Bubble flow meters,
both the electronic and standard soap bubble meters, are the most
common primary standard air flow rate calibration instruments used
today in industrial hygiene, with accuracies of less than + - 1.0%.
The electronic bubble
meters are relatively expensive, battery operated, must be maintained
and have problems upon repeated use. The standard soap bubble meters
are very fragile, relatively non-portable and awkward to use. Associated
accuracies of both types of devices are <- 1.0%.
Pocket bubble flow
meters are small versions of the standard soap bubble meter. They
are compact, portable, simple to use, inexpensive and an accuracy
of + - 2.0% is reported by the manufacturer.
The primary focus
of this study is to compare the performance of the pocket bubble
flow meters to a primary standard bubble flow meter to determine
whether the pocket bubble flow meters would be an acceptable substitute
without greatly increasing the total error in flow rate measurements.
The pocket bubble
flow meters, of which the three different model sizes from this
manufacturer were included in this study, were connected in series
with an electronic bubble flow meter to an air flow source. Sets
of 100 paired data points were collected over flow rates between
10 and 2000 ml/min. The average flowrates, standard deviations,
percent relative standard deviations and percent accuracies were
calculated.
The meters perfomed
well within the accuracy reported by the manufacturer. Average accuracies
of less than 1.0% were obtained using the meters, except for one
test in which the results were in question. These results are all
within OSHA’s accuracy limit of 5%. The majority of the devices
average flow rates were within one standard deviation of the electronic
bubble flow meters average flow rates. The meters were reliable
with precision values of less than 1.0% for all flow rate tests
conducted, and are within OSHA’s precision limit for flow rate
measurements.
Paired two-tailed
t-tests were performed on the sets of data and a statistical difference
was determined at the 0.05 level of significance. These differences
are very small, would not negatively affect sampling results and
are scientifically insignificant.
It was concluded that
the Pocket Bubble Flow Meters are acceptable substitutes for the
electronic or standard soap bubble meters when used appropriately
and with care
