A dirt filter (26) for filtering the fertiliser solution is located in the fertiliser line of a dosing channel.
Using a rotameter (27), the fertiliser suction can be checked and the dosage valve adjusted. The
adjusting of dosage valves is primarily of importance for fertiliser solutions, and not so much for
acid or lye solutions. Partly for this reason, a dosing channel for acid or lye does not have a rotameter.
A dosage valve (29) and a non-return valve (29) are installed in the fertiliser, acid or lye lines just
before the venturi. The control software pulses the dosage valves to control the open time, based
on a recipe and EC and pH measurements. The time that the dosage valves are open and closed
determines the flow rate of fertiliser, acid or lye that is dosed on average.
Various types of dosing channels are available. The type and number of dosing channels on the unit
is customer-specific and is determined during the purchasing process.
EC and pH sensors
The electrical conductivity of the irrigation water is a measure of the fertiliser concentration and is
measured using EC sensors (19) on the branch. The optional line (20) serves to minimise the drop
in pressure across the EC sensors. The pH sensors (21) measure the pH value of the irrigation water.
The pH sensors are located in a sensor holder that is connected to the branch line with a thin line
to eliminate the disruptive influence of the pump pressure.
By using two EC sensors and two pH sensors, the control software can compare the measured values
of the two sensors. If the measured values differ excessively from one another, the control software
signals that one of the two sensors is not working (correctly) and automatically stops the unit in
order to prevent crop damage.
In order to remove the sensors safely, e.g. for maintenance purposes, the line between the manually
operated valves (16 and 24) can be isolated with these valves and made pressureless via the drain
taps (22 and 23) near the pH and EC sensors. These drain taps can also be used to empty the line,
e.g. if the unit is taken out of operation for a longer period of time due to a period of freezing
temperatures.
Cabinet
On a standalone system, the cabinet (33) on the unit contains the whole process computer. If the
cabinet on the unit is a substation of a process computer, the process computer communicates with
the electrical components in the cabinet via the network (Connext) or via direct I/O connections
(Compass). Depending on the model, various other connections (34) are available in the cabinet, e.g.
for the mains supply, irrigation valves, a flush valve or sensors.
Frequency controller
In order to guarantee constant pressure to the crop, a frequency controller (35) may be used. The
frequency controller controls the speed of the pump based on the pressure at the outlet of the unit
which is measured by a pressure transmitter (36). If a frequency controller is not used, the pump is
only switched on or off by the process computer.
EC pre-control
If drain water is reused, an EC pre-control can be used. The pre-control consists of two valves (38)
that are contra-controlled by a common motor. The further one valve closes, the further the other
opens and vice versa. In this respect, one valve allows drain water (with a high EC value) to pass and
the other fresh water (with a low EC value). The EC value of the mixed water is measured by a separate
EC sensor (39). The control software controls the motor on the valves so that the supply water has
a constant, desired EC value. For effective control, the EC values of the drain water and clean water
must differ by at least 0.5 mS/cm.
In order to disassemble the EC sensor safely, e.g. for maintenance, it can be isolated with the manually
operated valves (40). To prevent the mixed water from flowing back into one of the supply lines,
there is a non-return valve (37) in each supply line.
Post-filtration
To prevent blockages in the distribution system, an automatic self-cleaning filter (41) can be used
after the unit. The self-cleaning filter suctions the deposited dirt out of the filter mesh, without the
filtering process being interrupted. The rinse water is discharged via the drain line (42). If not already
present on the unit, a non-return valve (43) must be installed behind the filter. If non-return valve
(43) is present on the unit, non-return valve (13) is not required.
17NutriJet - user - 00.002
Product description
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