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saia-pcd.com Automation stations – the basics
How does communication influence the application's
cycle time?
If the PCD is set as server (master station), it has little to no
control over its partner stations. Should these partner sta-
tions send large amounts of data simultaneously, the PCD
MUST receive them. The receiving/processing of these data
packages takes priority over the application's cycle time.
Depending upon the workload, the cycle time may, as a con-
sequence, be increased. Should several partner stations send
large amounts of data at the same time, the PCD's processing
time may be massively increased.
If the PCD is set as client (slave station), the impact is then
minimal.
The figures below are based on a PCD3.M5340 with a pro-
gram cycle time of 100 ms, excluding additional communica-
tion.
Web server: Displaying a page on a Micro-Browser panel or
PC does not have a major impact. Loading a large file such
as a Java applet or an offline trend during the transfer can
increase cycle time by 40–50%. The same applies when large
files are transferred via FTP.
S-Bus or Modbus communication via Ethernet: Each partner
station running under full load increases the cycle time by
approximately 8%.
Serial S-Bus:
Each slave-type communication at 38.4 kbit/s
increases cycle time by 5% (port #2). On PCDx.F2xx modules
the increase is about 17%.
At 115 Kbit/s the cycle time is approximately 20% higher.
Modbus RTU:
A client at 115 kbit/s increases cycle time by
about 11% (port #2). On PCDx.F2xx modules the increase is
up to 45%.
What exactly does MTBF mean?Where can I find the
MTBF values for Saia PCD® controllers?
MTBF is the abbreviation for Mean Time Between Failures.
The time referred to is the period of operation between two
consecutive failures of a unit (module, device or system). The
higher the MTBF value, the more “reliable” the device. On av-
erage, a device with a MTBF of 100 hours will fail more often
than a similar device with a MTBF of 1,000 hours. The MTBF
can be calculated in purely mathematical terms or on the
basis of empirical values. Please bear in mind that the MTBF
value of the overall installation is dependent on the values of
the individual switch cabinet components.
You can find an overview of the MTBF values of the PCD
controllers on our support site.
The rate of returns is more relevant in pratice. We analyze all
the devices that come back from the field. The return rates
of the current PCD controllers during the warranty period
(30 months) are as follows:
PCD2.M5xxx:
0.94%
PCD3.M5xxx:
0.99%
PCD3.M3xxx:
1.14%
What part of the memory is lost if the battery fails and
how does the PDC react?
In theory, the user memory of the PCD, which contains the
content of the media such as registers, counters, meters and
flags, as well as the writable part of the DB and text elements,
is lost in the event of a failure of the power supply with a bat-
tery that is additionally weak or defective. We now have to
differentiate between two different types of PCDs.
Controllers that are equipped with an internal microSD card,
store the user program and associated initial values of the
media in a system partition. In the event of the user memory
without backup being lost, this data is reloaded into the
user memory and the program is processed again with the
parameters that were defined at the time of the download
in PG5.
Controllers that do not have an internal file system need a
backup containing the user program and associated media.
This backup can be created with the help of PG5 when
downloading the application. In order that it is possible to
restore the program and the media content, in the case of
empty memory, as a general rule, the last download of an
application should be backuped to an external file system of
the PCD.
If a backup of the application of a PCD is available and the
content of the user memory is not plausible, the application
will be restored from the point at which the backup was
created.
