DH Instruments PPCH, Руководство по эксплуатации и обслуживанию

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3. OPERATION
Page 25 © 2009 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 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 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 3.3.8.2).
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
tolerance reading
3.3.6).
Reservoir level low
Ten brief beeps (see Section 3.5.7.3.2).
3.2 GENERAL OPERATING PRINCIPLES
3.2.1 PRESSURE CONTROL PRINCIPLES
Numerical references in this section refer to Figure 9.
PPCH is designed to precisely generate, measure and control liquid pressure into a volume
connected to its
TEST
port (13). Pressure is measured by a utility sensor or one or two
Quartz Reference Pressure Transducers (Q-RPT)(15, 18).
Pressure is generated internally using a hydropneumatic pump(19). The hydropneumatic
pump uses the ratio of two pistons to transform low pressure drive air into high pressure
liquid output. The drive air pressure is controlled by an internal pressure regulator(3).
The liquid supply to the pump is from an internal or external reservoir. Liquid returned from
the test system when reducing pressure is returned to the internal or external reservoir via a
return tube that provides a constant fluid level when the system is vented. Provision is made
for filling, draining, returning liquid to and viewing the level of the internal or external reservoir
(6, 7,8,9,10) (see Section 5.6). Should the system be run with the reservoir empty causing
the pump to draw air and lose its prime, the internal reservoir can be pressurized to reprime
the pump(4, 5) (see Section 5.10.1).
The hydropneumatic pump high pressure output supplies a servo-controlled inlet valve(17).
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 liquid