Options DF-150E 25
CAUTION
Do not use an upstream valve to control flow if the analyzer is
operating on a pump.
7.9.1 Pump Control
An on-board pump can be controlled by the Pump Switch located behind the
door.
The following two options are not available on CE marked analyzers:
If factory configured, an on-board pump can be controlled via a remote switch
wired to the PUMP connector on the back panel.
OR
If factory configured, a remote pump can be powered and controlled by the
Pump Switch located behind the door.
See page 45 for additional information.
7.10Isolated 4 to 20 mA Output
The optional 4 to 20 mA output is proportional to the oxygen reading of the
analyzer. The output of a three range analyzer will be scaled to the “selected”
range.
An output of 4mA represents an operating analyzer with zero detected oxygen.
Outputs ranging from 4 to 20 mA represent oxygen concentrations from zero
to the top of the currently selected range.
The 4 to 20 mA output is electrically isolated from all other analyzer outputs,
and from chassis (Earth) ground.
The maximum load resistance is 1K Ohms. The analyzer provides a loop
supply of approximately 28 VDC.
7.11Gas Scale Correction Factor
The analyzer is factory calibrated to measure oxygen in a background gas of
nitrogen. If the background gas has a lower molecular size and weight than
nitrogen (as does helium or hydrogen) the concentration of oxygen reported by
the analyzer will be greater than the actual concentration. This effect occurs
because the oxygen molecules can more easily diffuse through a low molecular
weight gas (and reach the measurement electrode) than through nitrogen. The
scale factor option allows the analyzer to automatically correct the oxygen
reading for this background gas effect. Correspondingly, if the background gas
has a higher molecular size and weight than nitrogen the concentration of
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