Method to eliminate periodic noise from data collected with a chromatography system
A method to filter out pump pulses from data collected with a chromatography system is disclosed. Baseline data is collected as a pump delivers solvent to an analytical instrument, which may be the IP signal of a capillary bridge viscometer. A Fourier transform is applied to the data to generate the power spectrum of the baseline signal. Fundamental and harmonic frequencies are determined and a comb filter is constructed therefrom and applied to sample collected from all of the affected instruments. The comb filter may be correlated to the pump and flow rate and stored in data analysis software or database. Other systems using other pumps may also generate associated comb filters, and the resulting filters and the flow rates at which they were generated may be stored in a database accessible to the data analysis software.
1. A method comprising:
collecting data in a chromatography system with an analytical instrument,
wherein the collected data comprises pump pulses caused by at least one pump in the chromatography system,
wherein the at least one pump is computer controlled;
computing a power spectrum of the pulses;
determining a fundamental frequency of the pulses from the power spectrum of the pulses;
constructing a filter to block the fundamental frequency and one or more harmonics of the fundamental frequency;
applying the filter to the collected data, resulting in filtered data without the fundamental frequency and without the one or more harmonics; and
wherein the determining comprises
selecting a region of the power spectrum outside where 1/f noise is not present,
determining a frequency w m corresponding to a maximum power signal in the region,
analyzing power values of frequencies at w m /2 and w m /3 to determine if there is a peak in the power spectrum at the frequencies at w m /2 and w m /3, and
determining the fundamental frequency to be
w m if there is no peak in the power signal at w m /2 or w m /3,
w m /3 if there is a peak in the power signal at w m /3, and
w m /2 if there is a no peak in the power signal at w m /3 and if a peak is present at w m /2.
2. The method of claim 1 wherein the filter is a band-stop filter spanning the drive frequency of the at least one pump.
3. The method of claim 1 wherein the filter is a comb filter comprising a plurality of band-stop filter notches,
wherein one band-stop filter notch among the plurality of band-stop filter notches is configured to block the fundamental frequency and
wherein remaining band-stop filter notches among the plurality of band-stop filter notches are configured to block the one or more harmonics.
4. The method of claim 3 wherein each of the plurality of band-stop filter notches is configured to increase in width with each harmonic of the fundamental frequency.
5. The method of claim 1 further comprising applying a windowing function to the collected data prior to the computing.
6. The method of claim 5 wherein the windowing function is a Hann window.