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Models 947, 948 and 960 Leak Detectors Operations and Service Manual
3-22
RANGE STOP
The RANGE STOP feature configures the 947/948/960 so that it
only auto-ranges down to the pre-selected decade entered in the
range stop variable field. For example, if RANGE STOP is enabled
and set to
−
07, then the most sensitive range that the leak detector
displays is 10
−
7
.
This feature is useful when a product specification is more than one
decade less stringent than the sensitivity of the leak detection sys-
tem 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 parame-
ters 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 pro-
cess involves independently scanning the ion source chamber volt-
age 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.