Introduction to sensors
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Transcript of Introduction to sensors
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Level I Level I
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Training Series: Level ITraining Series: Level I
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Electrical InterfaceElectrical Interface
The Back-end
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Electrical InterfaceElectrical Interface
Divided into 2 areas:◦Operating voltage
◦Output signal type
Electrical InterfaceElectrical Interface
PowerPower
SignalSignal
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OUTPUT SIGNAL TYPES
Discrete ON or OFF YES or NO
Analog Speed control Position information
MIN MAX
Electrical InterfaceElectrical Interface
SignalSignal
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OPERATING VOLTAGE
Direct Current (DC) Current flows in only
ONE direction Safe, easy-to-handle
power source
Alternating Current (AC) Current changes direction
60 times a second Readily available
Electrical InterfaceElectrical Interface
PowerPower
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A DISCRETE SENSOR IS A SWITCH
Electronics
Sensing SideFront-end
Electronics
Power WiresSwitch
Electrical InterfaceElectrical Interface
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Electronics
BASIC SENSOR CIRCUIT
Sensors with relay output
+
-
Unlike a switch, sensors require power to operate
Electrical InterfaceElectrical Interface
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TYPES OF DISCRETE ELECTRICAL OUTPUTS
Sensors of today use Solid-State outputs, not mechanical relays
Today Yesterday PNP, 3-wire Relay NPN, 3-wire AC/DC, 2-wire
Electrical InterfaceElectrical Interface
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THE NPN & PNP OUTPUT
Functions similar to a switch,But current only flows in one direction
PNPTransistor Mechanical
Switch
Electrical InterfaceElectrical Interface
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THE DIFFERENT TRANSISTORS
What direction do you want current to flow?
NPNAlso called Sinking
Electrical InterfaceElectrical Interface
PNPAlso called Sourcing
+--+
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PNP, 3-WIRE
1
4+
PNP Output3 -
Load
Standard diagram formAs shown in our catalog
The Sensor
The LoadConnector
Pins
Electrical InterfaceElectrical Interface
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PNP, 3-WIRE
1
4+
PNP Output3 -
Load
Watching the current flow
Sensors Power
Output Signal
Electrical InterfaceElectrical Interface
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1
4+
NPN Output3 -
Load
NPN, 3-WIRE
Watching the current flow
Sensors Power
Output Signal
Electrical InterfaceElectrical Interface
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1 ~
3 ~
Load
THE 2-WIRE AC/DC OUTPUT
Functions similar to a switch,But with a small leak
Sensors Power Supply from leakage current
Output Signal
Triac
Electrical InterfaceElectrical Interface
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QUICK REFERENCE:WIRING PNP & NPN
N P NP N P
+
-
Load
First s
ide of load
Second side of lo
ad
Switched sid
e
Positive
Negative
Sensor is PNP
Electrical InterfaceElectrical Interface
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IF GIVEN A CHOICE, WHICH DISCRETE SENSOR TYPE SHOULD I CHOOSE?
PNP or NPN, 3-wire
- Fewer interface problems
- Largest selection- Lowest unit costs
AC/DC, 2-wire- Many interface
issues- Smaller selection- Susceptible to noise
1st CHOICE
2nd CHOICE
1
4+
3 -
Load
1 ~
3 ~
Load
Electrical InterfaceElectrical Interface
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NORMALLY OPEN (NO)VS. NORMALLY CLOSED (NC)
Identifies the non-active state (target not present) of the sensor
Electronics
+
-
Normally Open
Is it off (open)?
Is it on (closed)?
Electrical InterfaceElectrical Interface
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NORMALLY OPEN (NO)VS. NORMALLY CLOSED (NC)
Identifies the non-active state (target not present) of the sensor
Electronics
+
-
Is it off (open)?
Is it on (closed)?
Electronics
+
-
Normally Closed
Electrical InterfaceElectrical Interface
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ANALOG OUTPUTS
Unlike a discrete output with two defined states, analog signals have an infinite number of states.
Discrete
Analog
On
Off
Voltage
Time
Max
Min
Voltage
Time
Electrical InterfaceElectrical Interface
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ANALOG USES
To provide absolute measurement or position information
MeasurementPosition
Electrical InterfaceElectrical Interface
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ANALOG APPLICATIONS!
Spool diameter Rotational position Liquid level Sort parts Determine part
orientation Measure vibration Measure straightness Hydraulic or pneumatic
cylinder position
Expandingpossibilitie
s
Expandingpossibilitie
s
Electrical InterfaceElectrical Interface
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ANALOG DATA
0 10987654321
Measurement
Panel meters Control systems
Electrical InterfaceElectrical Interface
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ANALOG INFORMATION
The many forms for representing measurement or position information
10
0
10
-10
5
-5
20
0
20
4
Voltage
Current
Digital Pulse
Electrical InterfaceElectrical Interface
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ANALOG VOLTAGE
Information contained in varying voltage
Maximum Voltage
0 10987654321
Measurement
Half VoltageNo Voltage
0 10987654321
Measurement
0 10987654321
Measurement
Water Analogy Volt Meter
Electrical InterfaceElectrical Interface
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ANALOG CURRENT
Information contained in varying Current
0 10987654321
Measurement
0 10987654321
Measurement
0 10987654321
Measurement
Maximum CurrentHalf CurrentNo Current
Water Analogy Current Meter
Electrical InterfaceElectrical Interface
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DIGITAL PULSE
Information contained in digital pulse timing
100.00Maximum
measurementHalf wayMinimum
measurement50.000.00Pulse Width
Meter
Start/Stop
Electrical InterfaceElectrical Interface
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ELECTRICAL INTERFACE REVIEW
Operating voltage: Sensor PowerDC: SafestAC: Most available
Output signal typesDiscrete
PNP, 3-wire NPN, 3-wire AC/DC 2-wire
Analog Voltage Current Digital pulse
Electrical InterfaceElectrical Interface
PowerPower
SignalSignal