Hi Jane,
This seems like an issue with the comms from the PLC to the PC that
talks to it. It seems that there is an issue with the data that comes
to the PC that it cant handle. Then the PC tries to 'update' the
database file, or simply crashes out leaving an 'exclusive' connection
not properly closed or able to be re-established.
I would suggest that there are two possible places to look for a
problem here that you might be able to influence. The first would be
to see if there is a DSN created that contains the connection info for
the database, and check to see if the settings match those that the
manufacturer requires. The second would be to check if there is a
matching communication error at or around the same time the database
error / connection error occurs.
Quite often with PLC's (the panel on the wall), when data is being
pushed from the PLC to a PC over a network, or even sometime via a
direct serial connection, the internal buffering on the PLC can
overflow if there is significant enough traffic. The reason for this
is that the amount of data that the associated field panels (door
controllers etc...) collect is usually fed to a primary PLC that has
only a limited throughput. More data coming in than can go out from
the PLC can cause buffer overflow problems and all sorts of strange
errors depending on how the firmware was written. Likewise the comms
from the PLC to the PC tend to have a proprietary structure to the
data payload, which can be sensitive to information corruption across
networks if the network comms arent handled properly. If using a
serial comms scenario then perhaps the cable itself is susceptable to
interference.
So, in short, check the PC for a DSN and that all the settings are in
accordance with the manufacturers specs, and also check for
communications errors (particularly network ones) around the same time
as the error is created with the DB. Does it happen at particualr
times of the day? Is it always on particular days of the week. Does it
happen only when there is a lot of door traffic? Only when there is a
lot of network traffic? When a piece of heavy equipment starts up or
stops? Is the earthing of the system functioning properly? I cant
remember the number of times a problem has come down to faulty
earthing of the the PLC('s). Just a few things for you to look at. I
would suspect however that it is not the DB itself.
Cheers
The Frog
