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Bài giảng môn thực hành cảm biến
ThӵFKành cҧPELӃQ 1 75ѬӠ1*ĈҤ,+Ӑ&1+$75$1* .+2$&Ѫ.+Ë BӜ0Ð1&ѪĈ,ӊ17Ӱ [\ NguyӉQ9ăQĈӏQK BÀI GIҦ1*0Ð1+Ӑ& THӴ&+ÀNH CҦ0%,ӂ1 /˱XKjQKQ͡LE͡ 1KD7UDQJQăP ThӵFKành cҧPELӃQ 2 1. MөFÿtFK *L~SVLQKYLrQFiFKÿRÿҥFWKXWKұSYà hiӇQWKӏJLá trӏFӫDPӝWVӕORҥLFҧPELӃQ thông dөQJ 2. Yêu cҫX 7KDPJLDÿҫ\ÿӫFiFEXәLKӑFOêWKX\ӃWYà thӵFKành. 3. NӝLGXQJP{QKӑF SӱGөQJEӝWKtQJKLӋP./-ÿӇÿRÿҥFYà lұSWUình hiӇQWKӏ -CҧPELӃQWLӋPFұQ3UR[LPLW\ -CҧPELӃQQKLӋWÿӝ7HPS37-100) -CҧPEiӃQJyFTXD\5RWDWLRQ$QJOH -CҧPELӃQUXQJVibration) -CҧPELӃQhӗQJQJRҥL (Infrared) -CҧPELӃQTXDQJ&'6 ThӵFKành cҧPELӃQ 3 1.1. CҧPELӃQWLӋPFұQ 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 Æ Vo22 = Low Æ Q1 OFF Æ Buzzer OFF Proximity Sensor LED: Indicator Detect Head S S t t r r u u c c t t u u r r e e : : V CC Output GND Oscillator Trigger Switching Amplifier S S y y m m b b o o l l : : ( ( E E q q u u i i p p m m e e n n t t C C i i r r c c u u i i t t ) ) ThӵFKành cҧPELӃQ 4 When a metallic object approach to the detecting head: Vo = LOW Æ Vo22 = High Æ Q1 ON Æ 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. Æ ThӵFKành cҧPELӃQ 5 1.2. CҧPELӃQQKLӋWÿӝ 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: Temperature (PT100) Sensor Stainless-steel protection tube (Platinum wired wound inside) A B B’ B=B’ S S y y m m b b o o l l : : S S t t r r u u c c t t u u r r e e : : A B’ Voltage Out ThӵFKành cҧPELӃQ 6 • VR2 is used to control the constant current source to 2.25mV • U1 is non-inverting amplifier Æ V16= (2550+10T) mV • U2 is differential amplifier • U3 is voltage follower Æ Adjust VR14 to control Vf1 (offset of U2) • So if Vf1 = 2550mV Æ Vo27 = 100T mV Æ 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). Æ ? 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 Æ ? 5. Adjust VR14 until Vo27 is equal to T/10 V (Calibration complete) Æ ? 6. Put both PT-100 and the mercury thermometer inside hot water. 7. What is the value shown on the mercury thermometer? Æ ? 8. What is the output voltage of Vo27? Æ ? 9. Put both PT-100 and the mercury thermometer inside cold water. ThӵFKành cҧPELӃQ 7 10.What is the value shown on the mercury thermometer? Æ ? 11.What is the output voltage of Vo27? Æ ? 12.What’s the difference between AD590 and PT100 temperature sensor? Æ ? ThӵFKành cҧPELӃQ 8 1.3. CҧPELӃQJyFTXD\ 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: Rotation Angle Sensor S S t t r r u u c c t t u u r r e e : : Knob Plastic Housing CW CCW Output (sliding connection) Excitation Voltage Vout S S y y m m b b o o l l : : ThӵFKành cҧPELӃQ 9 • 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? Æ ? 4. How many degrees you have rotate in step 2? Æ ? 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 Æ ? ThӵFKành cҧPELӃQ 10 1.4. CҧPELӃQUXQJ 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: Vibration Switch Contact: to spring Contact to metal Housing S S y y m m b b o o l l : : S S t t r r u u c c t t u u r r e e : :