GE MOA 280i, Руководство по эксплуатации и обслуживанию

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GE Analytical Instruments ©2006 DLM 14291 Rev. A
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connections for the frit restrictor, gas sampling package or vacuum pump or a
problem with the ozone generator or electronics.
If the NO cal gas is not turned on when a calibration is performed, a warning
screen indicating that the NO is lower than the zero gas will be displayed. Check
that the NO cal gas is turned on and excess gas is flow out the open leg of the tee.
Calculation of Gas Concentration
To calculate the concentration of NO in a gas sample, the NOA reads the PMT
signal from the Analog to Digital converter, subtracts the offset and then multiples
by the response factor. If the calculated value is less than zero, the NOA will
display a value of <0.0 ppm or <0.0 ppb. If the display shows a <0.0 reading, this
indicates that the offset value is too large and the instrument must be
recalibrated.
Because the offset is subtracted from the PMT signal, the range of the NOA will
always be less than 1000 ppb for high sensitivity, and less than 500 ppm for low
sensitivity. The maximum signal for the ppb range can be calculated using the
formula ( 4095 - ppb offset) X ppb scaling. When the signal from the PMT exceeds
the maximum signal, the NOA will display the greater than sign (>) and the current
maximum value. For example, if the ppb offset is 20 and the ppb scaling is .24,
the maximum value that can be measured is 978 ppb. If the sample contains a
higher concentration of NO, the display and outputs, will show greater than 978
ppb. .
Independent Calibration of ppb and ppm Ranges
For NO standards that contain <1 ppm NO, or if accurate standards in the ppb
range can be prepared, the ppb range can be calibrated independent of the ppm
range. In most cases, there is no advantage in independently calibrating the ppb
range. The best method for preparing ppb level standards is to use mass flow
controllers to dilute ppm level NO standards with zero air. For low ppb standards,
a two-stage dilution is usually required. For example, a setup can be done with a
1:100 dilution of a 10 ppm NO standard with zero air to prepare a 100 ppb
standard, and then dilute this gas 1:10 with zero air to prepare a 10 ppb standard.