time precision cRIO

[smichau]

Good afternoon

I will use a CRIO with the Real-Time module with Labview. What is the precision ? I need to have a maximum error of 100 ms on a period of 4 hours.

Thanks

Simon Michau

[0utlaw]

Hello Simon,

The precision of the hardware Real-Time clock depends on the model of RIO you're planning to use.  These specifications are available in the Operating Instructions for the respective RIO controllers.

Best Regards,

[smichau]

hello,

Thank you for your answer. I will use the cRIO 9074.

It's written  "Accuracy   200 ppm; 35 ppm at 25 °C". But I don't know what I mean. Is it 200 pulses per minutes, therefore it's a period of 0.3 s...??

Regards

Simon

[smichau]

Oh sorry... It's 200 parts per millions...

But what's the basis of time ?

[0utlaw]

Hello smichau,

This article elaborates on how to calculate absolute possible system clock drift based on the precision of the onboard oscillator:

KnowledgeBase 4SKHG5C1: What Is the Difference Between System Time Drift and Jitter For a Real-Time CompactRIO Controller and How Does it Affect Synchronization?

http://digital.ni.com/public.nsf/allkb/C1DCC95927F9C4CD86257526006FA720

If you have a hard requirement of less than 600 ms of drift per day, you'll likely either need to resynchronize the RIO with a high-precision external timebase via 1588 or similar protocol at intervals or use a RIO with a more precise clock, such as the 9068. 

Best Regards,

[smichau]

Hello.

Thank you verry much. I also asked to a representative of NI. 200 ppm, it's 200us for 1 s, so 3.88 s for 4h !

Therefore I will resynchronize the RIO. I will use the GPS module I think.

Thank you verry much !

Best regards

Simon M.