E C O P H Y S I C S Calibration
CLD 780 TR / July 2000 84
6.2 Performing a calibration
6.2.1 Calibration using a gas diluter
There are commercially available precision gas calibrators which are ca-
pable of diluting calibration gas flows of 1 - 20 ppm by 50 - 500 times
with zero air to allow a multiple-point calibration to be performed. If no
zero air generator is available, synthetic air or zero air from a pressur-
ized cylinder must be used. Connections and operating procedures are
described in the operating manuals of the respective calibrator. The gas
must enter the cal. gas inlet of the PLC 762 photolytic converter at atmos-
pheric pressure. Therefore, the calibration gas line has to be provided
with a bleed line where excess flow is vented through tubing (>1m long)
via a T-connector attached to the cal. gas inlet on the PLC 762.
Note: To avoid the possibility of back flow of atmospheric air into the in-
strument the excess flow should be 50% of the required flow through the
instrument (1.5 l/min). For all tubing inert materials are essential e.g. PTFE
or PFA. For the tubing from the higher concentration NO calibration gas
bottle to the calibrator the manufacturers usually recommend the exclusive
use of stainless steel tubing with a small inner diameter.
6.2.2 Single point calibration (”Span Check“)
After connecting the calibration gas supply to the analyzer, proceed as
follows:
1. Selection of measurement mode:
– Press ”MENU“ key
– Select ”Mode“ and confirm the selection with ”YES“
– Select the required measurement mode
–NO
– NO.c
– NO and NO.c, or
– NO and NO
2
– Confirm with ”YES“.
– Return with ”MEAS“.
2. Selection of measurement range:
– Push ”RANGE“ key
– Toggle with ”NO“ to the desired range and confirm the selection
with ”YES“
– The cursor is now underneath the field for the integration time inter-
val. Enter Integration time (0.1 - 600 sec.) and confirm with ”YES“.
– Return with ”MEAS“.
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