Lesson 1
Overview of Signals, Transducers, and
Signal Conditioning
TOPICS
A.
B.
C.
D.
The basics of data acquisition (DAQ)
The basics of transducers
The basics of signals
The basics of signal conditioning
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DAQ System Overview
Software
Data Acquisition
Signal
Conditioning
Signal
Transducer
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What is Data Acquisition (DAQ)?
Data Acquisition is defined as the automatic collection of data
from sensors, instruments, and devices in a factory,
laboratory, or in the field.
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Transducer Overview
• What is a Transducer?
• Types of Transducers
Software
Data Acquisition
Signal
Conditioning
Signal
Transducer
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What is a Transducer?
Physical
Phenomena
Signal
Transducer
A transducer converts physical
phenomena into measureable electrical
signals that a DAQ system measures
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Types of Transducers
Phenomena
Transducer
Temperature
Thermocouples
Resistive Temperature Devices
(RTDs)
Thermistors
Light
Vacuum tube
Photo sensors
Sound
Microphone
Force and Pressure
Strain gages
Piezoelectric transducers
Position and Displacement
Potentiometers
Linear voltage differential transformer
Optical encoder
Fluid
Head meters
Rotational flowmeters
pH
pH electrodes
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Signal Overview
Information in a Signal
•
•
•
•
•
State
Rate
Level
Shape
Frequency
Software
Data
Acquisition
Signal
Conditioning
Signal
Transducer
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Signal Classification
Analog
Digital
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Analog Signals
Analog
Continuous signal
• Can be at any value with
respect to time
Three types of information
• Level
• Shape
• Frequency
(Analysis required)
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Analog Signal Information
Analog
Analysis
Required
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Level Examples
Common examples of
level measurements
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Shape Examples
Common examples
of shape measurements
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Frequency Examples
Common
examples
of frequency
measurements
Analysis
Required
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Digital Signals
Digital
Two possible levels:
• High/On (2 – 5 Volts)
• Low/Off (0 – 0.8 Volts)
Two types of information:
• State
• Rate
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Digital Signal Information
Digital
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State Example
Position of the switch
determines the state of the
signal
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Rate Example
• Shaft spins
• Encoder converts rotation into
two digital pulse trains
• Measure the rate of the pulse
train
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5 Ways to Measure the Same Signal
Analysis
Required
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Signal Conditioning Overview
• Purpose of Signal Conditioning
• Types of Signal Conditioning
Software
Data Acquisition
Signal
Conditioning
Signal
Transducer
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Why Use Signal Conditioning?
• Signal Conditioning takes a signal that is difficult for your
DAQ device to measure and makes it easier to measure
• Signal Conditioning is not always required
• Depends on the signal being measured
Signal
Conditioning
Noisy, Low-Level Signal
Filtered, Amplified Signal
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Amplification
• Used on low-level signals such as thermocouples
• Maximizes use of Analog-to-Digital Converter (ADC) range
and increases accuracy
• Increases Signal to Noise Ratio (SNR)
Noise
+
_
Low-Level Signal
Instrumentation
Amplifier
ADC
Lead Wires
External
Amplifier
DAQ Device
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Signal to Noise Ratio
• Large Signal to Noise Ratio (SNR) is best
• Put amplifier as close to signal source as possible to prevent
amplifying the noise
Signal
Voltage
Signal
Conditioning
Amplification
Noise in
Lead
Wires
DAQ Device
Amplification
Digitized
Voltage
SNR
Amplify only at DAQ
Device
.01 V
None
.001 V
x 100
1.1 V
10
Amplify at Signal
Conditioning and
DAQ device
.01 V
x 10
.001 V
x 10
1.01 V
100
Amplify only at
Signal Conditioning
.01 V
x 100
.001 V
None
1.001 V
1000
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