A sampling device for collecting exhaust samples that are proportional in amount to the total amount of exhaust during a given sampling period. A sample flow is pumped through the device, which has a filter for collecting particulates and a sample bag for collecting gas exhaust. The sampling device permits a baseline dilution air flow rate to be fixed by having a pair of parallel valves between the filter and the pump(s). During baselining, one valve is open and adjusted and one is closed and only dilution air flows through the device. Then, for sample acquisition, the second valve is also opened. A processing unit monitors the actual sample flow, compares it to a target flow rate, and adjusts the second valve as needed to maintain the desired proportionality.
Terry L. Ullman; Cynthia Webb