Raw data filled with zeros.

[RodHenke]

I'm currently using a kistler 9272 dynamometer for measuring a force and a torque. Also using 2 kistler amplifiers type 5011 and a NI acquisition board NI USB-6218. I recently started calibrating the parameters for the amplifier but I have found this to be extremely complicated. The transducer sensitivity (T) in the dynamometers datasheet is around 3.85 pC/N but putting weights and estimating the T it goes around 1.65pC/N. Those values shouldn't be so far apart. Sample rate: 1kHz

One thing that I have found is that in the raw data several points come up as a zero value during the acquisition and this may pull the mean value of the force measured down and thus explaining the decrease in the T value. I tried several filters and several configurations but those points are always there. Those values seem strange because they can be all put in a straight line.

Figure 1 - No filter no smoothing

Figure 2 - filter lowpass at 100Hz but no smoothing

The other issue is regarding a strange recovering on the Voltage signal. After taking the weights off the signal decreases fast and after a while it goes up slowly. What could be causing this? (figure 3)

Figure 3 - Filter bandstop at 45-65 and smoothing

[Wart]

How does the signal look if you watch it with an oscilloscope?  I'd like to narrow the problem down to LabVIEW/DAQ related or Kistler related.

Are the piezo sensors designed to handle static loads like you putting weights on them?  I worry that the capacitance from you loading them might decay over time.  That'd be easy to see with a scope once you put the weights on the sensor.

[Zwired1]

I ran your VI with a couple simulated sines with noise and did not see the zeros or the mean value drift. 

It seems like both symptoms are caused by the DAQ step -- they're not being introduced by the filters or LVM save steps.

What does the signal coming out of the DAQ assistant look like (before filtering, etc)? 

Looks like you're saving every .2 sec -- can the instrument support this rate?

The zero values in your picture looks like they may be periodic -- what is the period?

BTW, setting up an infiinite loop and requiring the user to hit the abort button to stop the VI is not a good idea.