PowerPoint ® Presentation Chapter 21 Semiconductor Input Devices Section 21-1 Thermistors Section 21-2 Photoconductive Cells Section 21-3 Photoconductive

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  • Slide 1
  • PowerPoint Presentation Chapter 21 Semiconductor Input Devices Section 21-1 Thermistors Section 21-2 Photoconductive Cells Section 21-3 Photoconductive Diodes Section 21-4 Pressure Sensors Section 21-5 Flow Detection Sensors Section 21-6 Hall Effect Sensors Section 21-7 Proximity Sensors Section 21-8 Ultrasonic Sensors
  • Slide 2
  • Chapter 21 Semiconductor Input Devices Objectives Section 21-1 Thermistors Define thermistor and describe the classes of thermistors. Explain how to test thermistors. Define thermistor and describe the classes of thermistors. Explain how to test thermistors.
  • Slide 3
  • Chapter 21 Semiconductor Input Devices A thermistor is a temperature-sensitive resistor whose resistance changes with a change in temperature.
  • Slide 4
  • Chapter 21 Semiconductor Input Devices In the presence of fire, the increase in temperature lowers the resistance of an NTC thermistor, which increases current and activates an alarm.
  • Slide 5
  • Chapter 21 Semiconductor Input Devices The hot and cold resistance of a thermistor can be checked with a DMM.
  • Slide 6
  • Chapter 21 Semiconductor Input Devices 21-1 Checkpoint 1.What happens to the resistance of a PTC thermistor when it is heated? 2.What happens to the resistance of an NTC thermistor when it is heated? 3.What is the most commonly used thermistor type? 1.What happens to the resistance of a PTC thermistor when it is heated? 2.What happens to the resistance of an NTC thermistor when it is heated? 3.What is the most commonly used thermistor type?
  • Slide 7
  • Chapter 21 Semiconductor Input Devices Objectives Section 21-2 Photoconductive Cells Describe photoconductive cells (photocells) and give examples of how they are used. Explain how to test photocells. Describe photoconductive cells (photocells) and give examples of how they are used. Explain how to test photocells.
  • Slide 8
  • Chapter 21 Semiconductor Input Devices A photocell can be used to determine if the pilot light on a gas furnace is ON or OFF.
  • Slide 9
  • Chapter 21 Semiconductor Input Devices A photocell can be used to determine when a streetlight should turn on or off.
  • Slide 10
  • Chapter 21 Semiconductor Input Devices Humidity and contamination are the primary causes of photocell failure.
  • Slide 11
  • Chapter 21 Semiconductor Input Devices 21-2 Checkpoint 1.What happens to the resistance of a photoconductive cell as light on it increases? 2.What happens to the current flowing through a photoconductive cell as light on it increases? 1.What happens to the resistance of a photoconductive cell as light on it increases? 2.What happens to the current flowing through a photoconductive cell as light on it increases?
  • Slide 12
  • Chapter 21 Semiconductor Input Devices Objectives Section 21-3 Photoconductive Diodes Define photoconductive diode (photodiodes) and explain how it operates.
  • Slide 13
  • Chapter 21 Semiconductor Input Devices A photodiode is a diode that is switched on and off by a light.
  • Slide 14
  • Chapter 21 Semiconductor Input Devices Photodiodes are used to position objects and turn machine functions on and off.
  • Slide 15
  • Chapter 21 Semiconductor Input Devices 21-3 Checkpoint 1.What happens to the resistance of a photodiode when light is shining on it? 2.What happens to the current flowing through a photodiode when light is shining on it? 1.What happens to the resistance of a photodiode when light is shining on it? 2.What happens to the current flowing through a photodiode when light is shining on it?
  • Slide 16
  • Chapter 21 Semiconductor Input Devices Objectives Section 21-4 Pressure Sensors Define and describe pressure sensors. Explain how to test a pressure sensor. Define and describe pressure sensors. Explain how to test a pressure sensor.
  • Slide 17
  • Chapter 21 Semiconductor Input Devices A pressure sensor is a transducer that changes resistance with a corresponding change in pressure.
  • Slide 18
  • Chapter 21 Semiconductor Input Devices Pressure sensors are tested by checking the voltage or current output and then comparing the value to the manufacturer specification sheets.
