THE CALIBRATION OF A DYNAMIC OLFACTOMETER USING CO TRACER GAS

The paper discusses the most important issue in odor measurement, instrument calibration, which is not carried out by most of the olfactometry laboratories around the world. During the 1980s, the development of olfactometry techniques in the Netherlands and elsewhere in Europe resulted in the introduction of the first draft European Standard for odor measurement by dynamic olfactometer. The critical requirement in the standard is the annual calibration of the dynamic olfactometer against a tracer gas. The calibration is to confirm the dilution ratio as specified by the instrument manufacturer. Unfortunately, most olfactometers in the past did not provide the user with an auto calibration capability and therefore the olfactometry laboratories had to perform the necessary calibrations manually. The calibration of such instruments is both time consuming and labor intensive. The paper discusses the technique of calibrating a dynamic olfactometer using CO gas. A series of CO concentrations are suggested. The effects of the CO sampling point locations (within the system and above the sniffing cup) and the arrangement of the CO sampling tubing (covered and uncovered) are discussed in detail. These sampling arrangements could have significant impacts on the dilution ratio. The Wang Olfactometer was able to achieve averaged instability of 1.7% and accuracy of 9% over the dilution range 1 – 16. It was found that both results were sensitive to the selection of the CO gas range. It is concluded that the calibration of a dynamic olfactometer should be carried out more frequently than once a year.