Sensaphone SCADA 3000 Users manual - Manual (Page 233)

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Chapter 22: Distributed Control using Visual Basic
Chapter 22: DISTRIBUTeD CONTROL
USING VISUAL BASIC SCRIPT
The SCADA 3000 software allows you to run a control program on the Real-time screen which
has the capability of reading and writing to inputs/outputs of all SCADA 3000 units which are
actively used on the Real-time screen. All I/O points used in the distributed control program
must be referenced on the Real-time screen. The control program can be written in Visual
Basic script, Delphi script, or Java script. This chapter will discuss how to write a control pro-
gram using Visual Basic script. The procedure for writing and running a distributed control
program is identical for using the other languages.
A distributed control program is typically used when multiple units are connected via a radio
network and they must share information or be controlled from one another. In this scenario
all of the SCADA units are online all of the time and I/O values are continuously updated on
the Real-time screen. In the case where multiple units are connected via phone lines, the dis-
tributed control program will read and write to I/O on an as-connected basis according to the
connection frequency programmed on the Real-time screen. In this case, output changes that
must be performed on units which are presently unconnected will be queued until a connection
is made.
Visual Basic
® script is a computer programming language developed by Microsoft ® that pro-
vides the capability for writing sophisticated control programs. Integrated within the SCADA
3000 Real-time screen editor is a Distributed Control Program editor. This editor allows you
to write and compile a program written in the Visual Basic language to perform intelligent
input/output control and mathematical functions. Listed within this chapter are explanations on
common, available functions along with examples on how to make use of them. Online Help is
available from the editor which provides complete documentation for Visual Basic script.
The Distributed Control Program can only run when the Real-time screen is live. The pro-
gram can be set to run periodically using a programmable delay or continuously by time-slicing
the computer's processing capability. A sample template is provided to get you started.
ReqUIRemeNTS
The Microsoft Visual Basic Scripting host must be installed on your computer. This program
can be found on the SCADA 3000 CD.
DISTRIBUTeD CONTROL SCRIPT eDITOR
The SCADA 3000 Real-time screen contains a programming utility that allows you to write
Distributed Control programs and then run them on your computer. To access the Distributed
Control program Editor, click on the DC icon from the System Tab of the Real-time screen
and then click on the palette of the Real-time screen. The System tab is shown below:
Figure 1: Real-Time System tab