DH Instruments PPC4, Руководство по эксплуатации и обслуживанию

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3. OPERATING PRINCIPLES
Page 35 © 2009 DH Instruments, a Fluke Company
3.2.18 Leak Test

PURPOSE
To run an automated leak check routine that determines the leak rate of the system
connected to the PPC4
TEST(+) port.

PRINCIPLE
Leaks in the system connected to PPC4’s TEST(+) port can cause differences between the
pressure measured by the PPC4 Q-RPTs and pressure in other parts of the test system.
A large leak can cause the PPC4 to be unable to set and control pressures reliably.
The LEAK CHECK function is provided as a means of checking and quantifying the leaks that
may be present in the system.
The principle of the LEAK CHECK function is the measurement of the natural decrease or
increase of pressure in a fixed volume over time. The LEAK CHECK function allows a leak
check time to be set. The total pressure change and the average rate of change over the leak
check time are calculated and displayed.
Note
•
Changing the pressure in a test system causes adiabatic temperature
changes in the gas that need to disipate before a valid leak
measurement can be made. In general, a 30 second to 1 minute wait
before running a leak check is adequate to allow the adiabatic
temperature change to dissipate and valid leak measurements to be
made. However, stabilization time may be much longer with larger
volumes, higher pressures or with liquid test media.
•
As a general rule, the maximum acceptable leak rate for optimal PPC4
automated pressure control operation and to ensure in tolerance
measurements with default pressure control parameters is 0.5 % of current
range span/minute.
•
Leak check is range specific in the sense that leak check is run using
the active range. However, only one set of leak check results is
maintained in memory and each leak test completed overwrites the
memory. View leak check always shows the results of the last leak
check run regardless of the range that is now active. The results
screen includes the range indicator to indicate the range in which the
leak check was run.

OPERATION
For Basic Interface see Section 4.5.11.
For Advanced Interface see Section 5.7.3.2.
3.2.19 Resolution

PURPOSE
To set the resolution with which measured pressures and other pressure indications and
settings are displayed.

PRINCIPLE
The resolution with which PPC4 displays pressure values can be adjusted. This feature can
be used to reduce the resolution when lower precision measurements are being made and
excess resolution might confuse or distract the operator.
The resolution setting determines the number of digits with which pressure is displayed.
The resolution is calculated based on the full scale of the range and then rounded to the