Access to PXI-6682H TCXO 10 MHz oscillator signal

[gregoryng]

Hello, I am trying to access the TCXO oscillator signal of my PXI-6682H card by routing it to clkout.  I am able to connect the "Oscillator" to clkout, but it does not appear to be disciplined to GPS.  

I have a separate Trimble Thunderbolt generating a 10 MHz signal, and when I view them on an oscilloscope, it's clear that the two are not sync'd.  A 1 MHz clock I generate on PFI2, is synchronized to the Trimble Thunderbolt's 10 MHz output. 

This page PXI_CLK10 Disciplining and Synchronization to a Time Reference Across Multiple PXIe Chassis describes the ability to route the TCXO oscillator signal out of CLKOUT for a 6683H, and implies that this oscillator signal is disciplined by my selected Time Reference.  Does this also apply for a PXI-6682H? 

Demonstration VI attached.  When I ran this code on a PXI-6683H, it did produce a GPS-disciplined oscillator signal.  Is the behavior for the PXI-6682H expected?

Thanks,

Greg

[SamuRei]

Hey Greg,

If this is an issue that you are still running into, I would be curious to know what the status of the "GPS Status" is. Additionally, you could look at the Number of Satellites property to ensure that there is a GPS signal for the Oscillator to be disciplined to. 

I think it would also be useful to run the example that installs with NI Sync: "Discipline PXI_CLK10 to Time Reference". From there we can select the GPS case and go through a lot of the steps that you have in your VI with a couple changed signal routes. Why your code would work with the 6683H and not the 6682H is a bit puzzling to me; I don't see anything obvious that would necessitate configuration differences between the two.

Best,

[gregoryng]

Hi Sam, 

Thanks for weighing in. 

After I looked in the disciplining document I linked, I found this quote which I am not 100% sure how to parse and interpret, but seems potentially relevant. 

The PXI-6682H does not have the ability to do single-board disciplining, and cannot be used in this way.

What is "single-board" disciplining?  

I am away from my equipment, but to respond to your other ideas, I am pretty sure I am getting good satellite signal since I have another test VI that confirms that the PXI-6682H and PXI-6683H are receiving 4+ satellites.  Both my Thunderbolt and the PXI cards are receiving signal from the same GPS splitter.

For the example, do you happen to have a filename for that? Where would it install to?  C:\Program Files (x86)\National Instruments\LabVIEW 2015\examples\...?

[SamuRei]

I think you may have hit the nail on the head here. It looks like the PXI-6682H can be used in conjunction with the 6683H to perform Multi-board disciplining:

"The Multi-Device PXI_Clk10 Disciplining software uses two devices. The first device drives the 10MHz backplane clock, and the second monitors and adjusts the clock relative to an external time reference (for example, IEEE 1588, GPS, or IRIG). No external cabling is required between the modules."

Frankly, I have come up dry in searching for a definition of "single-board" discipline, but was able to find some documentation on the multi-device schema that may help you get going in the right direction:

Synchronizing PXI_Clk10 to the GPS Time Reference

Multi-Device PXI_Clk10 Disciplining Software User Guide

Hope this helps!

[JamesB. · Accepted solution]

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@SamuRei wrote:

It looks like the PXI-6682H can be used in conjunction with the 6683H to perform Multi-board disciplining.

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That's not quite right. Clock disciplining requires two things: a time reference and a steerable oscillator.

The 6682H can interpret time reference (GPS) signals, but its TCXO is not steerable. From the manual, page 3-8: "The 10 MHz TCXO signal is freerunning. It is not disciplined to the board's time reference." (You can get pretty close by synchronizing the 6682H to a PPS, but it's not perfect.)

The 6683H also interprets time reference signals, and its TCXO is steerable. You can use the 6683H for single-board clock disciplining if your chassis has a PXI_CLK10_IN connector; see the link in your original post.

If your chassis does not have a PXI_CLK10_IN connector, your options get a little more complicated and depend on the type of chassis you have (PXI or PXIe). You can use a PXI-6683 (no H; part number 782109-01) for single-board disciplining if your chassis is PXI. If you are in a PXIe chassis, you should pair your 6682H or 6683H (pick one) with a PXIe-6674T for multi-board clock disciplining. Note that the 6674T has an OCXO which is much more stable.