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)
