When using Auto Zero the zero gas cylinder must be connected at all times
4.4 Span Adjustment
Before a Span adjustment is made ensure that the gas cylinder is connected and that
the correct pressure is set. See section 2.7.3.
It is recommended that zero adjustment is done immediately prior to adjusting span.
For multi-gas analysers, it is convenient if the span gas used is a mixture containing an
accurately known concentration for each of the gases measured. If this is not practicable, then
the span process must be repeated for each gas in turn, using the appropriate span gas.
4.4.1 Setting Span
Select 'Span Adj.' on the main menu. The span screen will be displayed, and the span gas will
be connected to the analyser(s). The readings will change to reflect the span gas.
Verify that the flow meter shows adequate flow – span adjustment cannot be made if the flow
is incorrect. If necessary, make small adjustments to span gas pressure to correct the flow.
Wait for the gas reading(s) to stabilise.
If the readings are satisfactory, press ‘< Main’ to return to the main screen without making
changes. – Or ->
Press the key labelled with the appropriate
gas. The display will ask you to set the
correct gas value. The value offered is that
last used, but if necessary use the Gas + and
Gas - keys to set a value that agrees closely
with the span gas concentration.
Press ‘Set Span’. The microprocessor will
then reset the reading to the value entered. If
the change is to great and the processor is
unable to reset the span, a warning message
will appear on the screen.
If the span adjustment fails, carefully check
the span gas cylinder. If possible, verify the gas concentration on a second analyser, or try
another bottle of span gas. If the span fails and the span gas is correct, contact ADC
(Spares & Service) Ltd., or their local authorised agents for service.
Figure 12 - Setting the span gas
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