Switches and Sensors

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Switches and Sensors
?????????? ??? Chapter 8 Sensor

• For integrated control systems

WUHAN UNIVERSITY OF TECHNOLOGY LOGISTICS ENG.
DEPT. ?????? ??????
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Contents
?????????? ??? Chapter 8 Sensor

• Cable capacitance

• Introduction

• Vacuum electric switch

• Magnetic cylinders

• Reed switch principle

• Vacuum electronic switch

• Sensor principle

• QM/45/ range

• QM/33,34,134 range

• M/40,41,42 range

• Inductive proximity sensors

Click the section to advance directly to it
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Introduction
?????????? ??? Chapter 8 Sensor

• Typical electro-pneumatic systems consist of
• magnetic cylinders and solenoid valves for
  dynamic power
• reed switches and sensors for feedback
• electronic logic for control
• Reed switches and solid state magnetic sensors
  are fitted to cylinders to feedback particular
  positions of the piston

• Solid state proximity sensors can be used to
  replace limit switches, for detecting the
  position of mechanisms or other moving parts
• Reed switches and solid state sensors are small,
  fast, easy to fit and adjust. They simplify
  installation on to the machine application

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Magnetic cylinders
?????????? ??? Chapter 8 Sensor

• Magnetic cylinders have a band of magnetic
  material inset around the circumference of the
  piston
• The polarity is in parallel with the axis of the
  cylinder
• The barrel is made of non ferrous material
• By placing reed switches along the outside of the
  cylinder, signals can be given at the extreme and
  intermediate positions of stroke

Click the illustration to start and stop animation
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Reed switch principle
?????????? ??? Chapter 8 Sensor

• A basic reed switch consists of a small glass
  tube containing soft iron contact reeds normally
  sprung open
• When a magnetic field is in range the reeds will
  become magnetic
• The ends will be of opposite polarity and pull
  themselves together

Click the illustration to start and stop animation
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Magnetic sensor principle
?????????? ??? Chapter 8 Sensor

• In the presence of a magnetic field the
  magnetoresistive sensor has a lower resistance.
  This causes current to be drawn from the base of
  the transistor turning it on
• The circuit incorporates l.e.d., reverse polarity
  protection diodes and suppression diode for an
  inductive load

V
load
0V
sensor
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Reed switches and sensor
?????????? ??? Chapter 8 Sensor

• Slim cylindrical housing
• PVC cable in 2 or 5 metre lengths
• Optional very flexible polyurethane cable
• With or without l.e.d. indicator
• Range of four reed switches and one solid state
  sensor

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Reed switches
?????????? ??? Chapter 8 Sensor

• Basic reed switch
• Shown connected to a relay or solenoid coil with
  diode suppression for d.c. application
• 10 to 30V a.c./d.c.
• Maximum switching power 10 W/VA

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Reed switches
?????????? ??? Chapter 8 Sensor

• Reed switch with l.e.d. indicator
• Three wires emulating p.n.p. sensor
• Current sourced on the black wire to the coil
• Resistor protects l.e.d. from over voltage

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Reed switches
?????????? ??? Chapter 8 Sensor

• Reed switch with l.e.d. indicator and two wires
  only
• Current sourced on the black wire to the coil
• Zener diode provides small voltage drop to turn
  on l.e.d.
• 10 to 240V a.c./170V d.c. 10 W/VA maximum
• Shown with VDR for suppression a.c. or d.c.

