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Thực hành cảm biến

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TRƯỜNG ĐẠI HỌC NHA TRANGKHOA 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


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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)


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1.1. Cảm biến tiệm cận

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

Proximity Sensor

LED: Indicator

Detect Head

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VCC

Output

GND

Oscillator Trigger SwitchingAmplifier

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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.


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1.2. Cảm biến nhiệt độ:

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’

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A

B’

Voltage Out


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• 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


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.


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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? ?


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1.3. Cảm biến góc quay

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.


Rotation Angle Sensor

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Knob

Plastic Housing

CW

CCW

Output(sliding connection)

ExcitationVoltage

Vout

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• 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.



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 ?


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1.4. Cảm biến rung

The vibration switch is normally open with vibration springs. When a vibration

occurred, the switch changes to close state and the switch turns ON.


Vibration Switch

Contact:to spring Contact

to metal

Housing

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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


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?


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1.5. Cảm biến hồng ngoại

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.


Transmitter(Infrared Emitting Diode)

Receiver(Photodiode)

Anode

Cathode

Transmitter Receiver

Vout_U2

Vout_U3

Infrared Sensor


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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



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?


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1.6. Cảm biến quang

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.


Infrared Sensor

LeadWires

CaDmium Sulphide(Orange part)

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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



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?


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BBlloocckkss ttoo bbee ddeemmoonnssttrraatteedd::

Single ChipOut Control 2Out Control 3

Status Display

EPROM

Thumbwheel Switch

DC Power+5V, GND

Select / Chip

Potentiometer

A/D Converter

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