Why cannot use external clock for sampling strain measurement

[hgmittal]

I tried to use external clock (TTL signal) acquired through NI 9401 to control the sampling rate of the strain measurement through NI 9237. But there is always the error numberd 200414 (saying "Possible reason: Requested sample clock source is invalid") even if there is no other channal except the strain. So is NI 9237 not capable of take external sampling clock or it is because of some other reason? How can I realize this function based on what I have (cDAQ 9172, NI 9237, NI 9410 and NI 9215)? If not, what else should I use? Thanks!

[BrowningG]

Hello Hgmittal,

The NI-9237 module uses a sigma-delta analog to digital converter to perform its measurements.  As a result, it requires an oversample clock and a derived sample clock to operate.  Check out this forum post or more information.  This post suggests using an NI 9219 for the strain task since it can accept an external sample clock for a timing source.  If you have an external excitation source, you can use your 9215 to perform a strain measurement with an external sample clock as well.