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Questions and Answers
What type of output do discrete sensors provide?
What type of output do discrete sensors provide?
Which statement describes the term 'switch bounce'?
Which statement describes the term 'switch bounce'?
Which of the following sensors would be categorized as using ultrasonic technology?
Which of the following sensors would be categorized as using ultrasonic technology?
What hardware solution can be used to mitigate switch bounce?
What hardware solution can be used to mitigate switch bounce?
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What type of sensors give ON/OFF binary outputs?
What type of sensors give ON/OFF binary outputs?
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Magnetic sensors utilize which of the following phenomena?
Magnetic sensors utilize which of the following phenomena?
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What is the purpose of piezoelectric sensors?
What is the purpose of piezoelectric sensors?
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Which of the following best describes a resistive sensor?
Which of the following best describes a resistive sensor?
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What is a primary limitation of ultrasonic proximity sensors?
What is a primary limitation of ultrasonic proximity sensors?
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Which type of sensor is capable of sensing objects regardless of their color or reflectivity?
Which type of sensor is capable of sensing objects regardless of their color or reflectivity?
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Which of the following statements about the thru-beam optical sensor is true?
Which of the following statements about the thru-beam optical sensor is true?
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What kind of targets do ultrasonic proximity sensors sense best?
What kind of targets do ultrasonic proximity sensors sense best?
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Which characteristic differentiates optical sensors from inductive and capacitive sensors?
Which characteristic differentiates optical sensors from inductive and capacitive sensors?
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What adjustment can be made on ultrasonic proximity sensors with discrete outputs?
What adjustment can be made on ultrasonic proximity sensors with discrete outputs?
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Why do ultrasonic sensors struggle with liquids that have surface ripples?
Why do ultrasonic sensors struggle with liquids that have surface ripples?
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What is a significant advantage of optical sensors compared to other proximity sensors?
What is a significant advantage of optical sensors compared to other proximity sensors?
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What type of operation does a dark-off diffuse reflective optical sensor perform when a target object is present?
What type of operation does a dark-off diffuse reflective optical sensor perform when a target object is present?
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How does a retro-reflective optical sensor differ from a diffuse reflective sensor?
How does a retro-reflective optical sensor differ from a diffuse reflective sensor?
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What principle does the bi-metallic switch operate on?
What principle does the bi-metallic switch operate on?
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In the operation of a bi-metallic switch, which metal expands more significantly when temperature increases?
In the operation of a bi-metallic switch, which metal expands more significantly when temperature increases?
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What type of materials can a capacitive proximity sensor detect?
What type of materials can a capacitive proximity sensor detect?
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What is the main advantage of a retro-reflective optical sensor over a thru-beam optical sensor?
What is the main advantage of a retro-reflective optical sensor over a thru-beam optical sensor?
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What triggers the reeds in a basic reed switch to close?
What triggers the reeds in a basic reed switch to close?
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What happens to the bi-metallic strip in a bi-metallic switch as temperature rises?
What happens to the bi-metallic strip in a bi-metallic switch as temperature rises?
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When a target object is not present, what state does a dark-off diffuse reflective optical sensor output?
When a target object is not present, what state does a dark-off diffuse reflective optical sensor output?
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How does an ultrasonic proximity sensor detect a target?
How does an ultrasonic proximity sensor detect a target?
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What occurs immediately after an ultrasonic sensor transmits a ping?
What occurs immediately after an ultrasonic sensor transmits a ping?
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Which statement about the construction of a bi-metallic switch is correct?
Which statement about the construction of a bi-metallic switch is correct?
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What is the 'deadband' in the context of ultrasonic proximity sensors?
What is the 'deadband' in the context of ultrasonic proximity sensors?
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What happens to the output signal of an inductive proximity sensor when a metallic object moves closer to it?
What happens to the output signal of an inductive proximity sensor when a metallic object moves closer to it?
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What principle does the ultrasonic proximity sensor use to operate?
What principle does the ultrasonic proximity sensor use to operate?
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Which of the following materials can inductive proximity sensors detect?
Which of the following materials can inductive proximity sensors detect?
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What is the principle behind the operation of inductive proximity sensors?
What is the principle behind the operation of inductive proximity sensors?
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Why might an ultrasonic sensor fail to detect a close target?
Why might an ultrasonic sensor fail to detect a close target?
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What occurs in the oscillator circuit when a metallic target is in proximity?
What occurs in the oscillator circuit when a metallic target is in proximity?
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Which of the following is a limitation of ultrasonic proximity sensors?
Which of the following is a limitation of ultrasonic proximity sensors?
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When does the trigger circuit activate in an inductive proximity sensor?
When does the trigger circuit activate in an inductive proximity sensor?
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What is the function of the non-metallic face of an inductive proximity sensor?
What is the function of the non-metallic face of an inductive proximity sensor?
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What happens to the output of an inductive proximity sensor when it senses air?
What happens to the output of an inductive proximity sensor when it senses air?
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How do capacitive proximity sensors differ from inductive ones?
How do capacitive proximity sensors differ from inductive ones?
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Study Notes
Mechatronics Systems (MCT 317) - Lecture 06: Switches and Proximity Sensors
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Sensor Technologies:
- Capacitive
- Resistive
- Magnetic
- Piezoelectric
- Strain gauges
- Piezoresistive
- Optical
- Ultrasonic
- Etc.
