Vaisala PTB220 - Manual (Page 61)

C HAPTER 7__________________________________________________ ADJUSTMENT AND CALIBRATION
V AISALA _________________________________________________________________________ 55
CHAPTER 7
ADJUSTMENT AND
CALIBRATION
Introduction
The PTB220 series digital barometers can be fine adjusted and
calibrated against pressure standards that have high accuracy and
stability as well as known traceability to international standards. For
Class A barometers, standards with uncertainty of
±70 ppm (±2
standard deviation value) or better should be used. For Class B
barometers, electronic working standards with uncertainty of
±150
ppm are recommended. Vaisala includes in these uncertainties the
drift of the standard over its calibration interval, for example,
electronic working standards must have an initial calibration
uncertainty of
± 100 ppm and maximum allowed drift of ± 50 ppm
over its calibration interval.
The user cannot erase from the memory of barometer the basic
pressure and temperature adjustment coefficients entered at the
factory. However, the user can make linear and multipoint pressure
corrections on the basic adjustment coefficients. The linear and
multipoint fine adjustments can be activated, deactivated and changed
by the user. The following pressure adjustments are possible for the
user:
* offset adjustment
* offset/gain adjustment
* multipoint adjustment at up to eight pressure levels
Note that calibration is considered not to involve any adjustments.
During calibration, the accuracy of the barometer is verified using a
pressure standard and due corrections against the standard are then