GPS with PXI-6608 and RealTime OS

[MF]

Hello,


Here are the facts:

My goal is to decode a GPS Time from a GPS card but here are the facts:

I am running a PXI-1000B chassis using LabVIEW Real Time OS. I have a PXI-6608 Timing Module in Slot 2 and a Symmetricom bc637C PCI GPS card in slot 6. I wire the DC Level IRIG-B signal from the GPS card to the PXI-6608 into pin 15 (PFI7) on a terminal block. I wire the ground to pin 14.

Then I run the "Measure GPS Timestamp.vi" with the LabVIEW target as the PXI chassis. The settings for this VI are

      GPS Counter = Dev1/gpsTimestampCtr0

      GPS Synchronization Method = IRIG-B

      Synchronization Source = PFI7

I do not get valid information and even if I remove the terminal block from the 6608 card, the result (seconds) is not influenced. It appears that the GPS signal is not being seen.

Any suggestions?

Thanks.

Michael Froehlich

[Doug M]

It sounds like you have things connected correctly.  The PCI card you mentioned outputs an IRIG-B signal, which is what the 6608 needs.  However, there are several standards of IRIG-B -- the PXI-6608 will accept TTL standards B000, B001, B002, and B003 only. You may want to double check you GPS receiver to make sure it is outputting its IRIG-B signal as a DC level.  It may be possible for you to select what IRIG-B standard to use as output on your GPS device.
You could check what type of signal you are getting from your GPS receiver with an O-Scope or a multifunction DAQ board. It should be a DC level TTL signal. See the following KB.

You may also want to do simple validation of your PXI-6608 by simply connecting a TTL level switch or signal to PFI7 to make sure that pin is working on your device.

Doug M
Applications Engineer
National Instruments