Data Acquisition (DAQ)

7/28/2019 Data Acquisition (DAQ)

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Data Acquisition (DAQ)


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Signal Classification

YourSignal

AnalogDigital


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Two possible levels: High/On (2 - 5 Volts)

Low/Off (0 - 0.8 Volts)

Two types ofinformation: State

Rate

Digital Signals

Digital

Your Signal


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Digital Signal Information

Digital

Your Signal


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Analog Signals

YourSignal

Analog

Continuous signal Can be at any value

with respect to time

Three types ofinformation: Level

Shape

Frequency (Analysisrequired)


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Analog Signal Information

YourSignal

Analog

Anal

ysis

Required


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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

Noisy, Low-Level

Signal Filtered, Amplified

Signal


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Amplification

Used on low-level signals (i.e. thermocouples) Maximizes use of Analog-to-Digital Converter

(ADC) range and increases accuracy

Increases Signal to Noise Ratio (SNR)

Low-Level

Signal

External

Amplif

ier

DAQ Device

Lead Wires

Instrumentation

Amplifier

Nois

e

A

D

C

+

_


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Data Acquisition Hardware

DAQ Hardware turns your PC

into a

measurement and automation

Compute

r

Your

Signal DAQ

Device

TerminalBlock

Ca

ble


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Terminal Block and Cable

Your

Signal

TerminalBlock

Ca

ble

Terminal Block and Cable route

your signal to specific pins on your

DAQ device

Terminal Block and Cable can be acombination of 68 in or 50 in

50 pin

connector


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DAQ Device

Compute

r

DAQDevice

Most DAQ devices have:

Analog Input

Analog Output

Digital I/O Counters

Specialty devices exist for specific

applications

High speed digital I/O

High speed waveform generation

Dynamic Signal Acquisition (vibration, sonar)

Connect to the bus of your computer

Compatible with a variety of bus protocols

PCI, PXI/CompactPCI, ISA/AT, PCMCIA, USB,


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Configuration Considerations

Analog Input Resolution

Range

Gain Code Width

Mode (Differential, RSE, or NRSE)

Analog Output Internal vs. External Reference Voltage

Bipolar vs. Unipolar


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Resolution

Number of bits the ADC uses to represent a

signal

Resolution determines how many different

voltage changes can be measured

Example: 12-bit resolution

Larger resolution = more precise

representation of your signal

# of levels = 2resolution = 212 = 4,096 levels


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14

100 200150500

Time (ms)

0

1.25

5.00

2.50

3.75

6.25

7.50

8.75

10.00

Amplitude

(volts)

16-Bit Versus 3-Bit Resolution(5kHz Sine Wave)

16-bit resolution

3-bit resolution

000

001

010

011

100

101

110

111

| ||||

Resolution Example 3-bit resolution can represent 8 voltage levels

16-bit resolution can represent 65,536

voltage levels


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Range

Minimum and maximum voltages the ADC can

digitize

DAQ devices often have different available ranges

0 to +10 volts

-10 to +10 volts

Pick a range that your signal fits in

Smaller range = more precise representation ofyour signal

Allows you to use all of your available resolution


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Gain

Gain setting amplifies the signal forbest fit in ADC range

Gain settings are 0.5, 1, 2, 5, 10, 20,

50, or 100 for most devices

You dont choose the gain directly

Choose the input limits of your signal in

LabVIEW

Maximum gain possible is selected Maximum gain possible depends on the

limits of your signal and the chosen

range of your ADC

Proper gain = more precise


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Gain Example

100 200150500

Time (ms)

0

1.25

5.00

2.50

3.75

6.25

7.50

8.75

10.00

Amplitude

(volts)

Different Gains for 16-bit Resolution(5kHz Sine Wave)

Gain = 2

| ||||

Your Signal

Gain = 1

Input limits of the signal = 0 to 5 Volts

Range Setting for the ADC = 0 to 10 Volts

Gain Setting applied by Instrumentation

Amplifier = 2


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Grounding Issues

To get correct measurements you mustproperly ground your system

How the signal is grounded will affect how we

ground the instrumentation amplifier on theDAQ device

Steps to proper grounding of your system:

Determine how your signal is grounded

Choose a grounding mode for your Measurement

SystemMeasurement

System

Signal

Source V

S -

+

V

M


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Signal Source Categories

Grounded

+

_ Vs

Floating

+

_ Vs

SignalSource


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Grounded Signal Source

Signal is referenced

to a system ground

earth ground

building ground

Examples:

Power supplies Signal Generators

Anything that plugs

into an outlet ground

Grounded

+

_ Vs

SignalSource


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Floating Signal Source

Floating Signal is NOT

referenced to a

system ground earth ground

building ground

Examples: Batteries

Thermocouples

Transformers

Isolation Amplifiers

+

_ Vs

SignalSource


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Measurement System

Three modes of

grounding for your

Measurement

System Differential

Referenced Single-

Ended (RSE)

Non-ReferencedSingle-Ended

(NRSE)

Mode you choose

will depend on how

Measurement

System

-

+


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VM

ACH (n)

ACH (n +

8) +

_

Instrumentation

Amplifier

+

_

VS

+

_

AISENSE

AIGND

Measurement System

Differential Mode

Differential Mode Two channels used for each signal

ACH 0 is paired with ACH 8, ACH 1 is paired with ACH 9, etc.

