Experimental Physics and
Industrial Control System

"Bob Dalesio" <[email protected]> · Tue, 16 Mar 2004 05:26:37 -0700

For a 20 second save rate, it is most likely that the
archiver is using a channel access get (ca_get). The time
stamp in the archiver in this case, will be whatever the
time stamp is in the IOC. This is a function of your
timing system. If you have no timing hardware, it is the
vxWorks close, synchronized with other IOCs using a
network time protocol. It would be rare for the time stamp
to be an exact 20 second interval.
Bob
On Tue, 16 Mar 2004 12:40:37 +0100
 Thomas Birke <[email protected]> wrote:

Wang Yanke wrote:
Hi,
When I tried to archive the vacuum data with
ChannelArchiver, I got some data like:
03/09/2004 15:58:23.254187014   0.000
03/09/2004 15:58:43.254186214   0.000
03/09/2004 15:59:00.000000000   0.000
03/09/2004 15:59:03.254185414   0.000
03/09/2004 15:59:20.000000000   0.000
03/09/2004 15:59:40.000000000   0.000
03/09/2004 16:00:00.000000000   0.000
03/09/2004 16:00:20.000000000   0.000
03/09/2004 16:00:40.000000000   0.000
03/09/2004 16:00:43.254181414   0.000
....
I have retrievaled it with CGIExport or ArchiveExport
many times, but

the results were disappointing.

So, Why can't I get the same proper value(e.g.
1.324e-07) as using

"caget" instead of zero?

Furthermore, why the time interval is not the value i
set in the .cfg

file(20 seconds)?

Is there something wrong with the configuration of the
ArchiveEngine

or the retrieval tools?

How can I get the data I want? 
The reason for that behaviour is, that the
Export-functions of the ChannellArchiver

(every function, that formats floats/doubles into
strings) honours the PREC-field of

the connected PV. It's like

sprintf( "%*f", prec, value )
In some cases, it would be better to use engineering- or
scientific-notation instead of decimal notation - or even
ignore the PREC at all. As an exception, a PREC of 0 is
indeed ignored...
We had the same problems with our vacuum values here at
BESSY and started to store the logarithmic values
instead.
The good thing is: The archive has all the values with
full accuracy, so once you change the formatting of the
output, you'll get your values just like you expect them
to be.

But none of the bundled export tools ignores the
PREC-field if it is set to something other than 0.
The "20 seconds" problem actually isn't a problem.

If a new value arrives via ChannelAccess, it is stored
with the accurate timestamp. The other values are not
even stored in the archive (Kay, correct me if I'm
wrong). It's the output-functions again, that produce
these repeated values.
I know this is not really helpful, but it's an attempt to
explain what happens...

Is ther any guideline on whether and how to handle/honour
the PREC field at all?
Thomas

Bob Dalesio
[email protected]
410 557 0297 Maryland
505 667 5643 Los Alamos (New Number)
505 699 1632 Cell Phone
505 667 6087 Our Secretary (Lisa Marie)

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System