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34901A frequency measurement limitation?

Question asked by EPICTest on Sep 29, 2011
Latest reply on Sep 30, 2011 by lhornburg

I am using a 34901A/34970A with an automated program to make a frequency measurement of an output from a LED color sensor; I find that it works only about 95% of the time.

When it fails it simply returns '0' although sometimes I have received 9.9E37 which I interpret as an out-of-range indication.

When the measurement succeeds it is in the 12 KHz range so it certainly isn't too fast.  The settings are 10V range, 5 1/2D, FAST.   The signal is a 5V that drops to 0 V for about 12 uS every 106 uS.  I am wondering if because the LO is only about 12% of the cycle length I may be 'on the edge' of the measurement algorithms capability?  There is some over/undershoot but I put a 3.3 nF cap across the probes; it cleared up the over/undershoot but didn't help the measurement.  Please see the attached image from an oscope capture of the signal.