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Span Check
Thermo Fisher Scientific
a percent of the upper range limit (URL) of the recorder or as the current
full-scale setting of the analog output.
Zero Drift (%) = ((A
Where A
is the recorder response obtained for this test, Z is the recorder
0
response obtained for zero air at the last calibration, URL is the upper
range limit of the recorder, and Zero Drift is expressed as % of full-scale.
In this case, there is no need to convert the analog signal to units of
concentration. For example, if the instrument is configured for a 0-10 volt
analog output, the output at the last zero adjustment was 0.1 volts and the
output during this zero check is 0.3 volts, then the zero drift could be
calculated as follows:
Zero Drift (%) = ((0.3 volts – 0.1 volt)/10 volts) X 100
Zero Drift = 2.0 %
To run a span check, press
lower left corner of the display. The internal span valve will open, and if
the span gas is plumbed as suggested, span gas will flow to the manifold or
sampling line. The unit must be allowed to stabilize for at least five minutes
before taking data.
As discussed elsewhere, the flow rate of span gas must be greater than the
flow demand of the inlet system. In addition, the calibration system must
be configured so that the span gas is being delivered at atmospheric
pressure. For most applications, the span check should be run with a CO
concentration that is approximately 80% of the instrument's current range
setting. The simplest and most reliable source of span gas is a cylinder
containing the span concentration of CO in air that has been certified
against an SRM or CRM.
If the span check data is recorded directly from the front panel or from the
digital interface (RS-232/485), the span drift can simply be reported in
units of ppm, or as a percent of the actual span concentration. If regulatory
requirements call for span drift to be reported as percent of range, the
calculation will be made based on the range specified in the regulations.
If the data is being collected with a strip chart recorder attached to one of
the analog outputs, the span error is typically reported as a percent of the
upper range limit (URL) of the recorder. In this case, record the analyzer's
response in % of scale as A
following equation:
– Z)/URL) X 100
0
until the word "SPAN" appears in the
, and compute the span error from the
80
Model 48i Trace Level-Enhanced Instruction Manual
Calibration
Periodic Zero and Span Checks
4-13
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Troubleshooting
