(eBook) - Labview - Distributed Measurement and Control Syst.pdf - Labview - djmajki1

Distributed Measurement and Control Systems

with NI LabVIEW

Introduction

When you need to create a distributed measurement and control system, LabVIEW can

deliver simplified system integration. A distributed system is a set of autonomous

computing components that are linked together by software to make the set of components

act as one integrated system. 1 It is useful for test applications when you need to divide a

project among several computing resources, or when you need to combine information

from different test cells for data analysis. You may need a distributed system to synchronize

a test station with a control system. A distributed system is also useful when you need to

monitor geographically distributed intelligent I/O that can not only measure and control at

the node level, but also log data to a higher level supervisory computer that oversees all the

individual nodes.

Distribution Characteristics

You can describe a distributed system by its distribution characteristic – “loosely coupled”

or “tightly coupled.” Loosely coupled systems typically operate in a publish/subscribe or

client/server model, transferring data from one node to the other. Figure 1 shows a block

diagram of a loosely coupled distributed system – computing nodes running software

networked together. Loosely coupled distributed system examples include:

• PDA receiving data from an embedded device

• Test cells sending data to a central server

• Sensors transmitting data wirelessly to a PC

Figure 1. Ethernet-Based Network of PCs and Other Computing Nodes

1. http://www.infosys.tuwien.ac.at

A tightly coupled distributed system involves hardware components communicating data

or control I/O that are clocked or synchronized together, typically at high speeds. Tightly

coupled system examples include:

• FPGAs communicating with microprocessors

• Set of control nodes on a real-time bus

In addition, you can have hybrid systems, as shown in Figure 2, where you run logic on an

FPGA that works within a real-time computing system, which in turn communicates to a

macro Ethernet-based network.

Windows

Computer

Real-Time Controller

Plug-In Board

Windows VI

Ethernet (Optional)

Real-Time

Programs

I/O

FPGA Logic

Figure 2. Hybrid Ethernet and I/O Network

Network of Computing Nodes

The loosely coupled distributed system topology is used in diverse environments from

research laboratories to manufacturing plants. Whether it is running a particle accelerator

experiment or an efficient canning line, many of the following key elements are present:

• Real-time measurement and control at the node level

• Monitoring, data logging, and system control at supervisory levels

• Ability to integrate standard distributed system protocols such as EPICS and OPC to

tie in existing nodes

• Ability to use standard communications buses such as Ethernet and CAN

• Open programming flexibility to integrate devices such as third-party software,

multiple operating systems, PLCs from many vendors, cameras, and other hardware or

software components

Depending on your application needs, your distributed system may be composed of diverse

components – PCs, high-speed VME/VXI/PXI real-time systems, PLCs, rugged FieldPoint

devices, or any combination of these computing nodes.

Wireless networking technologies such as wireless Ethernet and Bluetooth make it less

tedious to deploy a distributed system. Ultimately, strong software integration is the key to

integrating the system. If you need to scale this system over time, the software must also be

open enough to add new technology without severely disrupting the system or starting over.

ni.com

LabVIEW Tools for Integrating and Managing a Distributed System

With the LabVIEW platform, you can develop this type of distributed system faster, and

maintain long-term adaptability. LabVIEW graphical programming makes it easier to

develop these systems through the following key areas:

• Consistent development paradigm that scales from Windows, to Linux, to Solaris, to

Mac OS X, to RTOSs, to embedded targets

• Interfaces to open networks including TCP/IP, UPD, ActiveX, .NET Web services, and

so on

• Productivity tools to build networked applications, such as

– DataSocket live data streaming transfer client/server protocol based on TCP/IP

– Built-in Web server that requires no programming

– Communications wizard that generates code to communicate from real-time

systems to desktop systems

• Timing and synchronization functionality that take advantage of hardware features to

integrate I/O

Figure 3. TCP/IP Server Application Block Diagram

As LabVIEW extends to new platforms beyond the desktop computer, the environment will

continue to improve the tools you need to build improved integrated distributed systems

rapidly.

The core development system can integrate with thousands of different types of I/O

available from many vendors. It also includes hundreds of analysis and visualization

functions. LabVIEW has specialized tools for monitoring, alarming, operator security, and

data logging to accelerate development of macro distributed applications. In addition,

LabVIEW has tools for dedicated high-performance real-time control. Finally, the software

is an open development environment that can integrate third-party code as well as generate

LabVIEW DLLs and shared libraries for use in other systems.

(eBook) - Labview - Distributed Measurement and Control Syst.pdf

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