivity

Selecting and Specifying

• Accuracy, Repeatability, Interchangeability

• Stability, Condensation recovery

• Contamination resistance, Size & packaging

• Cost effectiveness, replacement cost

• Calibration

• Complexity of signal conditioning

Interfacing and Design

• Output affected by temperature & RH

• Temperature compensation required for best accuracy

• Industrial grade sensors incorporate RTD on the ceramic substrate

• RHIC output depends on supply voltage, RH and temperature

Photosensors

• Quantum detectors convert photons to electrons

• Thermal detectors absorb radiant energy and measure temperature change

IR Detector Spectral Responses

16. Pressure Sensors

Gauge

Absolute

Differential

Many technologies

• Silicon strain gages (Piezoresistive)

• Variable reluctance

• Variable capacitance

• Fiber optic

• Piezoelectric

• (Every company that makes any kind of sensor makes pressure sensors)

Types of pressure measurement

• Gauge

• Differential

• Absolute

• Vacuum gauge

• All are actually differential, with different references

Latest & Future

• Miniaturization

• Higher temperatures

• Sensor identification– Smart sensors (IEEE1541)

– SAW tag

• Wireless

20. Temperature Sensors

Basic types

• Contact: the sensor is in contact with the medium or object being measured

• Non-contact: interprets the radiant energy of a heat source in the form of infrared radiation– Useful on non-reflective solids and liquids

– Not useful with gases because of their transparency

21. Nanotechnology-Enabled Sensors

Smaller than small; atomic level

More possibilities

• Increasing integration of materials, devices and systems

• “nanotech takes the complexity out of the system and puts it into the material”

• Single molecule detection

• Nanotech data storage 10^12 bits/sq. in.

• High volume production of tiny, low-power smart sensors

Nano-array of Cantilevers & Electronics

Introduction to Wireless Sensor Networks

• Increase reliability of data gathering

• Reduce deployment costs

• Minimize long term maintenance costs

• Reduce cabling and connector costs

• Ideal system is networked and scalable– Low power, smart, programmable, fast data rate,

reliable, accurate, stable

• Integrated sensor, electronics, communication

Industrial Application