DH Instruments PPCH-G, Руководство по эксплуатации и обслуживанию

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3. OPERATION
Page 21 © 2007 DH Instruments, a Fluke Company
3.1.4 REMOTE [ENT/SET P] (FOOT)SWITCH
The optional remote ENTER function is a switch that duplicates the function of the front panel
[ENT]
key. The remote ENTER function is serviced by a connector on the PPCH-G rear
panel labeled
REMOTE ENTER
. An optional footswitch is available to activate remote entry
hands free or a user supplied switch may be used. See Section 7.3 for information on
remote ENTER switch wiring.
The remote ENTER feature can be particularly convenient when running AutoTests
(see Section 3.3.6) in which using a footswitch to
[ENT]
allows hands free operation.
3.1.5 SOUNDS
PPCH-G is equipped with a variable frequency tone device to provide audible feedback and
alarms. The beeper is used for the following indications.
Valid key press
Brief beep. Choice between three frequencies or NO
sound is available (see Section 3.5.5.2).
Invalid key press
Descending two tone “blurp”.
Leak check completed
Three two second beeps (see Section 3.3.9).
Purge routine completed
Three two second beeps (see Section 3.3.8).
Upper limit exceeded
Intermittent one second beeps (see Section 3.4.4)
Active external device not connected
Eight second high frequency beep (see Section 3.2.5)
Pmax! (overpressure limit) exceeded
Eight second high frequency beep (see Section
3.4.4.1).
AutoTest reading in tolerance/out of
Ascending triad/descending triad (see Section 3.3.6).
tolerance reading
3.2 GENERAL OPERATING PRINCIPLES
3.2.1 PRESSURE CONTROL PRINCIPLES
Numerical references in this section refer to Figure 6.
PPCH-G is designed to precisely measure and control gas pressure into a volume connected
to its
TEST
port(8). Pressure is measured by a utility sensor or one or two Quartz Reference
Pressure Transducers (Q-RPT)(11, 13).
A high pressure gas supply is connected to the
SUPPLY
port(16). The supply pressure
transducer(14) measures the supply pressure for system functions. The supply shut-off
valve(15) is always open during normal operation. The supply shut-off valve is a safety
feature to protect agains accidental overpressure in case of loss of electrical power to the
PPCH-G. If the power supply is interrupted during operation, and the servo controlled inlet
valve is open, it will remain open allow pressure to continue to increase. However, loss of
power will cause the supply shut-off valve to close, interrupting flow of high pressure gas
from the
SUPPLY
port.
The high pressure gas supply supplies a servo-controlled inlet valve(12). The inlet valve is a
pressure balanced needle valve whose needle position is controller by a stepper motor and
belt drive. The inlet valve provides very high precision control of the gas admitted to the test
system from the high pressure gas supply. An outlet valve(5) of the same type as the inlet
valve precisely controls gas exhaust to the
VENT
port(6).
The inlet and exhaust valve can adjust and maintain gas flow and therefore pressure rate of
change very precisely. The inlet and exhaust valves are operated in a feedback loop driven
by the pressure measured by the reference pressure transducer or utility sensor(11, 13).