DH Instruments FPG8601, Руководство по эксплуатации и обслуживанию

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FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
© 2007 DH Instruments, a Fluke Company Page 38
5.2.2 STABILITY TEST
After the zero condition is set, the stability test must be passed prior to logging zero
information for the system. The stability test first waits a fixed 15s in gauge mode or 25s in
absolute mode to allow any transient pressure effects to pass. Then the load cell output, N,
must be stable within the specified
<Load cell stability criterion for zeroing...>
setting on
the
<Mass>
tab of the
[Internal Limits]
(see Section 6.6.4.5) for three consecutive readings.
In addition, lubrication pressure must be stable within the specified
<RPT stability criterion>
on the
<Pressure>
tab of the
[Internal Limits]
(see Section 6.6.4.2).
5.2.3 STORE ZERO DATA
The final step in zeroing the system is to store the current zero information. The load cell
output, ATM, temperature and lubrication pressure at the end of the stability test are
automatically stored and activated. All new tare information displays on the
<Tare Values>
window (see Section 6.3.3). FPG Tools also logs zero information into the "syszero.log" file
(see Section 9.4). The information logged in this file can be used to determine zero drift for
automated tests.
5.3 INTERNAL CALIBRATION
The internal calibration performs a single point span adjustment on the FPG (see Section 2.3). Using this
function in combination with the
[Zero System]
option is what is required to obtain the best
accuracy for the FPG. Press the
[Internal Calibration]
toolbar option to initiate an internal calibration
(see Section 6.4.2).
For best results, use the [Config], [System Setup], <Run internal calibration after each system zero>
option to couple zeroing and internal calibrations (see Section 6.6.2.1).
An internal calibration must be run prior to taking data after changing measurement modes.
The change in lubrication pressure around the load cell can cause a span shift that must be taken
into account.
The internal calibration is performed in the active conditions of the FPG. This could mean that the FPG is
in a zero condition or at a stable controlled pressure. In either case, the stability criterion must be met
before proceeding (see Section 5.2.2). When stable conditions are obtained, FPG Tools determines the
calibration mass value then calculates a new calibration factor and provides options to activate, log or
ignore the calibration. Since the calibration is not automatically activated, this feature can be used as a
calibration check.
5.3.1 DETERMINING CALIBRATION MASS VALUE
The measured internal calibration mass value is obtained by raising and lowering the internal
calibration mass several times and taking an average. This averaged mass value is used for
calibration factor calculations (see Section 11.3.5.4). The steps below detail the automated
FPG Tools process.
Average the current load cell output (calibration tare). The calibration tare makes it
possible to perform the internal calibration at a pressure. As a result, the load cell span
can be checked at a different point in its range provided a stable pressure is available.
Lower the internal calibration mass and again wait for stability.
Average the load cell output subtracting the calibration tare obtained from Step .
The result is the internal calibration mass.