Figure 3-6. Analog Output In Auto Range Mode - Thermo Scientific 48i Instruction Manual

Operation
Range Menu
When the high range is active, the concentration must drop to 95% of the
low CO range for the low range to become active.
In addition, each CO analog output has a span coefficient. There are two
span coefficients so that each range can be calibrated separately. This is
necessary if the two ranges are not close to one another. For example, the
low CO range is set to 0–50 ppm and the high CO range is set to 0–1000
ppm.
Note When using auto range mode, the high and low ranges should not
vary by more than 1 order of magnitude. For instance, if the low range is
set to 20 ppm, then the high range should be set to no more than 200
ppm. This is because the concentration response is non-linear and it is
possible that the low range readings could become unpredictable above the
top of the low range, resulting in a substantial jump in concentration
readings when switching between ranges. One possible fix for this would be
to perform the 3-point calibration (via the Service menu) on both ranges
and make sure that the low range high point matches or is greater than the
high range low point. This will ensure that the high and low range
concentration curves will overlap. If both of these methods are
unacceptable due to local regulations, then the dual range mode should be
used so that the range selection may be evaluated by the user to meet their
reulations. ▲
Figure 3–6. Analog Output in Auto Range Mode
Thermo Fisher Scientific Model 48i Trace Level-Enhanced Instruction Manual 3-11