Timestamp conversion different in LabVIEW 8

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Timestamp conversion different in LabVIEW 8

Postby Robert Cole » Thu, 29 Jun 2006 02:40:10 GMT

Okay, first a little background as to what we're trying to do... 

We have mobile systems so we have them set up on UTC. Any of a number
of different other systems can connect to these and these other systems
can be in any timezone. For various reasons that I won't go into here,
we ended up building a method to convert these timestamps (the
"automatic" conversion built into LabVIEW was working as we wanted).

So here's the problem: We are converting from LabVIEW 7.1 to LabVIEW 8.0 and the timestamp conversion is DIFFERENT.

Just letting LabVIEW convert timestamps automatically is giving
incorrect times in some areas. I was testing for our customers in
Saskatchewan (Central Time zone with NO daylight savings time change)
and found that LabVIEW was always applying the DST conversion even
after I switched off DST conversion in Windoze *and* rebooted my
computer.

Our little utility for finding timezone (I have attached a super
simplified version here that works west of prime meridian) in LV 7.1
reported my timezone as -7 in standard time and -6 in DST (making it
easy to adjust times).  In LV 8.0+, it always reports my timezone
as -7. The "is DST" output from Seconds to Date/Time.vi  is always
1 if you are in that time of the year (whether you make the conversion
or not).

I am resigned to the fact that I have to change the program (luckily
just one sub-VI for the whole system to change), but how do I read
whether I should do the DST conversion or not?

     Rob


Find Local TimeZone.vi:
 http://www.**--****.com/ 

Re: Timestamp conversion different in LabVIEW 8

Postby rolfk » Thu, 29 Jun 2006 15:10:06 GMT



We have mobile systems so we have them set up on UTC. Any of a number
of different other systems can connect to these and these other systems
can be in any timezone. For various reasons that I won't go into here,
we ended up building a method to convert these timestamps (the
"automatic" conversion built into LabVIEW was working as we wanted).

So here's the problem: We are converting from LabVIEW 7.1 to LabVIEW 8.0 and the timestamp conversion is DIFFERENT.

Just letting LabVIEW convert timestamps automatically is giving
incorrect times in some areas. I was testing for our customers in
Saskatchewan (Central Time zone with NO daylight savings time change)
and found that LabVIEW was always applying the DST conversion even
after I switched off DST conversion in Windoze *and* rebooted my
computer.

Our little utility for finding timezone (I have attached a super
simplified version here that works west of prime meridian) in LV 7.1
reported my timezone as -7 in standard time and -6 in DST (making it
easy to adjust times).  In LV 8.0+, it always reports my timezone
as -7. The "is DST" output from Seconds to Date/Time.vi  is always
1 if you are in that time of the year (whether you make the conversion
or not).

I am resigned to the fact that I have to change the program (luckily
just one sub-VI for the whole system to change), but how do I read
whether I should do the DST conversion or not?

     Rob
I haven't really dealt with timestamp
conversions in LabVIEW 8 yet but in LabVIEW 7 there already was a
specific issue. If you tried to calculate the timezone offset of a
timestamp before LabVIEW 7 you always got current DST status applied.
In LabVIEW 7 this was "improved" that calculating the timezone offset
of an actual timestamp used the timezone offset that was in effect at
the time of the timestamp. However for timestamps before 1970 the old
behaviour of applying the current DST status was used (observed and
checked under Windows only, sorry)

Could that be an issue you are seeing or did LabVIEW 8 revert to the pre 7.0 behaviour (which would be a bug in my opinion)?

Rolf Kalbermatter

Re: Timestamp conversion different in LabVIEW 8

Postby Robert Cole » Thu, 29 Jun 2006 23:40:09 GMT

What I am saying is that LV 8.0+ does not account for DST *at
all*.  If I take a timestamp from another system that is using UCT
(like an RT system using its default)I and look at that timestamp on my
computer, the time shifts by 7 hours. When this timezone is in DST, the
time should shift by 6 hours but it *always* shifts by 7 hours. 

LabVIEW 7 did it correctly.

I have not, yet, found a method of telling if a timestamp should be
adjusted for DST. Not all timezones or portions of timezones use DST. I
would prefer not to rely on calls to Windoze to make this determination
(there are other operating systems out here).

     Rob

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thanks

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3.Waveform Timestamp -> DBL conversion

I'm using the [DBL -> TimeStamp] conversion VI to modify the t0 property of a waveform.  This technique was taken from NI-Scope Express.vi, and sets the relative display position of a plot on a waveform graph.  <br><br>The problem is that this seems to be a one way conversion and it is not possible to recover the DBL value from the converted TimeStamp.  Not only is there no available VI to perform the reverse [TimeStamp -> DBL] conversion, but no property of the TimeStamp shows that the value is changing (I used a probe with not only the value, but everything else available on the property nodes).  I know the TimeStamp changes though, even when it always says zero, because when the DBL going in is changed, the position of the plot on the waveform graph shifts appropriately as the DBL value is changed.<br><br>After much wrangling, I've just realized I can add the t0 DBL as an extra waveform component to recover it later.  This seems cumbersome though, duplicating information, and buggy that any number you convert into a timestamp is used appropriately, but cannot be recovered, and always says 0 when probed.

4.Problems with timestamp conversion

5.Timestamp conversion problem.

I work in the development of a LabVIEW program that communicates with a
server (written in Java). All acquired data is sent via TCP and the
server can read everything (waveforms and other information). However,
there is a problem in timestamp conversion. We don't know how to
convert the milliseconds correctly. The timestamp is inside a waveform,
so we cannot convert it to formatted string.

Example:

Original timestamp: 

13:37:19,639
11/10/2005

String generated with "Flatten to String":

0000 0000 BF71 9ABF  A3D7 0800 0000 0000 

Converted value (Java server):

13:37:19,000
11/10/2005

Does anyone know the algorithm to obtain the milliseconds from this value: "A3D7 0800"? 

Thanks for attention.

My regards,
Vinicius Falseth

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8. LabVIEW tip: easy relative timestamp calculations



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