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Bài Giảng Môn Học Thực hành Cảm Biến

Chia sẻ: Đặng Vũ Thanh Hùng | Ngày: | Loại File: PDF | Số trang:16

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Inductive proximity sensors are widely used in various applications to detect metal devices. They consist of an oscillator, trigger, and switching amplifier. If a metal object enters the electromagnetic field of the oscillator coil, eddy currents are induced in this coil which change the amplitude of oscillation, which causes the trigger stage to trip and the semiconductor output stage to switch.

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Nội dung Text: Bài Giảng Môn Học Thực hành Cảm Biến

  1. Thực hành cảm biến TRƯỜNG ĐẠI HỌC NHA TRANG KHOA CƠ KHÍ BỘ MÔN CƠ ĐIỆN TỬ ------ Nguyễn Văn Định BÀI GIẢNG MÔN HỌC THỰC HÀNH CẢM BIẾN (Lưu hành nội bộ) Nha Trang, năm 2009 1
  2. Thực hành cảm biến 1. Mục đích Giúp sinh viên cách đo đạc, thu thập và hiển thị giá trị của một số loại cảm biến thông dụng. 2. Yêu cầu Tham gia đầy đủ các buổi học lý thuyết và thực hành. 3. Nội dung môn học Sử dụng bộ thí nghiệm KL-620 để đo đạc và lập trình hiển thị. - Cảm biến tiệm cận (Proximity) - Cảm biến nhiệt độ (Temp PT-100) - Cảm biến góc quay (Rotation Angle) - Cảm biến rung (Vibration) - Cảm biến hồng ngoại (Infrared) - Cảm biến quang (CDS) 2
  3. Thực hành cảm biến 1.1. Cảm biến tiệm cận Proximity Sensor Structure: Symbol: (Equipment Circuit) Detect Head VCC Output GND LED: Indicator Oscillator Trigger Switching Amplifier Inductive proximity sensors are widely used in various applications to detect metal devices. They consist of an oscillator, trigger, and switching amplifier. If a metal object enters the electromagnetic field of the oscillator coil, eddy currents are induced in this coil which change the amplitude of oscillation, which causes the trigger stage to trip and the semiconductor output stage to switch. Circuit Explanation When no metallic object approach to the detecting head: Vo = High  Vo22 = Low  Q1 OFF  Buzzer OFF 3
  4. Thực hành cảm biến When a metallic object approach to the detecting head: Vo = LOW  Vo22 = High  Q1 ON  Buzzer ON Experiment Procedure: 1. Insert proximity sensor to 3 pin module socket. 2. Power on the module 3. Use different type of object to approach to the detecting head and observe the result.  _______________________________________________________________________ Tài liệu trên được đăng bởi Đặng Vũ Thanh Hùng (Sinh Viên Trường Cao Đẳng Kĩ Thuật Cao Thắng //// >Khóa< __2010__) Thuộc: >KhoaNgànhLớpMSSV
  5. Thực hành cảm biến 1.2. Cảm biến nhiệt độ: Temperature (PT100) Sensor Symbol: Structure: Stainless-steel protection tube (Platinum wired wound inside) B’ Voltage Out B’ B=B’ A A B PT-100 is one form of the RTD (Resistance Temperature Detector). It is made of the platinum wire and has the resistance of 100 ohm at 00C. The resistance vs. temperature characteristic of PT-100 can be expressed as: RT = 100 (1+0.00392T) If constant current I of 2.55mA flow through PT-100 VB’ = I x RT = (255+T)mV Circuit Explanation: 5
  6. Thực hành cảm biến • VR2 is used to control the constant current source to 2.25mV • U1 is non-inverting amplifier  V16= (2550+10T) mV • U2 is differential amplifier • U3 is voltage follower  Adjust VR14 to control Vf1 (offset of U2) So if Vf1 = 2550mV  Vo27 = 100T mV  Conversion Ratio = 100mV / 0C • Experiment Procedure: In this exercise, you need to prepare a thermometer (mercury) for calibration. 1. Using thermometer to record the current room temperature (T). ? 2. Connect 2 lead wires (white) to B and B’, and lead wire (red) to A. 3. Power on the module. 4. Adjust VR2 until VB’ = (255+T)mV ? 5. Adjust VR14 until Vo27 is equal to T/10 V (Calibration complete) ? 6. Put both PT-100 and the mercury thermometer inside hot water. 7. What is the value shown on the mercury thermometer? ? 8. What is the output voltage of Vo27? ? 9. Put both PT-100 and the mercury thermometer inside cold water. 6
  7. Thực hành cảm biến 10. What is the value shown on the mercury thermometer? ? 11. What is the output voltage of Vo27? ? 12. What’s the difference between AD590 and PT100 temperature sensor? ? 7
  8. Thực hành cảm biến 1.3. Cảm biến góc quay Rotation Angle Sensor Symbol: Structure: Plastic Housing Knob Excitation Vout Voltage CCW Output CW (sliding connection) Sometimes called potentiometers, voltage dividers or variable resistors, the precision potentiometric position transducers are widely used in measuring linear distance, angles or rotations in production equipment. It is a three terminal resistor where the position of the sliding connection is user adjustable via a knob. The sensor used in this experiment is a multi-turn potentiometer (10 turns) with an attached reel of wire turning against a spring. Circuit Explanation: 8
