ASTM D4177 Automatic Sampling of Petroleum and Petroleum Products
ASTM D4177 Standard Practice for Automatic Sampling of Petroleum and Petroleum Products
12. Sampler Pacing
12.1 Custody Transfer Meters - Custody transfer meters should be used to pace the sampler where available. When flow is measured by multiple meters, the sampler should be paced by the combined total flow signal. Alternatively, a separate sampler may be installed in each meter run. The sample from each meter run must be considered a part of the total sample and in the same proportion as that meter's volume is to the total volume.
12.2 Special Flow Meters - When custody transfer is by tank measurements, a flow signal must be provided to the sample controller. This signal may be provided by an add-on flow metering device. These devices should have an accuracy of +/-10 % or better, over the total volume of the parcel.
12.3 Time Proportional Sampling - An automatic sampler should preferably operate in proportion to flow. However, sampling in a time proportional mode is acceptable if the flow rate variation is less than +/-10 % of the average rate over the entire parcel.
