Lesson 6 - Managing Resources

7/27/2019 Lesson 6 - Managing Resources

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TOPICS

ni.com/training

Lesson 6

Managing Resources

A. Understanding File I/O

B. Understanding High-level

File I/O

C. Understanding Low-level

File I/O

D. DAQ Programming

E. Instrument Control

Programming

F. Using Instrument Drivers


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A. Understanding File I/O

File I/O writes to or reads from a file

A typical file I/O operation involves the following process:

Open/

Create/

Replace File

Read

and/or

Write to File

Close

File

Check for

Errors


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A. Understanding File I/OFile Formats

LabVIEW can use or create the following file formats:

BinaryUnderlying file format of all other file formats

ASCIISpecific type of binary file that is a standard used by

most programs LVMThe LabVIEW measurement data file (.lvm) is a tab-

delimited text file you can open with a spreadsheetapplication or a text-editing application

TDMSType of binary file created for NI productsconsisting of two separate files: a binary file and a binaryindex file


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A. Understanding File I/OFile Formats

In this course, you learn about creating text (ASCII) files

Use text files in the following situations:

You want to access the file from another application

Disk space and file I/O speed are not crucial

You must not perform random access reads or writes

Numeric precision is not important


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B. Understanding High-level File I/O

High-level VIs

Perform all three steps (open,read/write, close) for common file I/Ooperations

Might not be as efficient as thefunctions configured or designed forindividual operations

Low-level VIs

Individual VI for each step If you are writing to a file in a loop, use

low-level file I/O functions


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B. Understanding High-Level File I/O

Write to Spreadsheet File Converts an array of double-precision numbers to a text string and

writes the string to an ASCII file

Read From Spreadsheet File Reads a specified number of lines or rows

from a numeric text file and outputs a2D array of double-precision numbers

Write to/Read from Measurement File Express VIs that write data to or read data

from an LVM or TDMS file format


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C. Understanding Low-Level File I/O VIs


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Exercise 6-1

Spreadsheet Example VI

Use a high-level file I/O VI to write to a spreadsheet-readable

file.


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Exercise 6-2

Temperature Log VI

Modify a VI to create an ASCII file using disk streaming.


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Exercise 6-2

Temperature Log VI

What would happen if you used the Write to Measurement

File Express VI inside the While loop?


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D. DAQ Programming

1. Signal

2. Terminal Block

3. Cable

4. DAQ Device

5. Computer


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D. DAQ ProgrammingSoftware Overview

NI-DAQmx Driver level software

Detects DAQ devices

Installs NI-DAQmx functions in LabVIEW

Measurement & Automation Explorer Configure and test DAQ device

DAQ Assistant Configurable Express VI used to create a

DAQ application

DAQmx API Provides a set of VIs to program DAQ

applications


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D. DAQ ProgrammingBasic Flow

A basic DAQmx application involves the following process:

Configure

Task

Acquire or

GenerateData

Clear

Task

Create

Task

Start

Task


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D. DAQ ProgrammingCreate Task

Create Virtual Channel VI

Creates a virtual channel and adds it to a task

Use pull-down menu to select the appropriate instance of this

VI


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D. DAQ ProgrammingConfigure Task

Configure timing if reading multiple samples

Sample rate, timing source, etc

Configure triggering if necessary for application

Configures the task to start or stop on a rising or falling digitaledge, analog edge, or analog windows


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D. DAQ ProgrammingStart Task

Starts the task after the task has been configured


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D. DAQ ProgrammingAcquire or Generate Data

Acquire or generate data from the DAQ device

Make sure pull-down menu selection is compatible with task

configuration


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D. DAQ ProgrammingClear Task

DAQmx Clear Task VI

Stops the task

Releases any resources the task reserved

Clears the task


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D. DAQ ProgrammingExample

Example acquisition with triggering


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E. Instrument Control Programming

Virtual Instrument Software Architecture (VISA):

High-level API that calls low-level drivers

Can control VXI, GPIB, serial, or computer-based instruments

and makes the appropriate driver calls depending on the typeof instrument used


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VISA

VISA

Virtual Instrument System Architecture

Serial GPIB VXI USB


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VISAProgramming Terminology

Resource

Any instrument in the system, including serial and parallel ports

Session

When you open a session to a resource, LabVIEW returns a VISAsession number, which is a unique refnum to that instrument

