GE DewPro MMY30, User Manual

Page: 30 / 47

The Optional Display/User Interface (Option G) 4-5
November 2005
Display and Output Mode
(cont.)
5.
Selecting the Analog Output Span (20 mA)
Caution!
Ensure the value in VH11 is always at least 20 °C above the
value assigned to 4 mA.
6.
Setting the Span Value for the ppm
v
Range
Special Calibration
7.
Adjusting the Pressure Constant.
Location
in Matrix Description of Function
VH
11
The dewpoint value corresponding to the analog output
span (20 mA) is entered here. Default: +10°C.
Location
in Matrix Description of Function
VH
12
Selection of this field sets the span value for the ppm-v
range. Default: 100.
Note:
The offset is always 0 ppm
v
. Do not exceed 1000
ppm
v
.
Location
in Matrix Description of Function
VH
30
The process pressure constant is entered in bar (abso-
lute), which is used to calculate ppm
v
. The moisture
unit ppm
v
is the ratio of water vapor pressure to the
total process pressure and is, therefore, independent of
the process pressure. The reason is that when com-
pressing a gas (process pressure) all partial pressures
increase by the same factor (Dalton's Law).
The gold/aluminum oxide sensor is selective to water
vapor pressure monitoring a higher vapor pressure
when the total pressure (process pressure) increases.
The formula utilized by the analyzer refers to the total
pressure of 1 bar. An elevated pressure of the process
has to be corrected by programming the actual process
pressure in bar absolute to the matrix field VH 30.
The system should be designed to maintain a constant
pressure, for instance, by using a pressure regulator in
a bypass system.
Default: 1 bar (absolute)