
Chapter 4. Optional Display/User Interface
24
DewPro<Superscript>® MMR31 Installation & Operation Manual
4.4.2
Moisture Measurement Functions
Table 6:
Function
Location
Description
Display
Current
Process Value
VH 00
This location displays the current process humidity value measured by the instrument.
The units of measure for the displayed value (i.e., % RH, dew point or units selected
under
VH 01
) is selected in position
VH 01
. The bar graph beneath the numeric display
represents the position of the current value within the range programmed for the
selected units of measure.
Select Units of
Measure for
Display
VH 01
This location selects the units of measure to be used for the humidity value display. The
available options are:
0 =% relative humidity (Default)
1 = °C dew point
2 = °F dew point
3 = grams/m
3
4 = grams/kg dry air.
Loop #1
at Fault
VH 07
This location specifies the state of current output #1, corresponding to the detection of a
fault with either the humidity sensor or the measurement circuitry. The available options
are:
0 = –10% (3.6 mA)
1 = 110% (22 mA) (Default)
2 = Hold at previous level
Display the
Moisture
Frequency
VH 08
When this location is selected, the A/D counts from the moisture measurement circuit
are displayed.
4.4.3
4-20 mA Output Range Functions
Table 7:
Function
Location
Description
Range of
Humidity
Values
VH 10
% RH 4mA (Default: 0)
VH 11
% RH 20mA (Default: 100)
VH 12
°C dew point 4mA (Default: –15)
VH13
°C dew point 20mA (Default: +85)
VH 14
°F dew point 4mA (Default: 5)
VH 15
°F dew point 20mA (Default: 185)
VH 16
grams/m
3
4mA (Default: 1)
VH 17
grams/m
3
20mA (Default: 350)
VH 18
grams/kg dry air 4mA (Default: 1)
VH 19
grams/kg dry air 20mA (Default: 830)
Pressure
Constant
Adjustment
VH 30
This location allows the user to enter a value for the process pressure. The value is
entered in mmHg. This value is used only for the calculation of the unit grams/kg dry air.
(Default: 760)
Calibrating the
Current Output
VH 38
VH 39
These locations are used to calibrate the 4 mA and 20 mA hardware settings of the
humidity output current loop. This output comes calibrated from the factory and should
not normally need adjustment. To check the setting, connect an ammeter in series with
the negative (
–)
power terminal for loop #1 (see
“Wiring Configurations with One
VH 38
. The output will automatically
change to the 4 mA setting. Adjust as necessary using the
+
and
–
keys. Move to
location
VH 39
. The output will automatically change to the 20 mA setting. Adjust as
necessary. Move to any other matrix location to return the output to normal operation.
If the matrix input is locked (
VH 89
), the calibration values are displayed, but the current
output is unaffected.
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