At Colonial Instruments, Inc. we offer full service calibration of pressure instruments. Currently we test and calibrate pressure gauges from 10" Inches of Water Column up to 15,000 PSI. All gauge certificates are traceable to NIST (National Institute of Standards and Technologies). Each instrument is run through a testing process where a minimum of 5 points across the span of the instrument are read and recorded. If a guage is found to be out of calibration, that is, not reading within the manufactures specification in compliance with ASME B40.1, the pressure gauge is recalibrated until all readings are within the spcified accuracy.

Accuracy of a pressure gauges is defined as follows:

The difference (error) between the true value and the indication expressed as percent of the span. It includes the combined effects of method, observer, apparatus and environment.
ASME B40.1 and DIN accuracy grades are frequently used:

Grade 4A (0.1% Full Scale)
Grade 3A (0.25% Full Scale)
Grade 2A (0.5% Full Scale)
Grade 1A (1% Full Scale)
Grade A (1% middle half, 2% first and last quarters)
Grade B (2% middle half, 3% first and last quarters)
Grade C (3% middle half, 4% first and last quarters)
Grade D (5% Full Scale)
Measurement Accuracy (% of Full Scale). In cases where the accuracy differs between middle span and the first and last quarters of the scale, the largest % error is reported.

All instruments tested at Colonial Instruments, Inc. receives a unique serial number traceable to NIST, each instrument also receives its own calibration chart with serial number, customer name and address information, purchase order number, induvidual instrument readings, as left, at a minimum of 5 points across the span, the NIST serial number and model of the test standard (instrument used to perform the calibration test), and the last time that the test standard was calibrated. It is reccomended that pressure instruments used in pressure testing, such as, hydrostatic line testing, be calibrated a minimum of once a year. Threfore, all instruments are reccommended to be recalibrated one year from the date of the original calibration tagged on the instrument and its corresponding paperwork.

Click here for a pdf version of a sample calibration data sheet.

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