data acquisition reference architecture

Data Acquisition

Reference Architecture

Kitt Farrar

Cell: (513) 894-2321

[email protected]

Developer Education Day 2011

3

Why is Software Important?

Total Measurement Application Cost =

Price of HW + Price of SW + Cost of Development

Visible Price Hidden Costs

Source: National Instruments Survey of Data Acquisition Customers and Prospects 2005

36%,

Price of

HW & SW64%,

Development

Time Costs

4

Oil Well Fracture Pump Monitoring and Analysis Using NI LabVIEW

Application: A system that monitors the operating parameters of a reciprocating pump used in well servicing applications.

Challenge: Building an advanced monitoring system that can survive being mounted directly to an oil well servicing pump in a rugged environment while performing advanced analysis on sensor data.

Products: NI CompactRIO, LabVIEW, LabVIEW Real-Time and LabVIEW FPGA modules, and NI Single-Board RIO

Key Benefit: The high-speed I/O and analysis catch the momentary pressure spikes and vibration indications of the pumps.

“LabVIEW has made the software development side much quicker than our past experiences in C-based

programming. What most C programmers take two years to do, we can accomplish in a couple of months.

We can use that time savings to get to market quicker and capitalize on our competitors‟ lag time.”

– Robert Stewart, Supreme Electrical Services Inc.

5

Agenda• Framework Definition

• Framework Outline

• Demo - Overview

• Framework Modules

• Demo – Adding Your Own Display Windows

• Additional Systems Engineering Components

• Networking Your Data Display

• Substitute Other Options for Logging To Disk

• References

6

Data Acquisition Reference Design

• Open framework: use as-is or custom tailor

• Core functionality:

Configuring Data Acquisition

Acquiring Data

Logging Data to Disk

Displaying Data

• Leverages several SE software components

7

1. Handle all GUI events from the main user interface.

2. Process messages from user interaction or other external processes. Additional

display windows or „plug-ins‟ can be launched from this process.

3. Acquire data continuously. Data is sent via a queue to the data logging process and is

also published via a notifier for any display windows.

4. Log data.

Four Processes

8

Inter-Loop Communication

• Two types of data passed between processes:

Commands

Data

• Commands are sent using the Asynchronous

Message Communication (AMC) library

• Time Domain Data is sent using two methods:

Queues (lossless)

Notifiers (potentially lossy)

10

Demonstration

11

Source Code Organization

• Multiple Project Library

(.lvlib) files

Protects VI namespaces

Defines VI scope (i.e.

public or private)

Organizes the VIs

12

Configuration Module

• Provides the user a way to configure the system

via…

Front Panel Interaction

Loading saved configurations from file

Manipulating configurations currently in memory

13

Data Acquisition Module

• Queue-driven State Machine with 4 states

Idle

Start

Acquire

Stop

• Acquires data from the configured source:

Hardware

Simulated Hardware

File

15

Data Logging Module

• Also a queue-driven state machine

• Saves time domain data to disk using a lossless

queue buffering mechanism

16

Display Windows Module

• Launches windows as reentrant VIs using VI

server from the Main Message Processor

• Display windows are all Queued State Machines

• Add your own display windows using the Display

Template.vit

18

Demonstration:

Adding Your Own Display Windows

19

Additional SE Software Components

• Asynchronous Message Communication

Sending commands between processes

• Channel Monitor XControl

Intuitive front panel channel monitoring utility

• FlexSignal Reference Library

Acquiring from real H/W, simulated H/W, or a file

• GXML Reference Library

Stores system configuration information in XML format

20

Asynchronous Message Communication

• Library for sending messages

Within a Process

Between Processes

21

Creating the Message Queue and

Inserting Messages

22

Processing Messages

23

Networking Your Data Display

• One to Many

LabVIEW Remote Front Panels or

LabVIEW Web Services

• One to One

Network Streams

STM (Simple TCP Messaging)

24

Network Streams (LabVIEW 2010)

• New API for high-throughput streaming over the

network

Open/Read/Write/Close API

Multi-element read/write supported

• Supported on LabVIEW Real-Time and Windows

• Performance is comparable to TCP

25

Seamlessly Stream Data Over the Network

26

Pitfalls of Streaming with Variables

Machine 1 Machine 2

Server

Client Writers

Client Readers

1 2 3 4 1 2 3 4

5 6 7

5 6 745 6 7

• Lack of flow control can result in data loss

• Data may be lost if the TCP/IP connection is dropped

• Data loss does not result in an error, only a warning

1 2 3 4

27

Network Streams in Action

Machine 1 Machine 2

Writer Endpoint Reader Endpoint

123 3 1245 12345

Acknowledge (3)

123 45 45 45 45

Acknowledge (2)

12 345

Flow Control (2)

6789 6789

28

Options for Logging to Disk

1. ASCII

2. Binary

3. TDMS

29

ASCII: Characteristics

• Human readable text file

• Data represented as string

• Common for low speed DAQ

30

ASCII: Write to File

Convert to String

31

Binary: Characteristics

• Not human readable

• Common for high speed DAQ

• Common for multiple channel DAQ

32

Binary: Write to File

33

TDMS: Characteristics

• NI’s recommended file format

• Binary header

• Binary data storage

• Optimized for high-speed streaming

• Versatile data buffers

• Recommended for all DAQ

34

TDMS: Write to File with Primitives

35

TDMS: Create & Set Properties

36

TDMS: Write Data & Close

37

Benchmarks: Performance Comparison

20 Chunks of 10,000 Bytes Each

38

Benchmarks: Size Comparison

20 Chunks of 10,000 Bytes Each

39

Examples

1. Writing data to an ASCII file with timestamps

2. Writing waveform data to file with timestamps

3. Using the Microsoft Report Generation Toolkit

40

For Further Reference

• Data Acquisition Reference Design for LabVIEW

http://zone.ni.com/devzone/cda/tut/p/id/11805

• Data Acquisition Reference Application (The Code)

http://zone.ni.com/devzone/cda/epd/p/id/6438

Refer to the Data Acquisition Reference Application link

for hyperlinks to the additional reference software

libraries that you will need.



41

Additional References

• TDM Streaming (TDMS) VIs


• TDMS File Format Internal Structure


• TDMS Excel Add-In for Microsoft Excel Download


• Creating a Report in Microsoft Excel Using the LabVIEW

Report Generation Toolkit






42

Review

• Framework Definition

• Framework Outline

• Demo - Overview

• Framework Modules

• Demo – Adding Your Own Display Windows

• Additional Systems Engineering Components

• Networking Your Data Display

• Other Options for Logging To Disk

• References

Data Acquisition

Reference Architecture

Kitt Farrar

Cell: (513) 894-2321

[email protected]

Developer Education Day 2011

Questions?

data acquisition reference architecture

Documents