discrepencies in GPS

[faustina]

I have a PXI-6682 module. When I compare its GPS time in MAX with 3 other GPS receivers that output their time in IRIG-B format, the PXI-6682 is off by 30 seconds.  The other receivers share the GPS antenna, but the PXI-6682 has its own.  Since all are determining time from GPS satillites why is the PXI-6682 so far off?

[Justin_E]

Hi faustina,

You may want to take a look at this KnowledgeBase : http://digital.ni.com/public.nsf/allkb/E123654D4D4E2227862573BF005E5DD7

[faustina]

none of the screen shots in this KB article show up.  do you have another source/link?

[Justin_E]

Hey faustina,

It looks like the images are hosted internally instead of externally... I'm going to work on fixing that. In the meantime, I've attached the two screenshots as FirstSS.jpg and SecondSS.jpg based on where they show up in the KB

[faustina]

both JPG files show the same illustration, is that correct?

also, the properties shown are not what are available on my version of NI-Sync.  I am using NI-Sync 3.1 on LabVIEW RT.  The properties are:

Timing>Time Reference>

 - Time Reference

 - Is Time Reference Present

 - Offset From Time Reference

 - Time Reference Correction (writable)

 - UTC Offset (writable)

 - UTC Offset Valid (writable)

 - Clock Resolution

 - Last Sync ID

I assume I should be setting"Time Reference Correction" if I follow the advice of the KB article.

However, I've tried running the example VI (Set Time Reference.vi) and I get a property error at runtime.  When I look at the PXI-6682 in MAX it also shows errors on Time Reference.  Enclosed is a PPT file that shows all the errors.  MAX says the card is installed and functioning properly, so why are there property issues?

[EEsRULEtheWORLD]

Hi, faustina.

In the Why is My PXI-6682 Timestamp Off When Using GPS Protocol KnowledgeBase, it states that the Clock Adjustment Offset property is in nanoseconds and may only be offset up to 2.3 seconds.  You will need to use LabVIEW to add or subtract the time manually.  For example, in the following screenshot, I added 30 seconds to a time constant with LabVIEW manually:

The reason why the error message states that "the attribute is not supported" is because the clock adjustment offset is greater than 2.3 seconds.  If you input a value less than 2.3 seconds, this error should not be thrown.

Have a great weekend!