Vaisala PTB220 Bedienungsanleitung PDF herunterladen (Seite 62)

USER'S GUIDE_______________________________________________________________________

56 ___________________________________________________________________ M210194EN-A

given in the calibration certificate together with a description of the

international pressure traceability chain.

In calibration laboratory conditions, the pressure readjustment of a

PTB220 series digital barometer is made by first deactivating the

linear and multipoint corrections using both the LC OFF and MPC

OFF commands. All fine adjustments are then cancelled and the

barometer reverts to use the factory set pressure and temperature

adjustment coefficients. By pre-calibrating the barometer over the

relevant pressure range, the user can define the corrections required

for readjustment. The user can select either a simple offset or a two-

point offset/gain readjustment and use the LCI command for this

purpose. The MPCI command is used for the more sophisticated

multipoint correction capability at up to eight pressure levels. When

the new linear and/or multipoint corrections have been entered to the

barometer, the corrections are activated with the LC ON and/or MPC

ON commands. Finally, the barometer can be calibrated to verify its

real accuracy.

In field conditions, a minor offset readjustment is usually all that is

needed. The user must first check what linear corrections the

barometer is currently using before he attempts to readjust the

barometer. As the previous linear corrections will disappear when new

linear corrections are input, the user has to take into account the

previous linear corrections when deciding about the new ones.

Calibration at one point at the prevailing pressure level finally verifies

that the readjustment has been done correctly.

Entering new linear or multipoint corrections will always cancel the

previous corrections. It is advisable to write down the previous linear

and multipoint corrections so that they will not be lost by mistake.

Entering new linear or multipoint corrections or changing their status

will also automatically cancel the valid date of calibration of the

barometer (see Chapter CALD command).

TABLE 7-1 summarizes the adjustment and calibration commands. The

commands are not case sensitive.

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Vaisala PTB220 Bedienungsanleitung Seite 62