The length of time from the application of an input until the output to respond

The length of time from the application of an input

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The length of time from the application of an input until the output to respond and change Example: EV3 Touch sensor 23 time(sec) x(mm) time(sec) touchsensor x* 0 1 t* (deadtime) * * 1, 0, 0 x x f x x x T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved
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Static and dynamics characteristics A&H 4th: Chapter 4.7 – 4.9 Bolton 6th: Chapter 2, 19.3 24 T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved
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Static and Dynamic Characteristics Response time of different thermometers Infrared thermometer Fluke 561 Infrared Thermometer Response time: <500 milliseconds Resolution: 0.1 °C Cost: $199.00 Analog thermometer Fridge / Freezer Thermometer Response time: ~ 60 seconds Resolution: 1 °C Cost: $4.00 25 - model/3563941?PubID=UX&persist=true&ip=no&gclid=Cj0KCQjwv_fKBRCGARIsAL6R6e igQ9nzpWPPFuCwITG9FzwhNY73mLAn06d8K3b3si-78pWAl47CRGwaArSuEALw_wcB - fridge-freezer-thermometer-with-hook.html T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved
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26 Time response of a sensor The first order differential equation is: Where u ( t ) is the input, y ( t ) is the output of the system. T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved ( ) u t t 1 0 t Input ܽ ݀ݕሺݐሻ ݀ݐ ൅ ܽ ݕ ݐ ൌ ܾ ݑሺݐሻ ݕ ݐ ܾ ܽ 1 െ ݁ ି , ݐ ൒ ݐ ݑ ݐ ൌ ቊ 0, ݐ ൒ ݐ 1, 0 ൑ ݐ ൏ ݐ SteadyStateGainܩ ௦௦ ܾ ܽ , Time Constant ߬ ൌ ( ) y t t SS G 0 t Output
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27 Time measures Time Constant Response Time Rise Time Settling Time T02_Time_Measure_eg.slx T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved
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28 Example: Time measure Consider the following data which indicates how a thermometer reading changed with time by plunging into a liquid at time t = 0. What is the 95% response time? Answer: 20 25 30 35 40 45 50 55 60 0 100 200 300 400 t (sec) T (C) The steady-state value is 55°C and so, since 95% of 55 is 53.25°C: 0.95 20 0.95 55 20 53.25 T Time (s) 0 30 60 90 120 150 180 210 240 270 300 330 360 Temp ( O C) 20 28 34 39 43 46 49 51 53 54 55 55 55 the 95% estimated response time is about 247.5 s. T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved
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Sensor selection 29 T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved
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30 Sensor Selection Considerations The size of the displacement Example: 1mm or 10 m Whether the displacement is linear or angular Example: Distance readings from Ultrasonic Sensor (linear) or Angular Velocity readings from EV3 Motors (angular) The resolution required Example: EV3 Color (light) Sensor: Raw (0-1023) or Normalized (0-100) The accuracy required Example: 1cm (Ultrasonic Sensor for the course Project), 1 nm (nanotechnology) or 10 m (astronomy) What material the measured object is made of Example: reflective surface (use Color Sensor to detect the Black Tape, use Ultrasonic Sensor to detect obstacles) or magnetic (use Hall effect) T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved
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31 Example: of Sensor Types Non-contact sensor Example: Proximity sensors Contact sensor Example: potentiometer sensor T02 - Sensors © Mo-Yuen Chow, NC State University, All Rights Reserved
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