DH Instruments PPCH, Руководство по эксплуатации и обслуживанию

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3. OPERATION
Page 29 © 2009 DH Instruments, a Fluke Company
3.2.2.2 DYNAMIC CONTROL
Dynamic control
mode is designed to set the pressure to the target value and
control continuously to keep pressure within the hold limit and as close to the
target value as possible (see Figure 10).
The advantage of this control mode is that the final pressure achieved is the
same as the target value. The maximum value of the control error is equal to the
hold limit. The average value of the control error is generally much smaller than
the hold limit.
During dynamic pressure control, the hold limit is active. If the pressure goes
outside of the hold limit, a
Not Ready condition occurs. See Table 10 for default
hold limit values and Section 3.4.6 to customize the hold limit.
There are two types of dynamic control. Standard dynamic control is the default
type of dynamic control used in most situations. Hi volume dynamic control is
also available for situations in which standard dynamic control cannot achieve a
Ready condition in a reasonable amount of time and/or cannot maintain the
Ready condition once achieved. Hi volume dynamic control may be necessary
when the test volume connected to the PPCH is greater than 100 cc. The
difference between
standard and hi volume dynamic pressure control is in the
use of the thermal pressure controller (TPCU). In standard dynamic control,
control transitions from the control valves to the TPCU before Ready occurs and
the target pressure is reached. In hi volume dynamic control, control is by the
valves only unless they valves are unable to maintain the Ready condition.
Figure 10.
Dynamic pressure control operation
PPCH includes a Ready/Not Ready feature that indicates when current pressure
control requirements have been met (see Section 3.2.3).
With dynamic pressure control active, a Ready condition occurs whenever:
•
The current measured pressure is inside the hold limit.
Figure 11 illustrates Ready/Not Ready operation in dynamic control mode.
In dynamic control mode, normal procedure is to assume that when a Ready
condition occurs (pressure inside the control hold limit), the measured pressure
equals the target pressure. For this reason, when the pressure is Ready in dynamic
control mode, the measured pressure display is equal to the target pressure.