Difference between primary and tertiary standard s in metrology
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What is a Primary Standard?
A primary standard is a standard based only on one’s knowledge of the only three fundamental units:
MassLengthTime
In pressure work, this reduces to either a manometer (where the height of the fluid column gives you the pressure) or a dead weight tester, where it is only necessary to know the area of the piston and the value of the mass applied.
Generally, the deadweight tester is too cumbersome to use directly as a pressure gage; this has lead to a plethora of devices to use as secondary standards and as process instruments.
At Harwood we maintain our controlled-clearance deadweight gages by sending our weights and pistons out to be recertified on a regular basis. We also recalibrate our secondary standards against out primary on a regular basis.
What is a tertiary Standard?
A tertiary standard is any measuring device that has been calibrated against a primary standard.
In pressure work, the error band on the primary standard is generally so many percent of reading – the error is the summation of the uncertainty in the weight measurement
plus the uncertainty of the piston measurement; secondary devices are usually reported as +/- a percent of full scale. For most production work, that is sufficient. However, if the device being calibrated is, itself, going to be used as a standard to calibrate others, it should have a primary calibration.
A primary standard is a standard based only on one’s knowledge of the only three fundamental units:
MassLengthTime
In pressure work, this reduces to either a manometer (where the height of the fluid column gives you the pressure) or a dead weight tester, where it is only necessary to know the area of the piston and the value of the mass applied.
Generally, the deadweight tester is too cumbersome to use directly as a pressure gage; this has lead to a plethora of devices to use as secondary standards and as process instruments.
At Harwood we maintain our controlled-clearance deadweight gages by sending our weights and pistons out to be recertified on a regular basis. We also recalibrate our secondary standards against out primary on a regular basis.
What is a tertiary Standard?
A tertiary standard is any measuring device that has been calibrated against a primary standard.
In pressure work, the error band on the primary standard is generally so many percent of reading – the error is the summation of the uncertainty in the weight measurement
plus the uncertainty of the piston measurement; secondary devices are usually reported as +/- a percent of full scale. For most production work, that is sufficient. However, if the device being calibrated is, itself, going to be used as a standard to calibrate others, it should have a primary calibration.
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