Full Scale vs. Grade B Accuracy Gauges Full Scale Accuracy
When choosing an analog pressure gauge, two of the most importantfactors to consider are accuracy and pressure range. Most analog pressuregaugesexpress their accuracy as a percentage of the gauge’s fullscale. Full scale accuracy means that wherever you are reading withinthe scale, the error is the same. For example, a 1000 psi pressure gaugewith an accuracy of ±1 % of scale (ASME B40.100 Grade Grade 1A) willhave an error of ±10 psi whether you measure 100 psi or 1000 psi. Forthese types of gauges, if your expected measurement is anywherewithin the range, the error is consistent.
Grade B (±3-2-3 %) Accuracy:
An alternative option is one with multiple accuracy levels throughoutthe 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. Themiddle half of the range is the most accurate, with a maximum errorof ± 2 %, while the first quarter and the last quarter of the range havea maximum error of ± 3 %. Hence, the name 3-2-3 refers to the differentaccuracy levels from left to the right. For example, a 1000 psi 3-2-3pressure gauge has an accuracy of ± 30 psi from 0 to 250 psi, ± 20 psifrom 251 to 750 psi, and ± from 751 to 1000 psi.Select a Grade B type gauge so that the expected measurement lies inthe middle of the gauge’s range to get the best accuracy and longestlife out of your pressure gauge.
See the pdf copy of theapplication note here.
