Zeroing Example; Flow Example - Ametek 303B User Manual

Zeroing Example

By supplying a zero-moisture calibration gas, the analyzer may not dry
down to 0. If the analyzer stops drying down at 3.2 ppm, an offset of 3.2
can be entered to have the display read 0.0. This is probably the most
common use for the offset factor.
If the analyzer later dried down below 3.2 ppm, the display would flash
indicating that the value is negative. For example, to get a 0.0 reading if
0.3 were flashing, offset must be changed from 3.2 to 2.9.
Refer to page 5-8 of this manual to change offset parameter.
Flow Compensation Example
The analyzer requires a 100-mL flow to operate properly, but if the pro-
cess can supply only a 50-mL flow, gain can compensate. For example, the
reading is 112.0 ppm at a 100-mL flow; when flow is reduced to 50 mL,
56.0 is displayed. To show the correct moisture, gain can be in-creased
from 1.0 to 2.0, causing the display to increase back to 112.0 ppm.
The same can be applied in reverse. For a 4.75 lb/mmscf reading at 100mL/
min, and increasing the flow to 200 mL flow, 9.50 is displayed. To display
the correct moisture, gain can be decreased from 1.0 to 0.5, caus-ing the
reading decrease back to 4.74 lb/mmscf.
Change the 4 to 20-mA Output Range Example
These examples change the 4 to 20-mA output, but the display will not
show the correct ppm readings.
For example, if you want to have readings from 50 to 100 ppm be mapped
into the 4 to 20-mA output at 0 to 100 percent, gain must first be changed
from 1.0 to 2.0. This changes the ppm readings from 50 to 100 to 100 to
200. Then, by changing offset from 0.0 to 100.0, the readings change again
from 100 to 200 to 0 to 100. Then, simply set the 4 to 20-mA range to 0 to
100; the 50 to 100 ppm readings then will be 0 to 100 percent of the 4 to 20-
mA output. As stated earlier, 0 to 100 ppm will be displayed even though
the real moisture levels are 50 to 100 ppm.
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