DH Instruments PPC4, Operation And Maintenance Manual

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PPC4™ OPERATION AND MAINTENANCE MANUAL
© 2009 DH Instruments, a Fluke Company Page 22
function of the resolution and short term stability of the on-board barometer rather than its
absolute measurement uncertainty. This additional uncertainty is ± 1 Pa (0.00015 psi).
3.2.5 Multiple Internal and External Q-RPTs
A base PPC4 pressure controller includes a high precision, utility pressure sensor whose
range is equal to the controller’s range. The utility sensor is not intended to serve as a
pressure reference for low uncertainty measurement. It is for indication, pressure control,
system safety and maintenance functions only.
To obtain low uncertainty, traceable pressure measurement, PPC4 uses Quartz Reference
Pressure Transducers (Q-RPT). Up to four Q-RPTs can be included in a PPC4 pressure
controller/calibrator system. One or two Q-RPTs can be built into the PPC4, up to two may be
located outside the PPC4 enclosure, in an RPM4 reference pressure monitor (one or two in the
RPM4). Once the Q-RPTs available to a PPC4 system have been set up and identified, their
use is managed by PPC4 transparently to the operator.
The use of multiple Q-RPTs, combined with PPC4’s infinite ranging capability and AutoRange
feature (see Section 2.3.7), make it possible for a single PPC4 pressure controller/calibrator
system to cover an extremely wide range of test ranges and measurement modes with low
uncertainty in each range.
Communication between an external RPM4 and a PPC4 controller is by RS232 connection
from PPC4’s COM2 port. One common pressure connection can be made between the
PPC4 and RPM4 pressure ports (see Section 2.3.6 for information on setting up a PPC4 with
external RPM4). RPM4 Q-RPT modules’ SDS function protects RPM4 Q-RPTs from
overpressure when they are not in use.
The PPC4 RPT function (see Section 4.5.12 for Basic Interface and Section 5.7.1, RPT
Search, for Advanced Interface) is used to identify Q-RPTs available to the PPC4. The PPC4
then manages the internal and external Q-RPTs transparently to the operator, selecting the
appropriate Q-RPT for the range of operation and operating valves to connect and disconnect
them as needed.
Each Q-RPT has a default range, which is its maximum range. It can also be downranged
using PPC4’s AutoRange function.
The PPC4 internal pneumatic layout for handling its utility sensor and one or two Q-RPTs
depends on the number of Q-RPTs and their type (Axxx absolute, Gxxx gauge, BGxxx bi-
directional gauge). Figure 32 provides pneumatic schematics of the different PPC4 internal
utility sensor and Q-RPT configurations with a chart of valve status for various operating conditions.

Caution
•
Before operating PPC4 with external Q-RPTs, check carefully that the
RPM4’s Q-RPT TEST(+) port(s) is/are connected to the PPC4 TEST(+)
port. If an external Q-RPT is NOT connected to the PPC4 TEST(+) port,
it will NOT measure the pressure generated by PPC4 and PPC4 may
reach a pressure higher than the target pressure before its watchdog
function recognizes that the external Q-RPT is not connected (see
Section 3.2.21.1). The PPC4 watchdog function monitors differences in
the change in pressure indicated by an active, external Q-RPT and the
PPC4 Hi utility sensor or Q-RPT (watchdog). If the difference becomes
excessive, control is aborted, an audible warning sounds and a
warning is displayed. If this occurs, make sure the PPC4 and RPM4 Q-
RPT TEST(+) ports are connected together and try again.
•
RPM4 with Q-RPT full scale spans below 14 MPa have SDS self defense
system to isolate and protect the Q-RPTs. If an external RPM4 SDS
pressure rating is less than the PPC4 maximum pressure then a
warning will be displayed on the PPC4 front panel when the RPM4 is
detected. In addition, AutoRanged ranges greater than the SDS rating