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Full Scale vs. Grade B Accuracy Gauges

Full Scale vs. Grade B Accuracy Gauges

Full Scale Accuracy
:
When choosing an analog pressure gauge, two of the most important factors to consider are accuracy and pressure range. Most analog pressure gauges express their accuracy as a percentage of the gauge’s full scale. Full scale accuracy means that wherever you are reading within the scale, the error is the same. For example, a 1000 psi pressure gauge with an accuracy of ±1 % of scale (ASME B40.100 Grade Grade 1A) will have an error of ±10 psi whether you measure 100 psi or 1000 psi. For these types of gauges, if your expected measurement is anywhere within the range, the error is consistent.

Grade B (±3-2-3 %) Accuracy:
An alternative option is one with multiple accuracy levels throughout the gauge’s scale. One example of this is a Grade B (± 3-2-3 %) gauge. Grade B accuracy divides the gauge’s accuracy into three sections. The middle half of the range is the most accurate, with a maximum error of ± 2 %, while the first quarter and the last quarter of the range have a maximum error of ± 3 %. Hence, the name 3-2-3 refers to the different accuracy levels from left to the right. For example, a 1000 psi 3-2-3 pressure gauge has an accuracy of ± 30 psi from 0 to 250 psi, ± 20 psi from 251 to 750 psi, and ± from 751 to 1000 psi. Select a Grade B type gauge so that the expected measurement lies in the middle of the gauge’s range to get the best accuracy and longest life out of your pressure gauge.

See the pdf copy of the application note here.