3. OPERATION
Page 53 © 2002-2007 DH Instruments, a Fluke Company
If the current measurement mode is negative gauge or the Q-RPT is a BA100K, there is also a
lower limit. The display is:
1. Entry field for upper limit value.
2. Entry field for lower limit value and active range pressure unit
of measure and measurement mode indication.
Upper:104.00 IH
Lower:-110.00 kPa g
Edit the upper and lower limit values as desired. Use the cursor control keys to move
between the two edit fields. The lower limit must be a negative value. Press [ENT] to return
to the MAIN RUN screen with the new upper and/or lower limit active. Press [ESC] to return
to the MAIN RUN screen with no change to the limits.
When the upper or lower limit has been exceeded, the display of current pressure flashes
and a buzzer sounds for 3 seconds at 2 second intervals. Reduce pressure using direct
pressure control keys or an automated pressure command to return to normal operation.
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 you set 150 kPa as the upper limit in gauge mode, the upper limit will not
be 150 kPa in negative gauge mode of the same range.
Upper limits are always specified and displayed in the current pressure unit except for
altitude units. When in altitude units, upper limits are expressed in kPa if the altitude
unit is meters (m) and psi if the altitude unit is feet (ft).
3.4.4.1 OVER PRESSURE FUNCTION
In addition to the UL function, PPC3 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 PPC3 is using an external Q-RPT in an RPM4, the PPC3 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, PPC3 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 3.5.9).
To recover from an overpressure condition, correct the overpressure condition
and cycle PPC3 power. Be sure to correct the condition that caused the
overpressure before cycling power.
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