990 CLD Autoline™ Leak Detector
DRAFT 2/2/04
A-1
Appendix A. Understanding the 990 CLD
Analog Leak Rate Output
Understanding the 990 CLD Analog Leak Rate Output
The 990 CLD leak detection system is designed for wide flexibility in adapting to your
specific leak testing application. As such, the 990 CLD leak detector offers complete
flexibility in adjusting the various controls during process setup to allow direct reading of
the leak rate on the front panel bar graph and exponent display. The leak detector also offers
two types of analog output voltages that track the front panel leak rate display: Linear and
Logarithmic. Each has advantages in particular applications and is described below.
Linear Analog Voltage Output
The accompanying chart labeled Linear Output Voltage (Figure A-1 on page A-5) is useful
in converting from leak rate to output voltage and from output voltage back to leak rate. The
six lines labeled
0
to
6
along the right hand margin represent the six settings of the RANGE
SELECT switch. Note that the output voltage scale along the bottom has been expanded to
aid in reading the lower decades.
This output is derived directly from the leak rate signal. The voltage output is in direct
proportion to the leak rate. Correlated with the front panel display is the setting of the
RANGE SELECT switch (SW7). The output voltage is calculated by multiplying the front
panel leak rate by 10 raised to the RANGE SELECT switch setting. For example, if you are
reading a leak rate of 1 x 10
-3
standard cubic centimeters per second (std cc/sec) on the
front panel bar-graph and exponent display, and the RANGE SELECT switch is set to 2, then
the output voltage is:
(1 x 10
-3
) x (102) = 0.1 VDC
For a leak rate of 1 x 10
-5
std cc/sec with the same setup, the output voltage is:
(1 x 10
-5
) x (102) =0.001 VDC
or 1 mV. Correspondingly, if the leak rate is 10
-1
std cc/sec with the same setup, the output
voltage is:
(1 x 10
-1
) x (102) = 10 0981 DC
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