Operation
Range Menu
Thermo Fisher Scientific
Model 48
i
Instruction Manual
3-11
Table 3–3.
Default Analog Outputs in Dual Range Mode
Channel
Connector Pin
I/O Terminal Pin
Description
1 14
1
CO
High
Range
2 33
3
CO
Low
Range
3 15
5
None
4 34
7
None
5 17
9
None
6 36
11
None
Ground
16, 18, 19, 35, 37
2, 4, 6, 8, 10, 12
Signal Ground
Note
All channels are user definable. If any customization has been made
to the analog output configuration, the default selections my not apply.
▲
The auto range mode switches the CO analog outputs between a high and
low ranges, depending on the concentration level. The high and low ranges
are defined in the Range menu.
For example, suppose the low range is set to 50 ppm and the high range is
set to 100 ppm (
Figure 3–6
). Sample concentrations below 50 ppm are
output based on low range selection and sample concentrations above 50
ppm are output based on high range selection. 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 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 0–10000
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
Auto Range Mode
