
green button once to ‘wake up’ the Monitor. The display will show the name you assigned, firmware version and the
battery status. A second push shows the current date and time on line 1. If the start time has not yet been reached,
the start time will be displayed on line 2. If running, the records stored to date will display. Push the green button
again to read sensor input port number 1. Each successive push of the green button will reveal another reading, in
sequence to port 8. The in-field display screen shows the sensor name, type and current reading. After 10 seconds
of inactivity, the Monitor display will go into sleep mode, to preserve battery life. Taking in-field manual readings will
not alter the automatic readings, nor will they be added in to the sequence of readings being stored. Such manual
readings can aid in making on the spot irrigation scheduling decisions, while the stored data is used to view the rate
of change over time and to evaluate the performance of irrigations which have taken place.
SENSOR SELECTION & WIRING — The 900M Monitor comes with seven WATERMARK soil moisture sensors
(200SS-15) and one Soil Temperature sensor (200TS) (Your Monitor may have been ordered with a different sensor
combination). WATERMARKs and Switch Closures can be wired directly into any port on the monitor. Rain
Gauges must be wired to Port 8 only. Temperature sensors should be wired before all WATERMARKs or
set of WATERMARKs. RSU-C or RSU-V IRROMETERs must be wired to an adapter board then can be wired to
any open port. Be sure to mark each pair of sensor wires indicating what type of sensor is attached and the
placement depth. Attach sensor wires to the appropriate terminals as determined by your sensor selection.
The terminal strips have spring tensioned lever terminals. First, insert the wire in the bottom of the terminal,
then push down on the black lever. The lever can be lifted for wire removal, with a finger or small screwdriver
inserted in the slot. Terminals will accept wire up to AWG 16. If a larger size is used, run a short length of smaller
wire to the terminal strip. If all eight ports are WATERMARKS, then the default soil temperature setting for
compensating soil moisture readings will be what is programmed in the SETUP screen, for example 75°F (24°C).
The temperature setting is used to compensate the WATERMARK soil moisture sensor readings for varying soil
temperatures, since temperature affects the accuracy of the reading. If a temperature sensor is used, that
sensor’s reading is then used for the WATERMARK
compensation. Install the temperature sensor on sensor
input port #1, then it will compensate all WATERMARK
sensors installed after it. Or compensate sensors
differently as shown here:
Note: IRROMETER Model RSU transducers require a
wiring adapter, auxiliary power and special instructions,
please consult factory for advice.
An IRROMETER Switching Pressure Gauge can be used for
the Switch Closure sensor input, to record whenever the
irrigation system is running. It stays in the closed position
until the irrigation is turned off, then returns to the open
position as pressure in the pipe drops. This gives you a
data-logged recording of your irrigation system run
time.
Be sure to select a Switching Pressure Gauge with the correct range for the operating pressure of the
irrigation system. The pressure at which the switch closes should be within the middle third of the gauge operating
range. For example, if the irrigation system’s normal operating pressure is 8 p.s.i., then use a gauge with a 0 to 15
p.s.i. range. Also, be sure your sensor reading interval is relative to your irrigation system run time.
MANAGEMENT — The key element in proper soil moisture measurement is the operator. Taking the time to interpret
your sensor readings will give you a vivid picture of what is happening with the soil moisture in the root system of
your crop. Usually 2-3 readings between irrigations is sufficient. The graphical display of your readings show exactly
how quickly (or slowly) your soil moisture is being depleted. Use the following readings as a general guideline:
• 0 – 10 centibars = Saturated soil
• 10 – 30 centibars = Soil is adequately wet
(except coarse sands, which are beginning to lose water)
• 30 – 60 centibars = Usual range for irrigation (most soils)
• 60 – 100 centibars = Usual range for irrigation in heavy clay
• 100 – 200 centibars = Soil is becoming dangerously dry for
maximum production. Proceed with caution!
Your own situation may be unique because of differences in crop, soils and climate. Perhaps the most important
soil moisture reading is the difference between today’s reading and that of 3-5 days ago. That is to say, how quickly
is the reading going up. A slow increase means the soil is drying out slowly. But a big jump means the soil is
losing water very rapidly. By analyzing such trends in the readings, you will determine WHEN to irrigate. By
using sensors at two or more depths in the root system, you can determine HOW MUCH water to apply.
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