DH Instruments PPC4, Operation And Maintenance Manual

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3. OPERATING PRINCIPLES
Page 37 © 2009 DH Instruments, a Fluke Company
(see Section 3.2.11) have their own, specific limits. Negative gauge mode and the BA100K
Q-RPT also have a lower limit.
Automated pressure control targets greater than the upper limit or lower than the lower limit
are not accepted. When the pressure measured by PPC4 exceeds the upper limit or lower limit,
automated or direct manual pressure control is aborted and an intermittent warning beep sounds.
The Upper Limit most often protects the device or system connected to the PPC4 TEST(+)
port from accidental overpressure.
Note
The default upper limit is 105 % of AutoRanged span or 102 % of Q-RPT
default (maximum) range, whichever is lower. The default lower limit is
- ATM, except with a BGxxx Q-RPT in which the default lower limit is the
negative equivalent of the upper limit. The default lower limit of a BA100K
is 66 kPa (9.6 psi).

Caution
Upper limit values are specific to each range and measurement mode. Be
careful not to assume that the upper limit set in one measurement mode
will apply to the other.
For example, if 150 kPa is selected as the upper limit in gauge mode, the
upper limit will not be 150 kPa in negative gauge mode of the same range.

OPERATION
For Basic Interface, see Section 4.4.4.
For Advanced Interface, see Section 5.7.8.1.
3.2.21.1 Over Pressure Function
In addition to the UL function, PPC4 has an over pressure function.
The over pressure function executes when a Q-RPT measures a pressure that is
104 % of its default span or a utility sensor measures a pressure that is 110 % of
its default span. BG15K Q-RPTs also have a negative over pressure limit.
The BG15K Q-RPT negative over pressure limit is - 17.5 kPa (- 2.3 psi).
When PPC4 is using an external Q-RPT in an RPM4, the PPC4 utility sensor or
Hi Q-RPT acts as a watchdog. If the watchdog measures a pressure greater
than the maximum pressure of the active external Q-RPT, PPC4 executes the
overpressure function.
The over pressure function causes all pressure control to be interrupted and
disabled, changes the active range to the default range of the Internal, Hi (IH) Q-RPT
or utility sensor and causes the measured pressure display to flash. If the
Q-RPT is a Gxxx or BGxxx, the
TEST(+) / TEST(-) bypass valve is opened. The
overpressure function also logs the time and date of the overpressure condition in
both user and factory logs to assist in incident diagnosis (see Section 3.2.27.5).
To recover from an overpressure condition, correct the overpressure condition
and cycle PPC4 power. Be sure to correct the condition that caused the
overpressure before cycling power.