Operation
Range Menu
Thermo Fisher Scientific
Model 42
i
Trace Level Instruction Manual
3-11
The auto range mode switches the NO, NO
2
, and NO
x
analog outputs
between high and low ranges, depending on the NO
x
concentration level.
The high and low ranges are defined in the Range menu.
For example, suppose the low range is set to 50 ppb and the high range is
set to 100 ppb (
Figure 3–6
). Sample concentrations below 50 ppb are
presented to the low ranges analog outputs and sample concentrations
above 50 ppb are presented to the high ranges analog outputs. When the
low range is active, the status output is at 0 volts. When the high range is
active, the status output is at half of full-scale.
When the high ranges are active, the NO concentration must drop to 85%
of the low NO range for the low ranges to become active.
In addition to each channel having two ranges, each channel has two span
coefficients. 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 NO range is set to 0–50 ppb and the high
NO range is set to 0–200 ppb.
Figure 3–6.
Analog Output in Auto Range Mode
Auto Range Mode
