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| Instrumentation
Example |
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Typical
Manufacturing Scenario |
| The diagram
shows a typical factory scenario. Over
time various control and monitoring
instruments have been added. Most
of these devices now come complete with
their own control software, are able to
connect to a LAN and can talk to other
devices, usually via some non LAN based
protocol - Typically an RS232 or RS422
serial link. |
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| Even if you're
replacing your older legacy devices with
LAN based systems this invariably still
leaves a gap in interconnection between
instrumentation systems. In most
situations several applications still
have to be run in parallel whilst
switching between them, extracting the
data as you go. Sound familiar? |
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| Ironically, the
more instrumentation is added the more
one tends to move away from the ideal of
central plant monitoring. The data on
the resultant patchwork of connections becomes
ever more transparent to process
operators as system complexity increases |
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Integrated
Data Flow
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Distributed
Intelligence Systems
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| By comparison,
the diagram on the right passes all
important data through a central system
controller. This is done by the
technique of Distributed Intelligence computing that employs
remote data acquisition and control
units (RDU). Each RDU can be programmed
to mimic any I/O function. All
data is now LAN based and can be used in
real time. |
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| The advantages
are clear, instant correlation of
data, access to instrument control from
any point in the network and
standardised modeling though software
carrying only the functions and
facilities needed. |
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| Two basic type
of RDU are available. The only
difference between them is essentially
the data transfer rate required and the
degree of pre-processing of data
required. Type i is the lighter
weight version based on an 8051 CPU core
running at 48Mhz. The second is based
around a low power AMD device running at
500Mhz. |
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| Typical Remote
Data Control Module |
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Advantages of D.
I. Systems |
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REMOTE
DATA UNIT |
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TYPICAL
CONTROLLER |
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| Chelsfield has developed the concept of Distributed
Computing Systems. These have been applied in a wide variety
of situations, principally where some
kind of data acquisition or control
function is required over a large
area. |
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| D.I. Systems are
based around a dedicated central
computer usually termed a controller.
This device communicates over the LAN to
any given set of Remote Data and Control
Units. |
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Fundamentally the hardware
of an RDU is flexible enough to satisfy a
very wide range of I/O functions. This includes driving printers, display
and keyboard devices, communicating with
UARTS and modems. |
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| The function set of
any particular RDU is defined by it's physical
I/O configuration and it's programming
which may be stored in non-volatile RAM
or FPGA's or reside in, EEPROM,
EPROM as part of the firmware. |
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| The picture
(left) shows a typical controller and an
RDU device. Data units are small
and can be wall mounted. The number of
devices attached to the system is
arbitrary and will vary with things such
as cable routes and lead length to
sensors etc. The diagram of an RDU
essentially shows how the device is
connected. Note that two generic
CPU processors are given, either type
may be used depending on the
application, the data throughput, and
degree of pre-processing required. |
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| If the
requirement is for security, simple data
acquisition (analogue or digital) then
the 8051 option may be best. For
on-board DSP and higher volumes of
traffic, including the driving of colour
video displays then the more powerful
processor will be required. |
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| D.I.
SYSTEM FEATURES |
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D.I
systems provide complete
correlation of signals |
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RDU
devices are autonomous and
asynchronous |
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Increase
in computing power
when an RDU is added |
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Can
communicate directly with
each other over a LAN |
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Can
be interrogated from any LAN
terminal |
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Can
satisfy the needs of
safety critical environments |
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Can
monitor or watchdog each
other |
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