Varian 947, Руководство по эксплуатации и обслуживанию

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Models 947, 948 and 960 Leak Detectors Operations and Service Manual
3-4
This feature is useful when a product specification is more
than one decade less stringent than the sensitivity of the
leak detection system as it is configured. If the configured
system is capable of detecting 10
−
9
atm cc/sec but the test
specification is only in the 10
−
7
atm cc/sec range, then
setting the RANGE STOP to
−
08 reduces the test cycle time
by eliminating the need for the leak detector to reach its
most sensitive decade (10
−
9
) during each test cycle.
AUTO CAL Used to perform an automated calibration based upon the
parameters set. Calibration is compared to a known internal
leak.
To perform an automated calibration, press the AUTO CAL
button, or assert calibrate input via the serial port or
optional discrete I/O.
CALIBRATED
LEAK VALUE The 947/948/960 is shipped from the factory with a
calibrated leak. Its value is noted on the turret of the leak
detector and on the Cal Leak Certification. When a
calibration is performed, the system compares the leak rate
signal with the stored value. The tuning process involves
independently scanning the ion source chamber voltage
and the variable focus voltage, and optimizing each value
for a maximum helium signal. Once the tuning process is
complete, the system gain is adjusted to bring the leak
detector into calibration.
ZERO The ZERO function reads the background leak rate signal,
stores the reading in memory, and then resets the zero
reference point. Subsequent actual test measurements
include both helium from the real leak and helium from
background conditions, however, the recorded background
signal from the measurement is subtracted and the resultant
real leak rate is displayed. To perform a ZERO function,
press the ZERO button, or assert ZERO input via serial port
or optional discrete I/O.
NOTE
Performing the ZERO function while introducing
helium to the test object can result in the suppression of
a real leak. Only use the ZERO function after the helium
source has been removed.