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Types of Sensors:
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Fundamental Categories:
- Discrete (Digital, Logic, Bang-Bang): Provides a single logical output (0 or 1). Examples include thermostats controlling heating/cooling.
- Proportional (Analog): Provides a continuous output related to the measured value.
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Discrete Position Sensors: Provide a single logical output (0 or 1).
- Example: A thermostat that controls heating/cooling, outputting a 0 when the temperature is below the setpoint and a 1 when it's above.
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Discrete (Logic) Sensors:
- Include mechanical limit switches or microswitches.
- Activation causes electrical contacts to either:
- Break (Normally Closed - NC switch)
- Make (Normally Open - NO switch)
- Or both NC and NO.
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Limit and Micro-switches: Various types exist for different applications and forces.
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Standard Basic Switches:
- Lever: Very low force, slow cams and slides.
- Roller lever: Very low force, fast moving cams.
- Overtravel Plunger: In-line applications needing additional overtravel.
- Panel-mount Plunger: Heavy-duty in-line applications or slow cams.
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Switch Contact Configurations:
- Single pole, single throw (SPST): Normally Open (NO) or Normally Closed (NC).
- Single pole, double throw (SPDT).
- Double pole, double throw (DPDT).
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Switch Bounce Problem:
- Mechanical switches can bounce when closing or opening contacts.
- This can appear as multiple separate switch operations to a microprocessor. Delays and time periods.
- Typically lasts around 20 milliseconds.
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Debouncing Circuits:
- Hardware solution to switch bounce: Utilizes flip-flops and/or RC filters.
- RC filter debouncer. This is a circuit constructed using a resistor and a capacitor.
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Magnetic Sensors:
- Utilize magnetic phenomena (Inductance/Inductive sensors, Reluctance, Eddy currents) to measure displacement.
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Inductive Sensors:
- Inductive displacement sensor.
- I = V/ωL (where V is voltage, ω is angular velocity, and L is inductance)
- Output-current/displacement characteristic needs calibration.
- Applications are limited to metal targets given operation principle.
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Inductive Proximity Sensors: Detect the presence of metal objects.
- Vary the inductance of the coil based on the metal presence
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Inductive Proximity Sensor Internal Components: (See diagram on page 14 for details)
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Inductive Proximity Sensor Signals:
- Sensor provides an "off" signal when sensing a non-metallic material and changes to "on" when a metal object enters the sensing area and causes a decrease in the amplitude of the oscillator.
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Capacitive Sensors:
- Consists of two parallel metal plates
- Dielectric between the plates is either air or some other medium.
- C= ε₀εr A/d (Where C is capacitance, ε₀ is the absolute permitivity of free space, εr is the relative permitivity of the dielectric material, A is the area of the plates, and d is the distance between the plates.)
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Capacitive Proximity Sensors: Detect the presence of objects, both metallic and non-metallic.
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Capacitive Proximity Sensor - Internal Components (See diagram on page 19 for details)
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Reed Switch Principle:
- Small glass tube with soft iron reeds.
- Reeds become magnetic in a magnetic field and pull together.
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Ultrasonic Sensors:
- Measure distance using time-of-flight principle. A ping is sent, and the echo is analyzed to figure out the distance to the target.
- Has a cone-shaped dispersion of sound waves.
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Ultrasonic Sensing: High frequency (200kHz) sound waves reflecting for detection. (See diagrams, page 22 for diagrams).
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Ultrasonic Sensors Limitations: Has a sensing range, Cone-shaped, "blind" period (no detection when measuring a flashbulb)
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Ultrasonic Proximity Sensor Useable Sensing Area: Area to measure distance.
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Discrete (Logic) Ultrasonic Proximity Sensor:
- Switch point adjustment to set target distance
- Analog outputs available for measuring distances.
- Not effective with liquids, soft materials, poor with surface ripples or waves.
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Optical Sensors:
- Use light to detect objects (opaque objects regardless of color); large ranges; works in a vacuum.
- Uses focused beams (lenses to avoid crosstalk).
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Thru-Beam (Interrupted) Proximity Sensor:
- Uses emitter and receivers on opposite sides of the target area. Blocks light for detection.
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Diffuse Reflective Proximity Sensor:
- Emitter and receiver in the same sensor. Sensing using light reflection.
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Retro-reflective (Reflex) Proximity Sensor:
- Emitter and receiver in a single unit. Uses a reflector to bounce the light back to the receiver.
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Optical Proximity Switches: Examples: automatic door openers, case sorting (by size), production counting
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Bi-Metallic Switch:
- Discrete switch based on different thermal expansion coefficients of two metals.
- Changes in temperature cause the strip to bend, activating contacts.
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Bi-Metallic Switch Internal Components: Showing how the different expansion coefficients work in each switch to control temperature.
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Presentation Conclusion:
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Description
Explore the fascinating world of switches and proximity sensors in this lecture for Mechatronics Systems (MCT 317). Learn about various sensor technologies, their fundamental categories, and specific types of sensors, including discrete and proportional options. This quiz will test your understanding of how these sensors function and their applications in real-world scenarios.
