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Electrical Instrumentation

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Electrical instrumentation is the process of acquiring data about one or more ... The gain of the amplifier is set so that the voltage falls between lower and ... – PowerPoint PPT presentation

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Title: Electrical Instrumentation


1
Electrical Instrumentation
2
Electrical Instrumentation
  • Electrical instrumentation is the process of
    acquiring data about one or more physical
    quantities of interest using electrical sensors
    and instruments.
  • This data may be used for diagnostics, analysis,
    design, or to control a system.

3
Instrumentation Examples
  • Every engineering discipline uses electrical
    instrumentation to collect and analyze data.
  • The following examples are illustrative of the
    different types of sensors and instrumentation
    that different engineering disciplines use.

4
Strain Measurements
Strain gauge
5
Non-destructive Testing
Ultrasound transducer
6
Automotive Sensors
Oxygen Sensor
Accelerometer
Airflow Sensor
Oil Pressure
Water Temperature
CO Sensor
7
Biomedical
Ultrasound Transducer
8
What other examples can you think of?
9
A Typical Instrumentation System
A/D Converter
Sensor
Computer
10
Instrumentation System
  • Sensor-converts the measured value into an
    electrically useful value.
  • Amplifier-conditions the signal from the
    sensor.
  • A/D Converter-converts the signal into a digital
    format.
  • Computer-processes, displays, and records the
    signal.

11
Sensor
  • The output of a sensor is proportional to the
    quantity of interest.
  • The sensor output may be a
  • voltage or current (temperature, pressure)
  • resistance (strain gauge)
  • frequency (accelerometer)

12
Amplifier
  • The output of the amplifier is (usually) a
    voltage.
  • The gain of the amplifier is set so that the
    voltage falls between lower and upper limits (for
    example, -10V to 10V).

13
A/D Converter
  • Analog-to-digital conversion consists of two
    operations
  • Sampling measuring the voltage signal at equally
    spaced points in time.
  • Quantization approximating a voltage using 8 or
    16 bits.

14
Instrumentation Issues
  • Noise
  • Signal bandwidth
  • Sampling
  • Amplifier characteristics
  • Feedback
  • Real-time processing
  • Control systems

15
Noise
Signal
Signal Noise
16
Sources of Noise
  • Thermal noise caused by the random motion of
    charged particles in the sensor and the
    amplifier.
  • Electromagnetic noise from electrical equipment
    (e.g. computers) or communication devices.
  • Shot noise from quantum mechanical events.

17
Effects of Noise
  • Reduces accuracy and repeatability of
    measurements.
  • Introduces distortion in sound signals.
  • Introduces errors in control systems.

18
What to Do?
  • How can we eliminate or reduce the undesirable
    effects of noise?
  • Grounding/shielding electrical connections
  • Filtering (smoothing)
  • Averaging several measurements

19
Signal Bandwidth
  • Conceptually, bandwidth is related to the rate at
    which a signal changes

Low BW
High BW
20
Bandwidth and Sampling
  • A higher bandwidth requires more samples/second

Low BW
High BW
21
Bandwidth Limitations
  • Every component in the instrumentation system has
    bandwidth limitations
  • Sensors do not respond immediately to changes in
    the environment.
  • The amplifier output does not change immediately
    in response to changes in the input.
  • The A/D converter sampling rate is limited.

22
Effects of BW Limitations
Sensor Output
Amplifier Output
23
Amplifier Characteristics
  • Amplifiers are characterized in terms of
    attributes such as
  • Gain
  • Bandwidth and/or frequency response
  • Linearity
  • Harmonic distortion
  • Input and output impedance

24
Op Amps
  • One commonly used type of amplifier is the
    Operational Amplifier (OpAmp).
  • Op Amps have differential inputs output voltage
    is the amplified difference of two input
    voltages.
  • Op Amps have very large gains (gt103).

25
Op Amps (cont.)
  • Most op amp circuits use negative feedback.
  • Op amp circuits can be designed to
  • Provide voltage gain or attenuation.
  • Convert current to voltage.
  • Integrate or differentiate.
  • Filter out noise or interference.

26
Feedback
  • Often, sensors measure quantities associated with
    systems. The sensor output is used to control
    the system in a desired manner.

27
Example Industrial Process Control
  • In many manufacturing processes (integrated
    circuits, for examle) temperatures must be
    closely controlled.
  • Feedback can be used to maintain a constant
    temperature.

28
Temperature Control
Furnace and Material
Desired Temperature
Control System
Temperature Sensor
  • The Control System sets the current supplied to
    the heating elements in the furnace to keep the
    material temperature at the desired value.

29
A car cruise control is a feedback system. How
does it work?
30
Benefits of Feedback
  • Provides stability with respect to changes in
    system parameter values.
  • Helps to obtain a (nearly) linear response from
    non-linear components.
  • Can be used to change the characteristics of a
    system under control.
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