  • Slide 19
  • Chapter 21 Semiconductor Input Devices 21-4 Checkpoint 1.If a pressure sensor that is rated to output 0 VDC to 10 VDC with a specified pressure operating range of 0 psi to 500 psi outputs 2 VDC, is it working properly according to manufacturer specifications? 2.If a pressure sensor that is rated to output 4 mA to 20 mA DC with a specified pressure operating range of 0 psi to 500 psi outputs 2.5 mA, is the pressure sensor working properly according to manufacturer specifications? 1.If a pressure sensor that is rated to output 0 VDC to 10 VDC with a specified pressure operating range of 0 psi to 500 psi outputs 2 VDC, is it working properly according to manufacturer specifications? 2.If a pressure sensor that is rated to output 4 mA to 20 mA DC with a specified pressure operating range of 0 psi to 500 psi outputs 2.5 mA, is the pressure sensor working properly according to manufacturer specifications?
  • Slide 20
  • Chapter 21 Semiconductor Input Devices Objectives Section 21-5 Flow Detection Sensors Define and describe flow detection sensors.
  • Slide 21
  • Chapter 21 Semiconductor Input Devices A solid-state flow detection sensor operates on the principle of thermal conductivity.
  • Slide 22
  • Chapter 21 Semiconductor Input Devices A flow detection sensor can be used to monitor product flow in a pipe.
  • Slide 23
  • Chapter 21 Semiconductor Input Devices A flow detection sensor can be used to monitor airflow in painting or welding exhaust system applications.
  • Slide 24
  • Chapter 21 Semiconductor Input Devices 21-5 Checkpoint 1.In a thermal-type flow detection sensor, does the sensors thermistor produce higher or lower electrical signal when there is no flow? 2.Is a thermal-type flow detection sensor a fast- acting or slow-acting change detection type? 1.In a thermal-type flow detection sensor, does the sensors thermistor produce higher or lower electrical signal when there is no flow? 2.Is a thermal-type flow detection sensor a fast- acting or slow-acting change detection type?
  • Slide 25
  • Chapter 21 Semiconductor Input Devices Objectives Section 21-6 Hall Effect Sensors Define Hall effect sensor and explain the Hall effect. Explain how Hall effect sensors operate. Explain how Hall effect sensors may be actuated. Describe Hall effect sensor applications. Define Hall effect sensor and explain the Hall effect. Explain how Hall effect sensors operate. Explain how Hall effect sensors may be actuated. Describe Hall effect sensor applications.
  • Slide 26
  • Chapter 21 Semiconductor Input Devices A Hall generator is a thin strip of semiconductor material through which a constant control current is passed.
  • Slide 27
  • Chapter 21 Semiconductor Input Devices Hall effect sensors are available in a variety of packages for different applications.
  • Slide 28
  • Chapter 21 Semiconductor Input Devices In head-on actuation, a magnet is oriented perpendicular to the surface of the sensor and is usually centered over the point of maximum sensitivity.
  • Slide 29
  • Chapter 21 Semiconductor Input Devices In slide-by actuation, a magnet is moved across the face of a Hall effect sensor at a constant distance (gap).
  • Slide 30
  • Chapter 21 Semiconductor Input Devices Pendulum actuation is a combination of the head-on and slide-by actuation methods.
  • Slide 31
  • Chapter 21 Semiconductor Input Devices In vane actuation, an iron vane shunts or redirects the magnetic field in the air gap away from the Hall effect sensor.
  • Slide 32
  • Chapter 21 Semiconductor Input Devices A Hall effect sensor may be used for monitoring a remote conveyor operation.
  • Slide 33
  • Chapter 21 Semiconductor Input Devices Each change in polarity results in an output from a Hall effect sensor used in a shaft speed sensor application.
  • Slide 34
  • Chapter 21 Semiconductor Input Devices A Hall effect sensor can be used to monitor the level of liquid in a tank.
  • Slide 35
  • Chapter 21 Semiconductor Input Devices A door-interlock system can be designed using a Hall effect sensor, a magnetic card, and associated electronic circuitry.
  • Slide 36
  • Chapter 21 Semiconductor Input Devices Hall effect sensors are used in beverage gun applications because of their small size, sealed construction, and reliability.
  • Slide 37
  • Chapter 21 Semiconductor Input Devices Length measurement can be accomplished by mounting a disk with two notches on the extension of a motor drive shaft.
  • Slide 38
  • Chapter 21 Semiconductor Input Devices Hall effect sensors may be installed in the base of a machine to indicate the level or degree of tilt.
  • Slide 39
  • Chapter 21 Semiconductor Input Devices Hall effect sensors may be used in a joystick applic