Electronic instrumentation
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Electronic Instrumentation. European PhD – 2009 Transducers and Signal Conditioning Horácio Fernandes. Useful Signal. When converting a signal to a quantity, it is only useful if its representation is kept unchanged within a knew error

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Electronic instrumentation


European PhD – 2009

Transducers and Signal Conditioning

Horácio Fernandes

Useful signal

Useful Signal

  • When converting a signal to a quantity, it is only useful if its representation is kept unchanged within a knew error

  • Signal conditioning and transmission is very important in applied physics

Signal paths

Signal paths

  • Preserve signal quality

  • DAS less demanding

  • Preserve and adjust dynamic bandwidth

  • Resize operational limits

    • Offset

    • Amplitude

    • Bandwith

  • Linearization

  • Galvanic isolation

  • Buffering

Sensors and transducers

Sensors and Transducers


Device capable of changing one form of energy into another

Active – External power supply

Passive – Internal source (self-generating)


Changing of a characteristic in an electric circuit (R; L, C);

Generate an output signal proportional to the stimulus



Sensors transducer principles

Sensors Transducer Principles


Strain gauges: Force measurements (W. Bridges)

Temperature: RTDs, termistors

Light: photoelectric cells and photodiodes

Position: potentiometers as dividers, grids

Sensors transducer principles1

Sensors Transducer Principles



Dielectric constant

Geometric configuration

Cell chargers


LVDT –Differential Transformer

Hall Effect

Motors as generator

Sensors selection

Sensors Selection

Scale: limiting extremes (Worst Case)

multiples sensors for scale spanning


Least detected variation (resolution)


Temporal response

Dynamic response

Accuracy and resolution

Stress (consistency)

Reproducibility and hysteresis


Sensors operation

Sensors Operation




Extreme Temperatures

Water presence and moist

Chemical corrosion: solvers, acids e bases

Environmental protection

Susceptibility: eletric/explosion/chash

Sensors operation1

Sensors Operation

Human use


Corrosion/Chemicals manipulation




Electric Interference (EMI- high impedance, low current)

Sensors operation2

Sensors Operation


Circuit Charger (photocell)

Excitation source (noise)

Signal Conditioning

Physics size



Measurement Error – Comparison standard should be more exact than sensor resolution

Calibration table – Calibration curve

Physic model

Static and dynamic calibration


Impulsive response



  • Transfer function errors

    • Non-linearity

      • Sensor

      • Electronics

      • Signal path

  • Compensation

    • Non-linear electronic circuit

    • Piecewise interpolation



  • Source/Input isolation

    • Impedance adaptation

      • Maximum feed power

      • Voltage signal

  • Transducer output

    • Preserve signal

      • Next stage charge circuit

Meters and bridges

Meters and bridges

  • Differential mode

  • Common mode

Wheatstone bridge

Wheatstone Bridge

  • Potentiometer divider

  • Zero Measurement

  • CMR>100 dB

  • Sensibility

  • Thermal immunity

Wheatstone bridge application

Wheatstone BridgeApplication

Kelvin bridge

Kelvin bridge

  • Very low resistors (<1R)

  • Double terminals

Maxwell bridge

Maxwell Bridge

Bridges configurations

Bridges Configurations

Bridges circuits

Bridges circuits

  • AC generators

  • Current sources

  • OPAMPs applications

Bridge noise immunity

Bridge noise immunity

  • Pick-up noise

  • Cable resistance

  • Signal Bandwidth

  • 3-wire connection

Noise reduction

Noise reduction

  • …If noise blocking fails in the origin…

    …Nightmare begins!

What can we filter

What can we filter?

  • Signal sampling: analog goes digital at what rate?

  • Nyquist criteria: fs>2fmax

  • Low-pass filters (cutoff -40 dB)

  • Guard-band

  • Sampling band: [fs-fmax, fs+fmax]

Useful storage bandwith

Useful Storage Bandwith

  • Pratical figures

    • USB=fs/2.5

      • Sin Interpolation

    • USB=fs/10

      • Linear Interpolation

    • USB=fs/25

      • No Interpolation

    • USB=fs/4.6

      • Digital correction (factor 1.6) x (1/0.35)



Perceptual aliasing

Perceptual aliasing

Image aliasing

Image aliasing



  • Pass-band

  • Cut-off

  • Stop-band

  • Ripple

  • Order

  • Phase and amplitude characteristics

Common filters

Common Filters

  • Lowpass

  • Highpass

  • Passband

  • Notch

  • Digital filtering (made possible with fast ADCs)

    • Advantages: High order, cutoff frequency, complex transforms

    • Signal correlation

Other techniques

Other Techniques

  • Periodic signals

    • Lock-in amplifiers

      • Cross correlation

    • Boxcar integration

    • Multichannel mean

      • Overlap of periodic signals

      • S/N~N1/2

Other techniques1

Other Techniques

  • Pulsed signals

    • Constant Fraction


Transimpedance amplifier

Transimpedance amplifier

  • Allow very low current sources detection, ex: photodiodes

    • Tomography

    • Spectrometers

    • Line radiation filters

  • Charge measurements, ex: ion beam

  • High bandwidth

I v probes

I(V) probes

  • Current detection

    • Ground loop

    • Safety - galvanic isolation

    • Sweep waveforms – capacitive coupling and distortion

    • Fast sweeping – plasma limit operation

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