DC offset removal problem using HP filter

[jcannon]

Hi everyone,

I have acquired a strain gauge signal that has a dc offset in the signal due to the effect of gravity on the load, which needs to be removed... I could average the baseline and substract this from the signal; but I thought a highpass filter with a cutoff of 0.5Hz (signal sample rate is 2kHz) would also work...However, the filtered signal looks very strange (unfiltered signal on left; filtered signal on right... Any ideas why? Code with filter specs is attached.

Any comments greatly appreciated

Regards,

Jack

[johnsold]

Please post some data to go along with the VI.

Lynn

[jcannon]

Hi Lyn,

Please see attached data file... Data were in .lvm; but i saved as .xlsx as i don't think I can attached .lvm files to the forum?

Raw, uncorrected load cell data in a column B ("Force (Filtered)") ... I would have though't that running a zero phase a 0.5Hz HP filter (by filtering forwards and backwards) would be a much simplier option for removing the effect of gravity of the leg at rest on the strain guage than finding a quiet period in the at rest signal, averaging it, then offsetting that value from the entire signal by substraction.... Perhaps not?

Thanks for taking the time to look at this for me.

Regards,

Jack