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Calibration of Pressure Balances at The National Laboratory
The National Laboratory for vacuum and vacuum performs calibration of pressure balances. This is the most accurate and complex calibration performed and is done according to current standards and guides.
Purpose
The national laboratories are responsible for maintaining the national reference standards for each measurement quantity and spreading metrological competens and traceability to industry and society at large. The national reference standards are the highest level of traceability in Sweden.
A calibration performed at a national laboratory fullfils all typical traceability and accreditation requirements that commonly exist in industry and society at large.
Method
The pressure balance to be calibrated is connected to the National Labratory's reference pressure balance. The calibration takes place at six to eight pressure points over the balance pressure range. At each level, the balances are balanced against each other, whereby a reference pressure is obtained and used for calculation of results.
There are two methods used in pressure balance calibration. The first method gives a result in form of correction terms at certain pressure levels as well as associated measurement uncertainties. According to this method, the weights of the object does not need to be calibrated before the pressure balance calibration but certiain weight compositions are used to set a nominal pressures. This means that the calibration results only covers the specifik calibrated pressure levels.
The second method involves weighing the weights and piston / cylinder combination at the National Laboratory for mass. The result from that calibration is then used to calculate the effective area of the piston / cylinder combination by means of the reference pressure. This means that the pressure balance is calibrated so that the customer receives sufficient information to be able to measure pressure over the entire pressure balance interval, not just the pressure levels covered in the calibration certificate.
Deliveries
Results are reported in a digital calibration certificate in Swedish or English. The result is presented as correction terms with associated measurement uncertainties or as effective area with measurement uncertainties, depending on the method used for the calibration. The certificate also contains information that the calibration was performed at a National Laboratory.