  9. Thực hành cảm biến • U1 (Buffer Amplifier) provides a precision reference voltage at Vf1. • U2 (Buffer Amplifier) transfers the voltage from U2pin3 to U2pin6. • U4 (Buffer Amplifier) provides fix voltage (adjusted by VR7) at U4pin6 to control the current flow through feedback loop to obtain a stable output at Vo31. Experiment Procedure: 1. Power on the module 2. Adjust variable resistor VR7 to center for initial position. 3. Rotate the potentiometer from most CCW to most CW position. How many turns is built in the potentiometer? ? 4. How many degrees you have rotate in step 2? ? 5. Fix the potentiometer at 36000 Adjust the variable resistor VR2 until Vo31 is equal to 3.600V. 6. Rotate the potentiometer in CCW direction for 5 turns. Adjust the variable resistor VR7 until Vo31 is equal to 1.800V. 7. Measure and record the output voltage Vo31 for each following turn values. 1/2/3/4/5/6/7/8/9/10 turns ? 9
  10. Thực hành cảm biến 1.4. Cảm biến rung Vibration Switch Structure: Symbol: Housing Contact: to spring Contact to metal The vibration switch is normally open with vibration springs. When a vibration occurred, the switch changes to close state and the switch turns ON. Circuit Explanation: 10
  11. Thực hành cảm biến When vibration switch is OFF : 555 Timer (U2) OFF  no output at Vo10  Buzzer OFF When vibration switch is ON : 555 Timer (U2) ON  pulse output at Vo10  Buzzer ON Experiment Procedure: 1. Power on the module. 2. What is the status of the buzzer? 3. Knock the sensor from side, what is the status of the buzzer? 4. Knock the sensor from top, what is the status of the buzzer? 11
  12. Thực hành cảm biến 1.5. Cảm biến hồng ngoại Infrared Sensor Transmitter Receiver Anode Transmitter Receiver (Infrared Emitting Diode) (Photodiode) Cathode Infrared emits infrared radiation which is focused by a plastic lens into a narrow beam. The emitting beam of an IR LED is generally proportional to the magnitude of the forward current (forward biased). The beam is modulated i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current for further processing. Circuit Explanation: Vout_U3 Vout_U2 12
  13. Thực hành cảm biến U2: Inverting amplifier, Gain = ~1000 U3: differential amplifier, Gain = ~ 22 U4: Comparator, If V+ > V-  output = 12V || If V->V+  output = -12V Use VR2 to adjusted the output frequency f of the 555 Timer  Q1 switches ON and OFF  Infrared TX emits ON and OFF  If no object blocks between TX and RX  Infrared RX receives ON and OFF  weak pulse signal input to U2  strong pulse signal  Vpp = 12V, frequency = f) output at Vout_U2  At resonant frequency  VLc obtain maximum Vpp  signal amplify again though U3  CR1, C5, R13 converts the AC signal into DC signal at U4 pin3  If U4 pin3 > U4 pin2  Vo17 outputs high potential Experiment Procedure: 1. Power on the module 2. Use oscilloscope to observe the voltage at VLC and adjust the variable resistor VR2 until Vout_U2 obtain the maximum peak-to-peak voltage. 3. Adjust VR3 until U3 pin3 is 0.3V lower than VLC  4. Record the voltage at U4 pin2 and U4 pin3  5. Block an object between the sensor, what is the voltage at U4 pin3?  6. What is the value of Vo17 when nothing block the sensor?  7. What is the value of Vo17 when the sensor is blocked by an object?  8. What is the current frequency of the 555 Timer output?  13
  14. Thực hành cảm biến 1.6. Cảm biến quang Infrared Sensor Structure: Symbol: CaDmium Sulphide (Orange part) Lead Wires CaDmium Sulphide (CDS) cells, sometimes called photoresistors or photoconductive cells, rely on the material's ability to vary its resistance according to the amount of light striking the cell. The more light that strikes the cell, the lower the resistance. Circuit Explanation: 14
  15. Thực hành cảm biến When light strikes the CDS: Sensor resistance  Vin  Q1 (NPN) ON  Q2 (PNP) ON  Vo23 High  LED1 ON When no light strikes the CDS: Sensor resistance  Vin  Q1 (NPN) OFF  Q2 (PNP) OFF  Vo23 LOW  LED1 OFF Experiment Procedure: 1. Power on the module 2. Block the CDS and adjust variable resistor R1 make the LED1 just from the bright to dark. 3. What is the status of the LED1 when the light strikes the CDS? And what is the voltage at Vin?  4. What is the status of the LED1 when the CDS is blocked? And what is the voltage at Vin?  5. Use oscilloscope to observe the voltage at Vin, what is the response time when block and unblock the CDS?  15
  16. Thực hành cảm biến Blocks to be demonstrated: Thumbwheel Switch Status Display Single Chip Out Control 2 Out Control 3 EPROM DC Power +5V, GND A/D Converter Select / Chip Potentiometer 16
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