Rejects common-mode voltage and common-mode

noise


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VM

ACH (n)

ACH (n +

8) +

_

Instrumentation

Amplifier

+

_

VS

+

AISENSE

AIGND _

RSE Mode

Referenced Single-Ended (RSE) Measurement made with respect to system ground

One channel used for each signal

Doesnt reject common mode voltage

Measurement System


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VM

ACH (n)

ACH (n +

8) +

_

Instrumentation

Amplifier

+

_

VS

+

_ AISENSE

AIGND

NRSE Mode Non-Referenced Single-Ended (NRSE)

Variation on RSE One channel used for each signal

Measurement made with respect to AISENSE not systemground

AISENSE is floating Doesnt reject common mode voltage

Measurement System


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Choosing Your Measurement

System Signal

Source

Differe

ntial

R

S

E

NR

SE

Measurement

System

Grounded

+

_ Vs

Floating

+

_ Vs

Differe

ntial

R

S

E

NR

SE

Measurement

System


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Options for Grounded Signal

Sources

RS

E

NRS

E

Differenti

al

BETTER+ Rejects Common-Mode

Voltage

- Cuts Channel Count in HalfNOT RECOMMENDED

- Voltage difference (Vg) between

the two grounds makes a ground

loop that could damage the

device GOOD

+ Allows use of entire channel

count

- Doesnt reject Common-Mode

Voltage


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Options for Floating Signal

Sources

RS

E

NRS

E

Differenti

al

BEST

+ Rejects Common-Mode

Voltage

- Cuts Channel Count in Half

- Need bias resistors

BETTER

+ Allows use of entire channel

count

+ Dont need bias resistors


Voltage

GOOD

+ Allows use of entire channelcount

- Need bias resistors


Voltage


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Levels of Software

DAQ

Device

User


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What is NI-DAQ? Driver level software

DLL that makes direct calls to your DAQ device

Supports the following National Instruments

software:

LabVIEW Measurement Studio

Also supports the following 3rd party languages:

Microsoft C/C++

Visual Basic

Borland C++

Borland Delphi


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What is MAX?

MAX stands for Measurement & Automation

Explorer

MAX provides access to all your National

Instruments DAQ, GPIB, IMAQ, IVI, Motion,VISA, and VXI devices

Used for configuring and testing devices

Functionality broken into: Data Neighborhood

Devices and Interfaces

Scales

Icon on

your

Deskto

p


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Data Neighborhood

Provides access to theDAQ Channel Wizard

Shows configured VirtualChannels

Includes utilities fortesting and reconfiguringVirtual Channels


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DAQ Channel Wizard Interface to create

Virtual Channels for: Analog Input

Analog Output

Digital I/O

Each channel has: Name and Description Transducer type

Range (determinesGain)

Mode (Differential, RSE,NRSE)

Scaling


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Devices and Interfaces Shows currently

installed and detected

National Instrumentshardware

Includes utilities forconfiguring and testingyour DAQ devices

Properties

Test Panels


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Test Panels

Utility fortesting

Analog Input

Analog

Output Digital I/O

Counters

Great tool for

troubleshootin

g


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Scales

Provides accessto DAQ CustomScales Wizard

Shows

configuredscales

Includes utilityfor viewing and

reconfiguringyour customscales


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DAQ Custom Scales Wizard

Interface to createcustom scales that

can be used with

Virtual Channels

Each scale has itsown:

Name and

Description

Choice of Scale

Type (Linear,

Polynomial, or

Table)


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Data Acquisition Palette

Analog Input

AnalogOutput

Calibration and

Configuration

Signal

Conditionin

Digital I/O

Counter

DAQ

ChannelName

Constant


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What Type of Device to Use?


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DAQ Device Properties?

DAQ devices have four standard

elements:

Analog input (AI)

Analog output (AO)

Digital I/O (DIO) Counter/Timers

Low-Cost Multifunction DAQ for USB NI


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Low-Cost Multifunction DAQ for USB NI

USB-6008

Small and portable

12-bit input resolution, at 10 kS/s

Built-in connectors for connectivity

2 analog outputs (range 0 to 5 V)

12 digital I/O lines8 single ended inputs (4 differential

inputs)

Input range 1 to 20V

The NI USB-6008 and NI is ideal for

students.

32 bit counter

5 mA Output current drive

Low Cost Multifunction DAQ for USB


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Low-Cost Multifunction DAQ for USB

NI USB-6009

14-bitinput resolution, at 48kS/s


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NI ELVIS: NI Educational Laboratory Vi r tual

I nstrumentation Sui te A custom-designed benchtop workstation and prototyping board to providethe functionality of a suite of common laboratory instruments

provides the functionality of the following

Arbitrary Waveform Generator (ARB) Bode Analyzer

Digital Bus Reader Digital Bus Writer

Digital Multimeter (DMM)Function Generator (FGEN)

Impedance Analyzer

Oscilloscope (Scope)

Two-Wire Current Voltage Analyzer

Three-Wire Current VoltagAnalyzer

Variable Power Supplies

H S l DAQ D i &


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1) Run the MAX program from the labview

software by selecting Tools Measurementand Automation Explorer.

How to Select DAQ Device &

Accessories


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What is MAX?

H t S l t DAQ D i &


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2)Select Devices and Interfaces from the

configuration column.


Accessories

H t S l t DAQ D i &


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3) Choose the NI-DAQmx Devices and

select the PCI-6024E or other if there.


Accessories

H t S l t DAQ D i &


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4)Using right click on the PCI-6024E and selectproperty. In the new window, where the RTSI

cable tab select None while select CB-68LP or

BNC-2120 in theAccessory tab then click OK


Accessories

H t S l t DAQ D i &


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5) Open the Labview program, in the front

panel select functions, input then select

the DAQ Assistant icon.


Accessories


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H t S l t DAQ D i


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7) We have 16 physical input channels from

ai0 to ai15, select a channel like ai0.

How to Select DAQ Device

(Input & Output Channels)

H t S l t DAQ D i


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8) Select your input voltage setup



H t S l t DAQ D i


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9) Now make the connections and select

test then Run to see the input voltage.





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Example



Data Acquisition (DAQ)

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