Instrument Descriptor

Specifies the interface type (GPIB,VXI, ASRL), the address of the

device, and the VISA session type (INSTR or Event)


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VISA Alias

Assign a user-defined name to a device or resource in place

of the instrument descriptor


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Open Sessionto

Instrument(s)

Perform I/OOperation(s)

CloseSession to

Instrument(s)

Check forErrors

VISA Programming

VISA functions operate similar to File I/O functions


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VISA Open Function

Establishes communication line to resource

Generally used once per resource

Returns VISA Resource Name


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VISA I/O Functions

VISA Write and VISA Read Functions


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VISA Close Function

Sessions take up system resources

Close sessions before program ends


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VISA Write and Read Example


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VISASerial

The VISA Configure Serial Port VI initializes the port identified

by VISA resource name to the specified settings


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F. Using Instrument Drivers

Organized set of VIs that control a

programmable instrument

Each VI performs multiple instructions

Grouped by operation type(configuration, data, etc)

Reduce development time

Simplify instrument control

Reusable

Common architecture and interface


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Using Instrument Drivers

When you use an instrument driver, the driver contains the

code specific to the instrument

If you change instruments, replace the instrument driver VIs

with the instrument driver VIs for the new instrument, whichgreatly reduces your redevelopment time


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Using Instrument DriversWhere are they?

You can locate most LabVIEW Plug and Play instrument driversin the Instrument Driver Finder

Access within LabVIEW by selecting ToolsInstrumentationFind Instrument Driversor HelpFind

Instrument Drivers Connects you with ni.comto find instrument drivers

When you install an instrument driver

An example program using the driver is added to the NI Example

Finder Instrument driver VIs are added to the Instrument I/OInstrument

Driverspalette in the Functions palette


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Using Instrument DriversExample


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GOAL

Choose One:

Exercise 6-3

Using DAQmx (DAQ)

or

Exercise 6-4

NI Devsim VI(GPIB/serial)

6-3: Explore a DAQmx example program that continuously

acquires data, and modify it to wait on a digital trigger6-4: Install an instrument driver and explore the example

programs that accompany the instrument driver

C O


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DISCUSSION

Choose One:

Exercise 6-3

Using DAQmx (DAQ)

or

Exercise 6-4

NI Devsim VI(GPIB/serial)

In Exercise 6-3, what types of VIs did you use outside of the

While Loop?

In Exercise 6-4, how would modify the example programs if

you wanted to continuously acquire data?


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SummaryQuiz

1. Your continuously running test program logs to a single file theresults of all tests that occur in one hour as they are calculated. If

you are concerned about the execution speed of your program,

should you use low-level or high-level File I/O VIs?

a) Low-level file I/O VIsb) High-level file I/O VIs


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SummaryQuiz Answer

1. Your continuously running test program logs to a single file theresults of all tests that occur in one hour as they are calculated. If

you are concerned about the execution speed of your program,

should you use low-level or high-level File I/O VIs?

a) Low-level file I/O VIsb) High-level file I/O VIs


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SummaryQuiz

2. If you want to view data in a text editor like Notepad, what fileformat should you use to save the data?

a) ASCII

b) TDMS


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SummaryQuiz Answer

2. If you want to view data in a text editor like Notepad, what fileformat should you use to save the data?

a) ASCII

b) TDMS


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SummaryQuiz

3. Which of the following conveys the basic DAQmx programmingflow?

a) Create TaskConfigure TaskAcquire/Generate DataStart Task

b) Acquire/Generate DataStart TaskClear Task

c) Start TaskCreate TaskConfigure TaskAcquire/GenerateDataClear Task

d) Create TaskConfigure TaskStart TaskAcquire/Generate

DataClear Task


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SummaryQuiz Answer

3. Which of the following conveys the basic DAQmx programmingflow?

a) Create TaskConfigure TaskAcquire/Generate DataStart Task

b) Acquire/Generate DataStart TaskClear Task

c) Start TaskCreate TaskConfigure TaskAcquire/GenerateDataClear Task

d) Create TaskConfigure TaskStart TaskAcquire/Generate

DataClear Task


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SummaryQuiz

4. VISA is a high-level API that calls low-level drivers.a) True

b) False


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SummaryQuiz Answer

4. VISA is a high-level API that calls low-level drivers.a) True

b) False

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Lesson 6 - Managing Resources