Abstract: Provided is a method and apparatus for measuring evaporative vehicle emissions in a fixed-volume enclosure. The method comprises the steps of providing a volume compensation means in fluid communication with a test chamber for compensating for changes in the test chamber fluid volume, where n is a positive integer, measuring the temperature of the test chamber fluid at the sample times t.sub.n, measuring the absolute fluid pressure of fluid at the sample times t.sub.n, determining the density of the evaporative emissions and the test chamber fluid at selected sample times t.sub.n, determining the mass of evaporative emissions present in the chamber, determining the theoretical volume change of the test chamber fluid at said sample times t.sub.

Abstract: Provided is a method and apparatus for measuring evaporative vehicle emissions. In accordance with the invention, there is provided a leak-tolerant apparatus for use in cooperation with an absolute fluid pressure sensor for measuring evaporative emissions for motor vehicles in accordance with prescribed fluid-temperature profiles. The apparatus includes control means in electrical communication with fluid temperature sensor, a fluid pressure sensor and a volume compensation device for determining the quantity of fluid required to be provided to or evacuated from the volume compensation device in accordance with the ideal gas law. In operation, the control means compares the mass flow, volumetric flow, total mass or total volume with the rate or total change in temperature and pressure and corrects a flow metering device so as to allow more or less fluid into or out of the volume compensation device to achieve the desired test chamber volume compensation.

Abstract: Provided is a method and apparatus for measuring evaporative vehicle emissions in a fixed-volume/variable temperature test chamber. The method comprises the steps of providing a volume compensation device in fluid communication with a test chamber for compensating for changes in the test chamber fluid volume, determining the density of the evaporative emissions and the test chamber fluid in mass per unit volume at selected sample times t.sub.n, where n is a positive integer, measuring the temperature of the test chamber fluid at the sample times t.sub.n, measuring the absolute fluid pressure of fluid at the sample times t.sub.n, determining the difference in the test chamber fluid volume between successive sample times t.sub.