DAS - DATA AQCUISTION SYSTEM
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Transcript DAS - DATA AQCUISTION SYSTEM
DAQ - DATA ACQUISITION
VIRTUAL INSTRUMENTATION
Dr. Shahin H. Berisha
Math and Science Division
GateWay Community College
Phoenix, Arizona, USA
Outline
1.What is DAQ ?
2.How do I get my captured SIGNALS
into PC?
Live data capturing?
Signals
DAQ - Block Diagram
Sensor
Signal
Conditioner
Non-Elec. Electrical
Quantity SIGNAL
A/D
Converter
Personal
Computer
Elec. Analog Digital
Signal
SIGNAL
Display
Data
Digital
Display
SENSOR - PROBE
Converts any BIO, CHM. or PHY
quantity into electrical voltage
(SIGNAL)
BIO Sensor - Hart-rate (Sensor) into el.
signal - voltage
CHM Sensor - pH (Sensor) into el.
signal-voltage
PHY Speed - Speed (Sensor) into el.
signal- voltage
TEMPERATURE SENSOR
Active Sensor
Temperature
Fe
Constantan
Voltage
V
V=f(T)
Input - Output RATIO
C/mV
SENSOR
TEMP.
Temp.
VOLTAGE
Voltage
Time
Time
EXAMPLE
K = 2 oC/mV
Vout = 5 mV
Temp. = k Vout
Temp. = 10 oC
SIGNAL CONDITIONER
Output signal of the sensor is usually
very small signal - consequently:
Very difficult to measure - record
Interference is very high - noise
Signal need to be amplified
Conditioning the Signal
Amplification of the signal
linearization throughout the range
filtering unwanted signals
isolation
etc
Low -level signals are amplified to
increase resolution - higher accuracy
Linearization of thermocouple voltage Same correction factor
Filtering unwanted signals (hardware or
software filter)
AMPLIFIER
R
IC
Vin
R
Vout
EXAMPLE
Measured output voltage of amplifier:
Vout =50 mV, Kprobe=2 oC/mV
Kamplif.=10
Vout
T
K probe
K am plif.
DAQ - Block Diagram
Sensor
Signal
Conditioner
Non-Elec. Electrical
Quantity SIGNAL
A/D
Converter
Personal
Computer
Elec. Analog Digital
Signal
SIGNAL
Display
Data
Digital
Display
A/D CONVERTER
What is ANALOG (CONTINUES)
Signal?
What is DIGITAL (DISCONTINUES)
Signal?
Analog Signal - Consider
single or differential input,
range,
resolution,
sampling rate,
accuracy,
noise.
ANALOG SIGNAL - Variation of Temp. vs Time
DIGITAL SIGNAL - Sampled every 2 minutes
30
24
4,24
18
TEMP ( Time )
6,18
2,16
12
6
10,19
8,20
0,6
0
0
2
4
6
8
10
Time
Sampling Frequency: Every 2 min.
Fast changing Signals - this is very slow frequency
PC finds the ORDERED PAIRS at every
2 minutes and stores in FILE:
t 0
T 6
2
16
4
24
6
18
8
20
10
19
(min)
(oC)
PC Plots ordered pairs - graph,
The two signals are not identical,
What to do so the digital analog signal
are closer?
Comparison of Analog and
Digital Signal
30
24
4,24
18
8,20
TEMP ( Time )
6,18
2,16
12
6
0,6
0
0
2
4
6
Time
8
10
Sampling Frequency
Is how often the A/D conversion occurs
How high can I go with sampling
frequency to increase my accuracy
(Nyquist Criteria)
• Computer hardware
• available memory
For Laboratory purposes
• depend on the sampled quantity
• every second or two
File on the PC
DAQ software allows to:
•
•
•
•
select sampling rate,
graph in real time,
perform statistics,
generate reports
No need to transfer data
LIVE DATA COLLECTION
Let’s collect same live data
live data collection of dc signal (battery
voltage)
live data collection of ac signal (speed
sensor)