SENSORS

2 Classification of Sensor based on Output• Discrete (sometimes called digital, logic,

or bang-bang) - sensors provide a single logical output (a zero or one)

• Proportional (sometimes called analog) - provide an analog output. The output may be a voltage, current, resistance, or even a digital word containing a discrete value.

For discrete sensors, there are two types of outputs

• the NPN or sinking output,

• the PNP or sourcing output

+ 18 to 30 Volts DC.

0 V

Output

24v DC

0v

PNP Type

Output is Positive

Positive switching

+ 18 to 30 Volts DC.

0 V

Output

24v DC

0v

NPN Type

Output switches through to 0v

Negative switching

Proximity SensorsOptical

Inductive

Reed Switch

Inductive Magnetic

Capacitive

Symbols

Connection

Optical Sensors

Type : Through-beam

Electronic Sensors : Capacitive Proximity Sensor

G

1. Oscillator

2. Demodulator

3. Triggering Stage

4. Switching status LED indicator

5. Output Stage with protective Circuit

6. External Voltage

7. Internal Stabilized Voltage

8. Active Switching Zone (Condenser)

9. Switching Output

1 2 3 4 5

9

76

8

Target

Optical Sensors

Type : Through-beam

Transmitter

Receiver

Optical Sensors

Type : Through-beam

Transmitter

Receiver

Optical SensorsType : Retro

reflective

Optical Sensors

Type : Retro reflective

Reflector (prismatic)

Transmitter / Receiver

T

R

Transmitter / Receiver

Reflector (prismatic)

T

R

Optical Sensors

Type : Retro reflective

Transmitter / Receiver

Reflector (prismatic)

T

R

Optical Sensors

Type : Retro reflective

Optical Sensors

Type : Diffuse

Optical Sensors

Type : Diffuse

Target

Transmitter / Receiver

T

R

Transmitter / Receiver

Optical Sensors

Type : Diffuse

T

R

Transmitter / Receiver

Optical Sensors

Type : Diffuse Sensing distance : much less than reflex type, actual distance depends on colour and reflective nature of the surface

Larger targets result in longer sensing distances

Not suitable for dirty environmentsT

R

Inductive Sensor

Electronic Sensors : Inductive Proximity

Sensor

G

1. Oscillator

2. Demodulator

3. Triggering Stage

4. Switching status LED indicator

5. Output Stage with protective Circuit

6. External Voltage

7. Internal Stabilized Voltage

8. Active Switching Zone (Coil)

9. Switching Output

1 2 3 4 5

9

76

8

Connection cable

LED indicator

Resonant circuit coil

Active surface

High Frequency magnetic field (300 to 800 kHz)

Inductive Sensor

Sensor

OscillationAmplitude

Sensor output signal

ON

OFF

Target

Inductive Sensor

OscillationAmplitude

Sensor output signal

ON

OFF

Sensor

Target

Inductive Sensor

OscillationAmplitude

Sensor output signal

ON

OFF

Sensor

Will detect any conductive material

Quoted distances are for mild steel

Sensor performance can be affected by:- Temperature, Target material, and Target dimensions.

Target

Inductive Sensor

Reed Switch

Glass Tube filled with nitrogen

Reed contacts LED

indicator

Reed Switch

24v

Interference from other magnetic fields must be avoided.

If positioned in mid stroke, switching point will vary depending on direction of appoach.

Maximum current must be limited to avoid burning of the reed contacts.

Reed Switch

Inductive Magnetic Sensor

Connection cable

LED Indicator

Resonant circuit coilHigh Frequency magnetic field

Inductive Magnetic Sensor

Inductive Magnetic Sensor

Inductive principle of operation - but only reacts to magnetic fields

Interference from other magnetic fields must be avoided.

Solid state device - higher switching frequency - 1kHz

Inductive Magnetic Sensor

Capacitive Sensor

Electronic Sensors : Capacitive Proximity

Sensor

G

1. Oscillator

2. Demodulator

3. Triggering Stage

4. Switching status LED indicator

5. Output Stage with protective Circuit

6. External Voltage

7. Internal Stabilized Voltage

8. Active Switching Zone (Condenser)

9. Switching Output

1 2 3 4 5

9

76

8

Connection cable

Adjusting screw

LED indicator

Active surfaceActive electrodeEarth electrode

Electrostatic field

Sensor is looking for a change in capacitance in the active field

Capacitive Sensor

Capacitive Sensor

Capacitive Sensor

Detects any material denser than air. (as long as there is enough of it)

Can be adjusted for sensitivity

Can be affected by dusty environments

Capacitive Sensor

As the level rises the fluid affects the sensor field.

Sensor Symbols

+ 18 to 30 Volts DC.

0 V

Output

Inductive

Capacitive

Optical

Magnetic

Ultrasonic

Normally open

Normally closed

OscillationAmplitude

Sensor output signal

ON

OFF

Sensor

Will detect any conductive material

Quoted distances are for mild steel

Sensor performance can be affected by:- Temperature, Target material, and Target dimensions.

Target

Inductive Sensor

Capacitive Sensor

Detects any material denser than air. (as long as there is enough of it)

Can be adjusted for sensitivity

Can be affected by dusty environments

Target

Optical Sensors

Type : Through-beam

Long sensing distance : up to 30 metres with some devices

Will detect all but very transparent materials

Must be accurately aligned

Transmitter

Receiver

Transmitter / Receiver

Optical Sensors

Type : Reflex

Reflector (prismatic)

Sensing distance : 1/2 to 1/3 of through-beam type.

Not suitable for reflective or transparent targets

Target should be larger than the reflector

T

R

Transmitter / Receiver

Optical Sensors

Type : Diffuse

Sensing distance : much less than reflex type, actual distance depends on colour and reflective nature of the surface

Larger targets result in longer sensing distances

Not suitable for dirty environments

T

R

Interference from other magnetic fields must be avoided.

If positioned in mid stroke, switching point will vary depending on direction of appoach.

Maximum current must be limited to avoid burning of the reed contacts.

Reed Switch

Inductive principle of operation - but only reacts to magnetic fields

Interference from other magnetic fields must be avoided.

Solid state device - higher switching frequency - 1kHz

Inductive Magnetic Sensor