Vaisala PTB220 User Manual download pdf (Page 61)

CHAPTER 7__________________________________________________ADJUSTMENT AND CALIBRATION

VAISALA _________________________________________________________________________ 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

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Vaisala PTB220 User Manual Page 61