Chapter 5: Signal Conditioner

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Chapter 5 Signal Conditioner

• Agenda
• Signal manipulation (converter)
• Signal processing
• Signal transmission

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Signal Manipulation

• Resistance, current or voltage conversion
  Wheatstone bridge ? of a thermometer element
  or strain gauge into
• Inductance or capacitance to current or voltage
  conversion
• Displacement to current or voltage conversion
• Voltage-to-current conversion
• Current-to-voltage conversion
• Signal integration
• Signal addition
• Signal multiplication
• ADC/DAC, etc.

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The Wheatstone Bridge

• When Vo 0, the bridge is balance R2RTD
  R1R3
• When RTD is changed then

Example 1 A platinum resistance thermometer
element has a resistance of 100 ohm at 20oC and
is one of the arms of a Wheatstone bridge. The
bridge is balance at this temperature, all the
other arms also having a resistance of 100 ohm.
What will be the out-of-balance potential
difference when the temperature of the platinum
resistance thermometer element changes by 10oC
and causes its resistance to change by 3.9 ohm?
The bridge has a supply voltage of 6.0V.
Solution ?Vo (63.9)/(100100) 0.117V
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Other Converters
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Signal Processing

• Definition Signal processing signal to
  improve the quality of output
• Two kinds of signals digital analog
• Techniques
• Signal amplification output signal
• Signal attenuation (division) output
  signal
• Signal filtering unwanted signals
• Others linearization, bias removal.

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Signal Amplification

• Application low transducers output level
• Mechanical amplifiers small displacement
• ? bigger displacement
• Electronic amplifier (operational amplifier)
• Inverting amplifier Vo -(R2/R1)Vi
• Non-inverting amplifier Vo (R2/R1)1Vi

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Example 2

• Consider the inverting operational amplifier. The
  input resistance is R1 5kO and the feedback
  resistance is R2 100 kO and an input voltage of
  50mV is applied. Determine the gain of the
  amplifier and hence determine the output voltage.
• Solution
• Gain - R2/R1 - 100/5 -20
• Output Voltage gain input -20 50
  -1000mV

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Signal Attenuation

• Use a potentiometer
• Vo (Xw/XT)Vi
• Disadvantage low impedance ? OP-AMP with R1gtR2

Vo
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Example 3

• Determine the loading error of the voltage
  dividing circuit if Ei 10V, Rm 20,000 O,
  RT400 O, RWkRT, k 0.2
• Solution

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Signal Filtering

• Remove a certain band of frequencies
• Band of frequencies low-pass, high-pass,
  band-pass, band-stop filter ? cut-off frequency
• Z1, Z2 are the combinations of R, L, C

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Signal Filtering
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Digital Signal Processing

• High accuracy
• Longer processing time
• Expensive
• Hardware Computer Analog Interfaces
• Software perform signal processing
• Process
• the analog signal at ti,
• Convert to digital signals
• Signal amplification, attenuation, bias removal,
  linearization, digital filtering, etc.

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Signal Transmission

• Signal amplification if high signal-to-noise
  ratio, for the attenuation from signal wires
• Shielding signal from noise
• Current loop transmission varying voltage
  signals ? varying current signals
• Digital transmission voltage-to-frequency
  conversion to transfer in digital format
• Fiber-optic transmission convert electrical
  signals into a modulated light wave which is
  transmitted along a fiber-optic cable

Output transducer