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iGrow 1800 Installation Guide
Page77
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04 Irr04 Irr
Input
Soil5
Threshold
0.0%
VWC
OffTime 00:00 hh:mm
The third and final screen is where you select the trigger sensor and the threshold for turning on the
irrigation valve. The threshold is a Volumetric Water Volume (VWC) percentage. It corresponds to an
input of 0 to
x
Volts DC.
The
OffTime
is the maximum off time that you will permit. If the threshold is not reached by the end of
this time, the irrigation valve will be turned on as though the threshold was reached. This is a backup
position in case the sensor is not operating correctly or was inadvertently removed.
Vapor Pressure Deficit (VPD) Irrigation
Vapor pressure deficit (VPD) is the difference (referred to as deficit) between the amount of moisture in
the air and how much moisture the air can hold when it is saturated. Therefore,
VPD = VP(SAT) – VP(Air)
The iGrow 1600/1800 calculates the VPD based on the temperature and humidity sensors in the
greenhouse.
04 Irr04 Irr
Mode:
VPD
hr mm ss
OnTime: 00:00:00
The first screen is where you set the valve
OnTime
once the VPD threshold is reached.
04 Irr04 Irr
Start
__at__
09:00A
End at 07:00P
VPD
This second screen is where you set the time window during which you will allow the irrigation valve to be
triggered. If the VPD threshold is reached outside this time window, the irrigation will be triggered at the
start of the time window. Both the start and stop times can be fixed times by selecting the
at
option or
they can be based on Sunrise and Sunset.
04 Irr04 Irr
Threshold
0.00
inHG-Hr
Max Off 00:00 hh:mm
The third and final screen is where you select the VPD threshold for turning on the irrigation valve. The
threshold is an accumulated pressure measurement input as in HG-Hr .