DH Instruments PPC4, Operation And Maintenance Manual

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3. OPERATING PRINCIPLES
Page 57 © 2009 DH Instruments, a Fluke Company
Note
3
is the denominator of AutoZero uncertainty for the proper
reduction to k=1 for a rectangular distribution assigned to
stability uncertainties.
3.2.29.6 Delivered Pressure Uncertainty
Delivered pressure uncertainty is measured uncertainty defined in Section
3.2.1.2.1 combined with control settings. If in dynamic control mode the
additional uncertainty that is combined is equal to the hold limit. When in static
control mode the uncertainty is the current pressure stability in pressure units per
second multiplied by the update rate of the PPC4.












×






+






× =
2 2 2
12 3
2
2
UpdateRate P
or
HL
U
U
Stab meas
del
where:
U
del
: Delivered pressure uncertainty.
HL : Dynamic mode hold limit.
P
Stab
: Current pressure stability.
UpdateRate : Fixed value in seconds.
Note
The denominator of the dynamic mode uncertainty component
is divided by the
3
because it is considered to be a rectangular
distribution. The denominator for the static control uncertainty
component is divided by the
12
because it also is a rectangular
distribution but represents a full width interval.
3.2.29.7 Using Values Other Than Default
The default values of the uncertainty components represent typical pressure
measurement uncertainty specifications (see Section 1.2.2.1). These values are
based on all Q-RPT based product lines with a confidence of 95%. This means
that, taken individually, there is a good chance that the uncertainty of a given
Q-PRT is lower than default. All values represented in Table 13 can be modified
in the product.

Caution
There are multiple components that make up the product
uncertainty portion of the uncertainty function. It is
recommended that Technical Note 8050TN11 be used for
guidance.

OPERATION
Uncertainty not available in Basic Interface, see Remote, Section 6.5.4, PRR Command
For Advanced Interface, see Section 7.2.7.3.