Bài giảng môn thực hành cảm biến

Bài giảng môn thực hành cảm biến

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- CҧPELӃQWLӋPFұQ3UR[LPLW\

- CҧPELӃQQKLӋWÿӝ7HPS37-100)

- CҧPEiӃQJyFTXD\5RWDWLRQ$QJOH

- CҧPELӃQUXQJVibration)

- CҧPELӃQhӗQJQJRҥL (Infrared)

- CҧPELӃQTXDQJ&'6

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

Structure:

VCC

Output

GND

Oscillator Trigger Switching

Amplifier

Symbol: (Equipment Circuit

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

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’

Symbol:

Structure:

A B’

Voltage Out

• 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

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?

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

Structure:

Knob Plastic Housing

CW

CCW

Output

(sliding connection)

Excitation Voltage Vout

Symbol:

• 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?

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 metal

Housing

Symbol:

Structure:

When vibration switch is OFF :

555 Timer (U2) OFFÆ no output at Vo10 Æ Buzzer OFF

When vibration switch is ON :

555 Timer (U2) ON Æ pulse output at Vo10 Æ 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?

1.5 CҧPELӃQhӗQJQJRҥL

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:

Transmitter

(Infrared Emitting Diode)

Receiver (Photodiode)

Anode

Cathode

Transmitter Receiver

Vout_U2

Vout_U3

Infrared Sensor

U2: Inverting amplifier, Gain = ~1000

U3: differential amplifier, Gain = ~ 22

U4: Comparator, If V+ > V-Æ output = 12V || If V->V+ Æ output = -12V

Use VR2 to adjusted the output frequency f of the 555 Timer Æ Q1 switches ON and OFF Æ Infrared TX emits ON and OFF Æ If no object blocks between TX and RX Æ Infrared RX receives ON and OFF Æ weak pulse signal input to U2 Æ strong pulse signal Æ Vpp = 12V, frequency = f) output at Vout_U2 Æ At resonant frequency Æ VLc obtain maximum Vpp Æ signal amplify again though U3 Æ CR1, C5, R13 converts the AC signal into DC signal at U4 pin3 Æ If U4 pin3 > U4 pin2 Æ 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 Æ

4 Record the voltage at U4 pin2 and U4 pin3 Æ

5 Block an object between the sensor, what is the voltage at U4 pin3? Æ

6 What is the value of Vo17 when nothing block the sensor? Æ

7 What is the value of Vo17 when the sensor is blocked by an object? Æ

8 What is the current frequency of the 555 Timer output? Æ

1.6 CҧPELӃQTXDQJ

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:

Infrared Sensor

Lead

Wires

CaDmium Sulphide (Orange part)

Structure: Symbol:

When light strikes the CDS:

Sensor resistance Æ Vin Æ Q1 (NPN) ON Æ Q2 (PNP) ON Æ Vo23 High

Æ LED1 ON

When no light strikes the CDS:

Sensor resistance Æ Vin Æ Q1 (NPN) OFF Æ Q2 (PNP) OFF Æ Vo23 LOW

Æ 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? Æ

4 What is the status of the LED1 when the CDS is blocked? And what is the voltage at Vin? Æ

5 Use oscilloscope to observe the voltage at Vin, what is the response time when block and unblock the CDS? Æ

Blocks to be demonstrated:

Single Chip

Out Control 2

Out Control 3

Status Display

EPROM

Thumbwheel Switch

DC Power +5V, GND

Select / Chip Potentiometer A/D Converter