Getting Absolute timestamps from FPGA 7831R

[Jim001]

I am using a LIN card in my PXI Chassis. This is not an NI product and it cannot access any triggering lines. The device itself returns an array of timestamped measurements but the problem is that the are relative timestamps. I need to have an absolute timestamp so that I can compare timing with other DAQ devices. The only way I can access this is by using a 5V trigger output line. I can set this to trigger on each identifier.

My problem is how to acquire an absolute timestamp. I would not need to get one very often. once every few seconds would be sufficient at worst case.

I have used an M series card analog input which can be triggered and this has given good results.

But I have to use this card for other measurements at the same time so I cannot normally use it as I wish.

The only other option that I have is an FPGA card. RIO 7831R.

Does anyone know how to get absolute timestamps from such a card without having to connect it to any other card?

This would be a great help. 

Thanks in advance

Jimmy

[Seamus_C]

Hi Jim,

Are you using the Digital i/o lines in your application on your m series card.   If not you could use one of the digital lines to read the 5v trigger.  You could then use this trigger in a similar way as you did before using your analogue input.

Seamus

[Jim001]

Hi Seamus

Thanks for responding. The DIO lines on the cards I am using are all static. So no timestamp info can be gathered from them.

Cards I have are:

6733 Analog out

6052E  MIO

6508 DIO

I checked them in MAX and I cannot seem to get timestamps on anything other than Analog input which is in use at the same time.

Regards

Jimmy

[Tom.]

Hello Jimmy,

What environment are you using to acquire your signals? If you are using the LIN card to trigger the other tasks then the information contained within those tasks could be used to try and calculate absolute times from your relative times outputted from your LIN card. For example you could extract the value of 't0' from the waveforms acquired from the NI analogue Input Tasks and then take this time (which is absolute in the form of a timestamp within LabVIEW) and add it to you relative times returned from the LIN card.

To get 't0' from a waveform use the 'Get Waveform Components' VI.

Does this help?

Tom
NIUK

[Jim001]

Hi Tom

I am working in a windows environment. As I may need to Analog input to run all of the time for continuous acquition this is not the best solution. I know I could connect the trigger to one of the analog channels with the output from the LIN card trigger but this is a bit messy.

Absolute timestamp values may be a suggestion for the FPGA development team in the future. It would really help here.

Jimmy

[hannahW]

Hi Jimmy,

You can make product suggestions using links on the following web page:

http://digital.ni.com/public.nsf/websearch/EDA7C01C684ACB6286256FF0000238D5?OpenDocument

I'm not sure there is anything else we can do to help you - the only other alternative would be to use the FPGA board to monitor this trigger line, and when it sees a trigger fires an IRQ to the host program which is waiting on this - and then at this point get the current time in software.

I'm not sure that there is a more accurate way of getting this timing information, as it seems its just a limitation of this LIN card that you have.

Regards
Hannah
NIUK & Ireland