DH Instruments PPCK PLUS, Operation And Maintenance Manual

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PPCK+™ Operation and Maintenance Manual
Page 47
©2001 DH Instruments, Inc .
3.4 SPECIAL MENU KEY
The [SPECIAL] menu key accesses a menu of functions that are less commonly used or not
normally used in regular operation.
Press the [SPECIAL] menu key to access the SPECIAL menu.
The display is:
Press <1AutoZ> to turn AutoZ ON/OFF and view AutoZ values (see Section 3.4.1).
Press <2Head> to set head height units and change the head fluid (see Section 3.4.2).
Press <3PresU> to customize the choice of pressure units of measure under [UNIT] (see
Section 3.4.3).
Press <4Internal> to access internal settings and functions RPT calibration, remote interface
settings, time and date, resets, user levels and screen saver (see Sections 3.4.4.1 to 3.4.4.8).
3.4.1 AUTOZ
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PURPOSE
To change the offset (zero) of the reference pressure transducer (RPT) relative to a
reference value in order to compensate for RPT zero drift between full recalibrations.
To assure operation within "with autozero" measurement uncertainty specifications
(see Section 1.2.2.1), it is recommended that AutoZ be run (the value of ZOFFSET
updated) at least every 30 days or when PPCK+ has been exposed to temperature
changes exceeding ± 20 ºC (36 ºF).
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PRINCIPLE
How AutoZ Works
The main component of the change over time of the PPCK+ RPTs is zero drift or offset,
independent of span. Rezeroing PPCK+ RPTs relative to a more stable reference
between recalibrations allows lower measurement uncertainty specifications to be
maintained with less frequent full calibrations. The PPCK+ autozero function (AutoZ)
provides full on-board support for the rezeroing process to simplify its application by
the user.
1AutoZ 2Head 3PresU
4Internal