OIT Basics
Operator Interface Terminals
(OITs) provide much more versatility than traditional mechanical control panels. An OIT
allows a plant floor operator to monitor current conditions of a control system and, if necessary, to initiate a change in the
operation of the system. OITs connect to programmable logic controllers (PLCs) typically through the PLC’s serial
communications port. The OIT can be programmed to monitor and/or change current values stored in the data memory of the
PLC.
OITs can have either text-based or graphics-based displays. A text-based OIT can display printable text characters but no
graphics. Some text-based OITs can display text characters in various sizes. A graphics-based OIT can display printable text
characters of varying fonts and sizes and graphics shapes such as icons, bitmaps, or pictures. Using pictures instead of words
or characters often greatly simplifies the operation of the OIT, making the OIT much more intuitive to use.
Some OITs use touch screen displays while others use a membrane-style keypad. Membrane-style keyboards are best used in
applications in which the keypad is likely to become dirty.
The Maple Systems BLU300 Series OITs are graphics-based membrane-style keypad OITs. Before we get any further into
the operation of these OITs, it is necessary to define some terms that will be used throughout this manual.
Projects
The OIT has two basic segments of internal memory. The
code memory
contains the information required by the OIT that
controls how it operates such as the features supported and how it communicates to a PLC. The OIT programmer does not
have the ability to change code memory. The
project memory
pertains to all of the screens created and any other features that
the OIT programmer can create using the BlueLeaf configuration software. Therefore, the term
project
is used to designate
the file that is sent to the OIT from the BlueLeaf software.
Objects
An
object
is any action that the OIT performs while it is communicating to the PLC. In order to get the operator interface
terminal to ‘do anything’, you must program the OIT with objects. Objects perform actions such as display text or graphics,
write a value to a PLC register, or display a message. Objects most often are graphics shapes that are to be displayed on the
OIT screen. For example, a
Text Object
is used to display text on the OIT. But objects are also used to configure the OIT to
perform some action. For example, a
Jump To Screen Object
tells the OIT to continuously monitor a PLC register that is
used by the PLC to request a new screen. Some objects can display a graphics shape on the OIT screen and perform some
action. For example, a
Function Key Object
creates a graphic object on the OIT that indicates the current state of a PLC
register, when the tagged function key is pressed on the OIT.
Graphics Object
A
graphics object
is any text, icon, or picture that can be displayed on the OIT. Graphics objects are further defined by how
they are composed or created. A
Text Object
is a graphics object that displays text on the OIT screen. A
Bitmap Object
is a
graphics object that displays a bitmap on the OIT screen. Bitmaps are files stored in the OIT to display pictures. Bitmaps
use a pixel-based file format.
Screens
A
screen
is a window of information that can be displayed on the OIT. Screens can appear on the OIT display by a request
from the PLC or by a press from the OIT’s keypad. Each screen can display graphics objects and there is no limit to the
number of graphics objects that can be placed on each screen. The BLU300 Series is capable of storing up to 999 screens ,
but the actual limit is determined by the total amount of memory used for the application (maximum of 256Kbyte). A more
in-depth discussion of screens is covered in later chapters.
1010-0300, Rev 02
Introduction
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