DH Instruments PPC4, Operation And Maintenance Manual

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3. OPERATING PRINCIPLES
Page 55 © 2009 DH Instruments, a Fluke Company
3.2.29.1.3 Scaling Factor (Scale)
Scale specifies the lower limit for scaling for the threshold uncertainty. If a
Q-RPT is AutoRanged below the scaling factor the threshold remains at the value
determined by the scaling factor (see Table 13).
Example 1 - A premium Q-RPT with default coefficients is AutoRanged to 20% of
the Q-RPT span. The threshold will be at 30% of 0.0024% of the Q-RPT span
rather than 20% of 0.0024% of the Q-RPT span because the default scaling
factor is 30% for a premium Q-RPT.
Example 2 – A standard Q-RPT with default coefficients is AutoRanged to 50% of
the Q-RPT span. The threshold will be at 0.003% of the Q-RPT span rather than
50% of 0.003% of the Q-RPT span because the default scaling factor for a
standard Q-RPT is 100%.
3.2.29.2 Head
Head specifies the uncertainty of head height and is specified in the active height
unit (cm or in). The value is converted to pressure uncertainty with standard
gravity and the calculated density of the fluid at measured pressure.
3.2.29.3 Zero Stability
Zero stability is an uncertainty based on the zero stability of the Q-RPT. Two
values may be specified, one for when AutoZero is ON and one when AutoZero is
OFF (see Section 3.2.22). The values are expressed in percent of Q-RPT span.
Zero stability is inapplicable for Gauge Q-RPTs.
Note
The value for zero stability with AutoZero ON is equal to zero by
default. If edited by the user, the value should be based on how
often the AutoZero has been performed and the uncertainty of
the AutoZero reference (see Section 3.2.22).
3.2.29.4 Control Uncertainty
When delivered pressure uncertainty is desired an additional uncertainty can be
added to the measured pressure uncertainty. The control uncertainty
calculations are based on the active control parameters (see Section 3.2.2) so it
is not necessary to enter additional values.
3.2.29.4.1 Dynamic Control
The control uncertainty during dynamic control when the PPC4 is Ready is equal
to the hold limit (see Section 3.2.2). Dynamic control uncertainty assumes that
the measured pressure is equal to the target pressure with an uncertainty equal
to the control hold limit.
3.2.29.4.2 Static Control
The control uncertainty during static control is defined by the stability setting and
the read rate of the PPC4. Typically, the control uncertainty in static mode is
negligible unless the stability limit is set abnormally high.