The act of smoking a cigarette is ostensibly very simple but involves a number of separate actions, each of which can vary from smoker to smoker, there are two stages; Puff and Inhalation:
The smoker can make many changes to these actions and alter the way the cigarette is smoked - all of which may affect the yield he or she derives from the cigarette. Clearly, when smoking a cigarette there is scope for further changes as puff number and interval can be varied. In addition, smokers can change the number of cigarettes smoked in per day.
We have developed a Smoking Analyser (SA7)  to measure the puffing behaviour of consumers when they smoke a cigarette. It measures:-
In addition, the SA7 estimates the amount of tar taken into the mouth, using a method that estimates ‘Optical Tar’ (OT).
The SA7 consists of three main units, a special cigarette holder, a Data Acquisition and Transmission (DAT) unit and a computer.
A number of commercial devices for measureing puffing parameters are now available to purchase, including the Plowshare CReSSsmicro™  and CReSS which are now owned by Borgwaldt KC and the SPA/M from Sodim. However, none of these units are able to estimate the tar taken into the mouth.
Cigarette smoke is drawn/puffed through the cigarette holder. The flow of smoke leaving the cigarette towards the smoker’s mouth is measured by recording the pressure on each side of a stainless steel orifice inside the holder. Higher flows through the holder result in greater pressure differences.
The SA7 DAT unit measures these pressure differences at 25Hz and converts them to flow values according to a prior calibration process. The DAT sends the pressure and flow data to the PC for display, storage and calculation of puff volumes as appropriate.
At the same time a measurement is made in the holder of the optical density of the smoke aerosol passing through the holder is made using an LED (660nm) and a detector on opposite sides of the holder.
When no smoke is present, 100% of the light from the LED reaches the detector. When smoke is present, some light gets scattered and therefore less reaches the detector. The extinction of the light signal is measured at 25Hz by the DAT unit and sent to the PC which converts the extinction values and corresponding flow values into a mass of OT - according to a prior calibration process. OT is the term used for the estimate of nicotine free dry particulate matter (NFDPM) measured by this optical method. Eventually, the OT yields for each puff and for the whole cigarette are calculated and these have been shown to be on average within ±1.5mg of the corresponding laboratory measured NFDPM yields.
The calibration procedure involves using a large motorised syringe with known flows and pressures to ensure accurate flow and pressure measurements. Calibration of the relationship between extinction of the light signal and the OT concentration is determined by smoking test cigarettes under a range of smoking regimes, with simultaneous measurement of OT and NFDPM yields.
The DAT also has the ability to measure voltages from several other sources at the same time as recording information about a smoking session. This allows, for example, physiological measurements to be made at the same time as the puffing behaviour measurements.