NI-9467 TAI time convertion

[skol45uk]

Hi

I need to convert TAI time that I am reading from a NI-9467, to a UTC (milliseconds, seconds, minutes, hours, day of year and if possible, year).

I have done the seconds bias subtrations from TAI time to get UTC time.

I've extracted the milliseconds, seconds, minutes, and hours value. But to compute the day of year, I am having problems determining what TAI value zero, represents on the Gregorian calendar. It seems to be 1/1/1970. But I am unable to verify this online on wiki or anywhere. Nowhere I have come across confirms the date of TAI 0nanoseconds.

Can anyone confirm what the TAI zero time is from an NI-9467. And how it is derived from GPS time, as GPS time does not normally contain year so I don't get how the NI-9467 is able to present a TAI time in the first place.

Anybody got any pointers for me? Is there an easier way for me to determine day-of-year?

Thanks

[AlejandroZepeda]

Hi.

The TAI epoch is indeed 1/1/1970.

The "NI 9467 Getting Started" example LabVIEW project contains the "NI 9467 Getting Started (Host).vi" which has code showing how to do the conversion from TAI to LabVIEW timestamp, and includes documentation that mentions that the TAI epoch is 1/1/1970.  You can find the example by going to Help > Find Examples..., selecting the 9467 as your hardware in the lower left corner and limiting results to the selected hardware.  Then look under Hardware Input and Output > Module Specific > Synchronization.

It is true that the GPS transmission does not include the year directly.  Time is transmitted as a 10-bit week number from the GPS epoch (6/Jan/1980) and elapsed seconds since the start of the week.  Knowing the number of elapsed seconds between the TAI epoch of 1/Jan/1970 and the GPS epoch of 6/Jan/1980, (including the 9 leap seconds that occurred during the 1970s, plus the 10 that TAI was already ahead of UTC when it was established), it is possible for the 9467 to provide TAI time.

Hope this helps.

Regards,

Alejandro