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Reed switches
?????????? ??? Chapter 8 Sensor

• Reed switch with l.e.d. indicator
• Three wires emulating n.p.n. sensor
• Current sunk on the blue wire from the load to 0V
• Resistor protects l.e.d. from over voltage

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Solid state switches
?????????? ??? Chapter 8 Sensor

• Solid state magnetically operated p.n.p. output
• Used for applications where vibration levels are
  unsuitable for reed switches
• Magnetoresistive sensor element
• Sensor on l.e.d. indicator
• 10 to 30 V d.c. 200mA maximum

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Reed switches and sensors
?????????? ??? Chapter 8 Sensor

• Neat cylindrical housing with fixed or plug-in
  cable
• Straight or 90o plug-in connector cables
• Optional very flexible polyurethane cable or
  high temperature (150oC) silicon cable
• With or without l.e.d. indicator
• Wide range of reed switches and solid state
  sensors

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Reed switches
?????????? ??? Chapter 8 Sensor

• Plain reed switch
• Plain change-over reed switch
• Three wire reed switch with l.e.d., emulating
  p.n.p. sensor and plug-in cable
• Three wire reed switch with l.e.d., emulating
  n.p.n. sensor
• Two wire reed switch with l.e.d.

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Solid state sensors
?????????? ??? Chapter 8 Sensor

• Output p.n.p. fixed cable
• Output p.n.p. plug-in cable
• Output n.p.n. fixed cable
• Output n.p.n. plug-in cable
• Pulse stretcher. Output p.n.p. fixed cable. When
  operated and released output will remain on for a
  further 30 ms approximately. Suitable for part
  stroke position on fast operating cylinders

QM/134
QM/134/P
QM/134/N
1
QM/134/N/P
QM/134/X
black
0V
Load
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Reed switches and sensors
?????????? ??? Chapter 8 Sensor

• Low profile with dove tail slide for cylinders
  with integral track in extruded body
• Screw tightening
• Fixed cable or plug-in connector cables straight
  or 90o
• With or without l.e.d.

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Reed switches and sensors
?????????? ??? Chapter 8 Sensor

• Low profile with dove tail slide for cylinders
  with integral track in extruded body
• Screw tightening
• Fixed cable or plug-in connector cables straight
  or 90o
• With or without l.e.d.

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Reed switches
?????????? ??? Chapter 8 Sensor

• Two wire with l.e.d. 10 to 240V a.c./170V d.c.
• With high temperature cable
• With very flexible polyurethane cable
• Two wire with l.e.d. and plug in cable 10 to 60V
  a.c./74 d.c.
• Change-over contacts without l.e.d.

M/40
TM/40
M/40//PU
M/40/P
M/40/C
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Solid state magnetic switches
?????????? ??? Chapter 8 Sensor

• Output n.p.n. 10 to 30V d.c. 200 mA maximum
• Output p.n.p. 10 to 30V d.c. 200 mA maximum
• Output p.n.p. with very flexible polyurethane
  cable
• Output p.n.p. with plug-in cable

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Inductive proximity sensors
?????????? ??? Chapter 8 Sensor

• Sense the presence of metal near the tip
• Used as a limit switch for mechanical parts
• Depending on type
• Range 0.8 to 2 mm
• Switching frequency 500 to 2000 Hz
• With or without l.e.d.
• 10 to 30 or 6 to 30 V d.c.
• Normally closed or normally open p.n.p. output
• output

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Cable capacitance
?????????? ??? Chapter 8 Sensor

• Long leads above the standard cable length become
  a long thin capacitor (equivalent circuit)
• Closing the switch shorts the capacitor, the
  instant high current overloads and damages the
  switch contacts
• Fit an inductor (470µH) close to the switch. This
  damps the surge but has a low steady state
  resistance

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Vacuum electric switch
?????????? ??? Chapter 8 Sensor

• Switches contacts at a vacuum set point
• Adjustable between zero and 0.8 bar absolute
• Normally open and normally closed versions
• Up to 250V a.c./d.c. 2A max
• Repeatability or - 0.1 bar
• Reset differential 0.2 bar

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Vacuum solid state switch
?????????? ??? Chapter 8 Sensor

• Analogue output 1 to 5 V proportional to vacuum
• Solid state switched output at vacuum set point
• Adjustable reset hysteresis
• Adjustable from zero to 1bar absolute
• Output n.p.n. or p.n.p. vesions

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?????????? ??? Chapter 8 Sensor
End