Product Manual

Reference to past charts makes it possible to maintain the most desirable soil moisture content in each
section, year after year. The charts are a very important factor in IRROMETER irrigation control, and
it is strongly recommended that they be kept up to date.
The charts are also useful to keep rainfall information, fertilizer applications and unusual weather
conditions posted with moisture readings for future reference.
Use of dataloggers makes such record keeping easy and automatic. IRROMETERS are available with
electronic outputs for use with datalogging equipment.
Taking Readings
The frequency of charting readings depends upon how fast the soil dries out. In sandy soils or in hot
weather, readings should be charted two or three times a week. In moderate climates, charting
readings once a week is usually adequate. Even less frequent readings may be required in wet
weather. After a few irrigation cycles, the charts will indicate how often readings are required in each
section. It is best to chart the readings just before and just after an irrigation so that the maximum and
minimum readings are recorded.
In areas where there are extreme daily fluctuations in temperature, readings should be taken the first
thing in the morning. Especially during peak water use, readings can climb during the day and then
drop back at night. Thus, early a.m. readings are usually most accurate. Tap the gauge lightly before
taking a reading. The slight movement of the pointer will indicate whether the soil is drying out or
soaking up moisture.
Usually the instruments are “serviced” on the same round that readings are taken. Readings should
always be taken before servicing.
Field Servicing
It is normal for the fluid level just below the reservoir to fall as the soil dries out. A vacuum is created
in this space. Following an irrigation, this vacuum draws moisture back out of the soil causing the fluid
level to rise almost to its original level by the time the
gauge reading indicates field capacity. However, with
each cycle a little air is drawn in from the soil and collects
below the reservoir. This air slows up response of the
instrument to variations in soil moisture. It also tends to
result in slightly lower than accurate readings.
The purpose of “servicing” tensiometers is to remove the
entrapped air in order to maintain optimum accuracy.
Servicing is simple with IRROMETERS. Loosening the
cap allows air to escape by bubbling up out of the
reservior, whose water then drains back down to refill the
instrument body. Fluid in the reservoir should be replaced
as necessary. The instrument will not hold the same water
it was installed with; it will have to be periodically refilled.
Unscrew the cap slowly with a slight downward pressure,
whenever there is a high vacuum reading on the gauge,
so that the pointer does not slap back against the stop,
causing shock to the gauge.
The large cap and resilient stopper make control of this operation easy
.
To re-seal, it is not necessary to exert excessive pressure to get a positive seal with this closure. The
resiliency of the stopper can be prolonged by tightening the cap only about
1
/4 turn after the stopper
makes contact with the bottom of the reservoir. If the stopper hardens, replace with a new stopper.
When relatively moist soil conditions are maintained, very little air is drawn into the instrument and the
supply of fluid in the reservoir usually lasts for several months. Where very high gauge readings occur
,
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