PPCH-G™ OPERATION AND MAINTENANCE MANUAL
© 2007 DH Instruments, a Fluke Company
Page 30
PPCH-G Q-RPTs allow instantaneous switching between gauge and absolute measurements
modes. Any additional uncertainty in gauge measurement mode due to the dynamic
compensation for atmospheric pressure technique is a function of the resolution and short
term stability of the on-board barometer, not its absolute measurement uncertainty.
This additional uncertainty, ± 1 Pa (0.00015 psi), is insignificant in the pressure ranges
covered by PPCH-G.
3.2.5
MULTIPLE INTERNAL AND EXTERNAL Q-RPTS
A base PPCH-G 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, PPCH-G uses Quartz
Reference Pressure Transducers (Q-RPT). Up to four Q-RPTs can be included in a PPCH-G
pressure controller/calibrator system. One or two Q-RPTs can be built into the PPCH-G and up
to two more may be located outside the PPCH-G enclosure in an RPM4 reference pressure
monitor. Once the Q-RPTs available to a PPCH-G system have been set up and identified,
communication with them is managed by PPCH-G transparently to the operator. However,
setting up hardware and following procedures to protect lower pressure external Q-RPTs
from overpressure when higher pressure Q-RPTs are used is the responsibility of the user.
Take precautions not to overpressure external Q-RPTs when using them with a PPCH-G.
When using external Q-RPTs in RPM4s as reference pressure measurement devices with a PPCH-G,
the user is responsible to setting up hardware and following procedures to protect lower range Q-
RPTs from overpressure. Only the Lo Q-RPT (IL) built-into the PPCH-G is protected automatically.
Communication between the PPCH-G and an RPM4s is by RS232 from PPCH-G’s COM2 port.
The PPCH-G RPT function (see Section 3.3.5) is used to identify Q-RPTs available to the
PPCH-G. The PPCH-G then manages communication with the internal and external Q-RPTs
transparently to the operator, selecting the appropriate Q-RPT for the range of operation and
configuring it as specified.
Each Q-RPT has a default range, which is its maximum range. Q-RPTs can also be
downranged using PPCH-G’s AutoRange function.
Before operating PPCH-G with an external Q-RPT, check carefully that the RPM4’s Q-RPT
TEST(+) port is connected to the PPCH-G TEST port. If an external Q-RPT is NOT connected to the
PPCH-G TEST port, it will NOT measure the pressure generated by PPCH-G and PPCH-G may reach a
pressure higher than the target pressure before it recognizes that the external Q-RPT is not
connected (see Section 3.4.4.1). The PPCH-G monitors differences in the change in pressure
indicated by an active, external Q-RPT and the PPCH-G Hi utility sensor or Q-RPT. If the difference
becomes excessive, control is aborted, an audible warning sounds and a warning is displayed. If
this occurs, make sure the PPCH-G and RPM4 Q-RPT TEST(+) ports are connected together and
try again.
Position Identification of Q-RPTs In a PPCH-G System
Position identification of the currently active Q-RPT or utility sensor in the PPCH-G system is
continuously displayed in the upper right hand corner of the PPCH-G’s MAIN RUN screen and
most other screens (see Section 3.1.1). See Table 4 for position designation protocol for the
Q-RPTs available in a PPCH-G system.
See Table 1 for a complete listing of Q-RPTs available and their default ranges.
