Measuring Pressure Drop Under Non Ideal Conditions

The method of measurement of the pressure drop (PD) of cigarette filter rods and the draw resistance of cigarettes is defined in ISO 6565-2002 (1). This standard defines the calibration and use of a transfer standard to calibrate the measuring instrument and also defines the measurement procedure for cigarette and filter samples. The procedure described in the standard assumes that the measurement conditions are constant and that the sample is in equilibrium with the measurement environment.

In 2001, the Cooperation Center for Scientific Research Relative to Tobacco (CORESTA) formed a Task Force to investigate the problems associated with the calibration of PD transfer standards that are caused, primarily, by environmental effects. The work of this task force has lead to the harmonisation of the calibration methods between supplier laboratories and to a method for compensation for the effects of atmospheric conditions. These together have considerably reduced the inter-laboratory differences and will eventually lead to a revision of the CORESTA Recommended Method and ISO 6565 Standard.

During the work of this Task Force, it has become evident that further work will be necessary to deal with similar errors encountered during the calibration of PD measurement instruments and during the PD measurement of cigarette and filter rod samples. These errors occur in real measurement situations due to the problems in meeting the ISO 6565 conditions and other necessary requirements. This can give rise to errors in the indicated PD and can considerably degrade the confidence that can be placed in the results.

This paper examines many of the practical problems in the measurement of PD and attempts to estimate the type and magnitude of the errors that might be experienced.