IT 435 Digital Instumentation and Control

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IT 435 Digital Instumentation and Control

• Week 2

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Describe how diodes are used in electronic
circuitry

• Directionally sensitive
• Two leads
• Band indicates flow direction ( to -)
• Characteristic curve
• Breakdown voltage
• Reversal permanently damages diode

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Describe how diodes are used in electronic
circuitry

• Zener Diode
• Controlled breakdown - regulates voltage
• Self healing

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Describe npn and pnp transistor operation

• Three leads

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Describe npn and pnp transistor operation

• Like a cathode tube
• Used to turn on devices
• FET - Field Effect Transistor (MOSFET)
• Modern transistors can handle much more power
  (current flow)

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Describe the function of a silicon controlled
rectifier
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Describe the function of a silicon controlled
rectifier

• SCR - Useful device for rectifying AC
• Converting it to DC
• Blocks lower half
• Can invert signal
• Can be controlled to pass a limited amount of
  electricity
• Modern capable of high power
• Extremely useful for controlling modern motors

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Types of thermal transducers and sensors

• Thermistor
• Temperature range - 0 to 100 degrees C
• Semiconductor based

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Types of thermal transducers and sensors

• Thermistor
• Non-linear
• Generally requires interpreter (computer)

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Types of thermal transducers and sensors

• Resistance temperature device
• Temperature range - -200 to 700 degrees C

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Types of thermal transducers and sensors

• Resistance temperature device
• Linear - Resistance proportional to temperature
• Generally made of platinum - expensive
• Low signal strength
• Requires accurate instrument to measure

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Types of thermal transducers and sensors

• Thermocouples
• Seebeck effect
• Dissimilar metals when heated produce voltage
• Temperature range- 1000 to 2200 degrees F
• Linear - current proportional to temperature

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Types of thermal transducers and sensors

• Infrared pyrometer
• Optical device detects radiation of a heat source
• No physical contact
• Temperatures - 2000 F and greater

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Force, Pressure and strain measurement

• Strain gages
• Stress
• Pressure
• Deflection

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Capacitance Measurement

• Electric charge related to space between objects
• Elevators
• Non-metallic processes

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Types of optical transducers and sensors

• Opposed - through beam
• Transmitter and receiver located separately

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Types of optical transducers and sensors

• Retroreflective
• Beam reflected
• Some energy loss
• Less range

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Types of optical transducers and sensors

• Diffuse
• Depends on reflection from the object

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Types of magnetic transducers and sensors

• Induction transducers - Magnets and coils
• Variable reluctance - coils and metal
• Tooth pick-ups
• Hall effect
• semiconductor

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Proximity Sensor

• Altech

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Types of electromechanical transducers and sensors

• Linear variable differential transducer
• LVDT
• Distance, motion
• Solenoid construction

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Types of electromechanical transducers and sensors

• Linear variable differential transducer

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Choosing the proper sensor for an application

• Consideration of limitations of use
• Degree of accuracy
• Environment
• Redundancy

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Electric Motor Encoders
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Gray Code