Calibration
Zero and Span Check
4-10
43iQHL Instruction Manual
Thermo Scientific
The zero and span check procedure is normally performed any time a quick
check of the accuracy of the instrument is required. Normally, zero and
span are checked daily. As experience is gained with the instrument, the
frequency of these checks can be adjusted accordingly.
The span gas concentration used in the span check should be between 70%
and 90% of the full-scale range. The zero and span drift should be
measured and recorded prior to making any adjustments.
All gas must be supplied to the instrument at atmospheric pressure. It will
be necessary to employ an atmospheric bypass plumbing arrangement to
accomplish this.
If a filter is used, all gas must enter the instrument through the filter.
Use the following procedure to check the zero/span.
1.
If the instrument is equipped with the optional zero/span and sample
valves, connect the zero and span gas to the rear panel bulkheads
labeled ZERO IN and SPAN, otherwise connect a source of vented
zero air to the SAMPLE bulkhead.
Note
Do not use nitrogen for zero air.
▲
2.
To ensure that the zero air is being measured at atmospheric pressure,
check that the flow is approximately 0.9 LPM (zero air flow must be
slightly greater than instrument sample flow).
a.
From the Home screen choose
Settings>Health Check>Status
and Alarms>Flow and Pressure
.
b.
Make sure that the reported sample flow is less than the actual zero
air flow.
3.
Monitor the zero air reading and wait for the reading to stabilize.
4.
Record the measured SO
2
value as the zero drift since the last
adjustment. If the zero has changed by more than ±0.015 ppm, it is
recommended that a new calibration be performed.
5.
Connect a source of vented span gas to the SAMPLE bulkhead. The
span gas should be approximately 80% of the full-scale range.
Zero and Span
Check
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