GE DewPro MMY31 Installation And Operation Manual page 14

DewPro MMY31
SPECIAL CALIBRATION
7. Adjusting the pressure constant
Location in Matrix
VH 30
8. Adjusting the Current Loop at 4 mA
Location in Matrix
VH 38
9. Adjusting the Current Loop at 20 mA
Location in Matrix
VH 39
GE General Eastern
Installation and Operation Manual
Description of Function
The process pressure constant is entered in bar (absolute), which
is used to calculate ppmv. The moisture unit ppmv 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 compressing a gas (process pressure) all partial
pressures increase by the same factor (Daiton's Law).
The gold/aluminum oxide sensor is selective to water vapour
pressure monitoring a higher vapor pressure when the total
pressure (process pressure) increases. The formula utilized by
the analyser refers to the total pressure of 1 bar. An elevated
pressure of the process has to be corrected by programming the
actual process pressure 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)
Description of Function
By connecting a mA-meter in the loop, the correct current (4 mA)
can be adjusted by increasing or decreasing the displayed digits.
NOTE: If the matrix input is locked (VH89), the calibration values
are displayed but the current output is unaffected. To enable
adjustments, VH89 has to be unlocked by entering "50" into this
field.
Description of Function
Selection of this field assists during calibration generating a
nominal 20 mA signal, but the actual value must be 21,92 mA, an
over range to a dewpoint of 22 oC.
By connecting a ma-meter in the loop, the correct current (21.92
mA) can be adjusted by increasing or decreasing the displayed
digits.
NOTE: If the matrix input is locked (VH89), the calibration values
are displayed but the current output is unaffected. To enable
adjustments, VH89 has to be unlocked by entering "50" into this
field.
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