powerpoint ® presentation chapter 21 semiconductor input devices section 21-1 thermistors section...
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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
Chapter 21 — Semiconductor Input Devices
ObjectivesSection 21-1 Thermistors
• Define thermistor and describe the classes of thermistors.
• Explain how to test thermistors.
Chapter 21 — Semiconductor Input Devices
A thermistor is a temperature-sensitive resistor whose resistance changes with a change in temperature.
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.
Chapter 21 — Semiconductor Input Devices
The hot and cold resistance of a thermistor can be checked with a DMM.
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?
Chapter 21 — Semiconductor Input Devices
ObjectivesSection 21-2
Photoconductive Cells• Describe photoconductive cells (photocells) and
give examples of how they are used.• Explain how to test photocells.
Chapter 21 — Semiconductor Input Devices
A photocell can be used to determine if the pilot light on a gas furnace is ON or OFF.
Chapter 21 — Semiconductor Input Devices
A photocell can be used to determine when a streetlight should turn on or off.
Chapter 21 — Semiconductor Input Devices
Humidity and contamination are the primary causes of photocell failure.
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?
Chapter 21 — Semiconductor Input Devices
ObjectivesSection 21-3
Photoconductive Diodes• Define photoconductive diode (photodiodes) and
explain how it operates.
Chapter 21 — Semiconductor Input Devices
A photodiode is a diode that is switched on and off by a light.
Chapter 21 — Semiconductor Input Devices
Photodiodes are used to position objects and turn machine functions on and off.
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?
Chapter 21 — Semiconductor Input Devices
ObjectivesSection 21-4
Pressure Sensors• Define and describe pressure sensors.• Explain how to test a pressure sensor.
Chapter 21 — Semiconductor Input Devices
A pressure sensor is a transducer that changes resistance with a corresponding change in pressure.
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.
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?
Chapter 21 — Semiconductor Input Devices
ObjectivesSection 21-5
Flow Detection Sensors• Define and describe flow detection sensors.
Chapter 21 — Semiconductor Input Devices
A solid-state flow detection sensor operates on the principle of thermal conductivity.
Chapter 21 — Semiconductor Input Devices
A flow detection sensor can be used to monitor product flow in a pipe.
Chapter 21 — Semiconductor Input Devices
A flow detection sensor can be used to monitor airflow in painting or welding exhaust system applications.
Chapter 21 — Semiconductor Input Devices
21-5 Checkpoint
1. In a thermal-type flow detection sensor, does the sensor’s 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?
Chapter 21 — Semiconductor Input Devices
ObjectivesSection 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.
Chapter 21 — Semiconductor Input Devices
A Hall generator is a thin strip of semiconductor material through which a constant control current is passed.
Chapter 21 — Semiconductor Input Devices
Hall effect sensors are available in a variety of packages for different applications.
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.
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).
Chapter 21 — Semiconductor Input Devices
Pendulum actuation is a combination of the head-on and slide-by actuation methods.
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.
Chapter 21 — Semiconductor Input Devices
A Hall effect sensor may be used for monitoring a remote conveyor operation.
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.
Chapter 21 — Semiconductor Input Devices
A Hall effect sensor can be used to monitor the level of liquid in a tank.
Chapter 21 — Semiconductor Input Devices
A door-interlock system can be designed using a Hall effect sensor, a magnetic card, and associated electronic circuitry.
Chapter 21 — Semiconductor Input Devices
Hall effect sensors are used in beverage gun applications because of their small size, sealed construction, and reliability.
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.
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.
Chapter 21 — Semiconductor Input Devices
Hall effect sensors may be used in a joystick application.
Chapter 21 — Semiconductor Input Devices
21-6 Checkpoint
1. Is the output of a Hall effect sensor of the digital (ON/OFF) type or analog (varying) type as a magnet moves closer to the sensor?
2. Can a magnet actuate a Hall effect sensor by moving in a sideways or straight manner?
Chapter 21 — Semiconductor Input Devices
ObjectivesSection 21-7
Proximity Sensors• Define proximity sensor and explain how it
operates.• Explain the difference between an inductive
proximity sensor and a capacitive proximity sensor.
Chapter 21 — Semiconductor Input Devices
Proximity sensors are available in an assortment of sizes and shapes to meet as many application requirements as possible.
Chapter 21 — Semiconductor Input Devices
Inductive proximity sensors use a magnetic field to detect the presence of a metallic target.
Chapter 21 — Semiconductor Input Devices
Capacitive proximity sensors use a capacitive field to detect the presence of a target.
Chapter 21 — Semiconductor Input Devices
Capacitive sensors work based on the dielectric constant of the material to be sensed.
Chapter 21 — Semiconductor Input Devices
21-7 Checkpoint
1. What type of proximity switch detects metallic objects?
2. What type of proximity switch detects any object that has a high dielectric constant?
Chapter 21 — Semiconductor Input Devices
ObjectivesSection 21-8
Ultrasonic Sensors• Define ultrasonic sensor and explain how it
operates.• Explain the difference between a direct mode
ultrasonic sensor and a diffused mode ultrasonic sensor.
Chapter 21 — Semiconductor Input Devices
Ultrasonic sensors detect objects by bouncing high-frequency sound waves off the objects.
Chapter 21 — Semiconductor Input Devices
An ultrasonic sensor used in the diffused mode can provide an analog output that varies linearly with the target’s distance from the sensor.
Chapter 21 — Semiconductor Input Devices
21-8 Checkpoint
1. What is the operating mode of an ultrasonic sensor called when the emitter sound waves travel in only one direction to the receiver?
2. What is the operating mode of an ultrasonic sensor called when the emitter sound waves travel in one direction to the detected object and bounces back in the opposite direction to the receiver?