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saia-pcd.com
Automation stations – the basics
5
4
3
2
1
Cabinet
components
Dedicated
room controller
HMI Visualization
and operating
Automation
stations
Consumption data
acquisition
FAQs for the design of automation systems
What is the difference between local and remote I/Os?
When remote I/Os are accessed, a communications task
always has to run. This task interrupts processing of the
actual ICA task, thus extending the cycle time (page 11).
If cycle time is important and critical, local I/Os are to be
preferred.
Howmany central I/Os per Saia PCD®?
The I/O capacity of a Saia PCD® automation station de-
pends on the maximum number of pluggable I/O mod-
ules, i.e. 64 modules for the Saia PCD2 and Saia PCD3 se-
ries. Each module requires 16 bits. This gives a maximum
of 1024 binary signals overall. Each Saia PCD® CPU in this
system catalogue can read all 1024 binary signals in less
than 10 msec and provide them to the user program
logic. For calculation purposes, one can assume a value
of 0.01 msec per binary I/O and 0.03 msec per analog
value.
In practice, the number of I/Os is limited by the cycle
time required for the user program (see explanation page
11). If the Saia PG5® IL-Editor is used to write a resource-
efficient user program in text form, the 64 I/O slots of the
Saia PCD® automation station will be fully usable. Cycle
time will certainly be well below 100 msec.
If the application software is created using the Saia PG5®
Fupla graphical software engineering tool with ready-
made system templates (Saia PG5® DDC Suite), only half
of the 64 possible I/O modules should be fitted for a cycle
time < 100 msec. Additional communication and data
processing tasks will further increase cycle time.
In the case of fully graphical software engineering for
control-intensive applications combined with additional
tasks (eg BACnet® gateway management functions), it is
advisable not to use more than 300 I/Os per automation
station.
Can third-party local I/Os be connected via S-Bus?
We exclude connecting these in the manual for the Saia PCD®
controllers. SBC S-Bus is a proprietary protocol that is es-
sentially designed for communication with engineering and
debugging tools, for the connection of the management
level or process control systems, and for PCD to PCD com-
munication. It is not suitable for and nor is it approved for the
connection of local I/Os from different manufacturers. I/Os
from third-party manufacturers should be integrated profes-
sionally and safely using one of the many manufacturer-
independent field bus systems.
May the Saia PCD controllers directly connected to
the internet?
When Saia PCD controllers are connected directly to the
internet, they are also a potential target of cyber attacks.
For secure operation, appropriate protective measures must
always be taken. PCD controllers include simple, built-in pro-
tection features. However, secure operation on the internet is
only ensured if external routers are used with a firewall and
encrypted VPN connections.
For more information, please refer to our support site:
How do I connect a third-party device to the PCD if the
protocol is not supported in the PCD firmware and there
is not a corresponding FBox library either?
One of the greatest strengths of the Saia PCD® is that, in ad-
dition to the numerous communication protocols that exist
“off the shelf”, the user has the option of implementing any
protocol he chooses in the user program himself. This is pos-
sible via a serial interface and also via Ethernet.
You can find PG5 example programs on our support site on
this subject.
