...
I might try changing the sample-side tubing on one of the transducers, in a long-shot attempt to figure this out, but otherwise I'm stumped.
I got the following replies from Tom and Gordon:
Steve:
Perhaps you have already considered the averaging of the counter board output. It is
counting for approximately 0.1 second, which is applying a low-pass filter equal to
sin
/x where x = 2/pi*f*dt/2 and dt=0.1 sec. This does not nearly correspond to the
attenuation you are seeing at high frequencies. At the Nyquist frequency, 5 Hz, the
attenuation is 0.637 (0.405 for the power spectrum: a rough anti-aliasing filter) and at
1 Hz the attenuation is 0.984 (0.968).
Still not much help. It is perhaps worth noting this in the logbook for future users of
the pressure data.
Tom
We can alter that averaging period. It is the NumPulses parameter in the XML,
currently set to 3000 for pressures and 10,000 for temperatures.
Gordon