Panametrics DewPro MMY30, Руководство пользователя, Страница: 29 / 43

DewPro
®
MMY30 User’s Manual 21
Chapter 4. Optional Display/User Interface (Option G or H)
4.5.2 Special Calibration
4.5.2.1 Adjusting the Pressure Constant
4.5.2.2 Adjusting the Current Loop Hardware at 4 mA
4.5.2.3 Adjusting the Current Loop Hardware at 20 mA
VH 30 The process pressure constant is entered in bar (absolute), 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 compressing 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
scaled to a total pressure of 1 bar. An elevated process pressure above 1 bar requires compensation 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, by using a pressure regulator in a
bypass system. Default: 1 bar (absolute)
VH 38 By connecting an ammeter in the loop, the correct current value (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.
VH 39 Selection of this field assists during calibration, generating a nominal 20 mA signal. However, the actual
value must be 21.92 mA, an over range value to a dewpoint reading of 22°C. By connecting an ammeter
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.