Digital filter adaptation for tubing response correction at reduced sampling frequencies

The use of a connecting tube to link a pressure tap to a pressure sensor in experiments can have an adverse effect on the accuracy of the measurements. Digital filtering of the measured signals using experimentally determined compensation filters can significantly increase the accuracy of the measurements while avoiding the need for post-processing of data in the frequency domain. This paper examines the nature of the required filters, and presents a method of adapting those filters to suit reduced sampling rates. It is shown that the ideal filter is dominated by non-causal terms, but that the causal terms can be important in some circumstances. A filter, based on experimental data sampled at a high sampling rate, is adapted to suit reduced sampling rates, and the effectiveness of the adapted filters is demonstrated with experimental data. It is shown that the application of the adapted filters substantially reduces the errors introduced by the presence of the connecting tube.