Download Data Acquisition

ECE 101
Exploring Electrical Engineering
Chapter 7
Data Acquisition
Herbert G. Mayer, PSU
Status 11/30/2015
Derived with permission from PSU Prof. Phillip Wong
Syllabus
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Data Acquisition Device
Analog IO
Analog-to-Digital Conversion
Digital-to-Analog Conversion
Digital IO
Data Acquisition Device (DAQ)

Multifunction IO unit
 Analog input  measures an analog input voltage
 Analog output 
generates an analog output voltage
 Digital input  senses a binary voltage level
 Digital output  generates a binary voltage level
 Timer  reference time base
 Counter  keeps a count of logic events
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Common types of DAQ hardware:
 Internal peripheral card that plugs into an expansion
slot on a host computer
 External module that connects to a host computer by
USB cable, network cable, or wireless.

The DAQ is controlled by software on the host.
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Analog IO
How does a DAQ device measure or generate analog
voltages?
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Measure:
 An analog-to-digital converter samples an input
voltage signal and converts it to digital form.
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Generate:
 A digital-to-analog converter takes digital values and
converts them to an output voltage signal.
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Analog-to-Digital Conversion

Analog-to-Digital Converter (ADC or A/D)
→ A circuit converts an analog signal to a set of
numbers that represents the signal’s amplitude at
regular time intervals.
A/D Conversion
t
t
Analog signal
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Sampling
00000000
01010111
10100100
11011101
:
→
0
→ 87
→ 164
→ 221
Digital values
Definition → Sampling is the process by which the
signal is converted to digital values.
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Digital-to-Analog Conversion

Digital-to-Analog Converter (DAC or D/A)
→ A circuit converts a set of numbers to an analog
signal that represents the digital values at sequential
points in time.
t0:
t1:
t2:
t3:
:
0
3
5
5
→
→
→
→
00000000
00000011
00000101
00000101
Digital values

D/A Conversion
Filter
t
Analog signal
The DAC output typically goes through a
reconstruction filter to “smooth out” the signal.
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Digital IO

Digital IO channels allow the DAQ to interface with
external digital circuits.

A channel can be configured for digital IO:
V
In terms of voltages, a low value is
0 V, and a high value is +5 V (or
+3.3 V for some circuits).
Logic high
Logic low
t
 Input:
Senses a logic low or high level signal
 Output: Generates a low or high signal
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