HYDROPONIC SYSTEM
-
SOILLESS CULTURE
What a soilless culture is?
Soilless culture is a technology for growing plants in nutrient solutions (water
containing fertilizers) with or without the use of an artificial medium (sand,
gravel, vermiculite, rockwool, perlite, peatmoss. coir, or sawdust) to provide
mechanical support.
Type of soilless culture
There are different types of soilless culture that we can classified in:
- Aggregate culture (hydroponic)
- Water culture
- Aereoponic
Aggregate Culture (hydroponic)
A hydroponic system consists of growing plants with a nutrient solution of
water without soil.
The water with nutrients are contained in a separate tank and they must be
delivered to the plant roots.
The plant roots are closed in a container with a substrate of inert material
(perlite, sand, wood, rockwool, etcetera) to have a mechanical support.
In the substrate are captured the nutrients of the plants and the substrate
must have pores for gas exchange.
To deliver water to the plant root there is an emitter of water of a drip
irrigation system.
Water usually is recycled.
Water culture
The water culture is of the simplest method of soilless culture to create on a
small scale.
The plants and the water with nutrient are in the same container.
In fact in this system the plant roots are totally immersed in a nutrient
solution.
VINCENZO MORELLI
VA elettrotecnica
So this system has different disadvantages: the large amount of water and the
need to aerate the solution continuously.
The system must be composed of support system for the plant, of a system to
aerate the solution and of a system to protect the plant from the sunlight (to
prevent the growth of algae).
The tray can be composed of concrete or wood or plastic.
Its size is usually from 6 to 12 inches deep and 2 or 3 feet wide.
The plants are put in the pores of a wooden cover that floats on the surface of
the solution.
Aereoponics
The aeroponic system is similar to hydroponic system, the only difference is
the substrate: in the aeroponic system there isn't a substrate of inert
material.
This system is composed of a tank of water with nutrient and a different
container where there are the plants.
The plant roots haven't got mechanical support because there isn't the
substrate and an irrigation system delivers the spry water to the plants root
to give them nutrient.
Electronic circuits measure temperature, ph, moisture to permit the correct
growing of the plants.
All systems of soilless culture are of high technology and very expensive. So
their use isn't very diffuse. But these systems are important to permit the
growing of plants in inert areas to improve the life of many people.
VINCENZO MORELLI
VA elettrotecnica
History
The first applications of soilless culture dates back to the 20s thanks the
research of the Californian Gericke.
This technology was used by the US Army to supply fresh vegetables to the
troops during the Second World War in some Japanese islands of the Pacific.
Then the system wasn't used because it was composed of materials very
expensive.
Since the '80s thanks to the continuous scientific research of the
Netherlands, England and Japan the technology of hydroponics was diffused
with the use of new cheap plastic
Now other Countries are studying
disadvantages and diffuse them.
these
systems
to
resolve
some
Interesting is a research program that was introduced by NASA to develop a
system of food production to be used in space missions.
SENSORS
The pH meter
The ph meter consists of a probe that detects a potential difference between
the sides of a membrane by the difference of concentration of hydrogen ions.
A pH units corresponds to 0,059V.
Glass electrode combined
The probe of pH meter is a particularly probe
called glass electrode combined.
The solution separates into OH- and H+.
Based on the concentration difference between H+
of the substance under test and the reference is
determined the pH of the solution.
If the substance is acidic, there will be an
accumulation of H+ on the surface layer of the
membrane,
otherwise
there
will
be
an
impoverishment.
VINCENZO MORELLI
VA elettrotecnica
The pH meter is composed of a
voltmeter showing values in pH scale
In fact an operational amplifier
amplifies and converts the low
electric potential of the probe in pH
units and shifts it of 7 units.
HUMIDITY TRASDUCER
Humidity transducers detect the relative humidity.
The relative humidity is given by the following relationship: U% = Uabs/Usat
where:
- U% = it is the relative humidity;
- Uabs = it is the absolute humidity (it indicates the value of water in a cubic
meter of air);
- Usat = it is the moisture saturation (it indicates the maximum value of water
in a cubic meter of air prior to condensation).
Humidity transducers are based on the relative humidity through the variation
of some electrical quantities such as capacitance and resistance.
The moisture meters are also called hygrometers because they are made with
hygroscopic materials whose dielectric constant depends on the relative
humidity.
The faces of the dielectric are covered by a layer of gold and they are
protected by a plastic casing. On the plates of the capacitor are soldered the
two leads.
The electrical quantity that varies is the capacity, so you cannot work in direct
current but it is necessary to generate a signal that oscillates at a certain
frequency.
Oscillator can be realized in two different ways: with an OPAMP (operational
amplifier) or with the integrated circuit NE555.
VINCENZO MORELLI
VA elettrotecnica
Oscillator by OPAMP
The input voltage V+ will be given by the voltage divider
because the two resistors R1 and R2 are in series (I =
0). So the capacitor will charge to have V+ = V-. Then
the Vcc output becomes -Vcc and the capacitor will
discharge again.
In the end you will get an oscillating signal:
Oscillator by NE555
VINCENZO MORELLI
VA elettrotecnica
Interior of a NE555:
If Vc = 0 then R=0 and S=1  Q=0  The BJT is cut off and the capacitor
discharges
If Vc = 2/3ofVcc then R=1 and S=0  Q=1  The BJT is saturated and the
capacitor charges.
The conductivity meter
The conductivity meter is the instrument that detects the electrical
conductivity of a substance.
The electrical conductivity of a substance is the ability of the substance to
conduct electric current: so the electrical conductivity is inverse to the
resistance.
There are two types of conductors: conductors of first species and conductors
of second species.
Metals are conductors of the first species because they allow the passage of
electric charges (electrons) and don’t allow the transport of mass.
The aqueous solutions are conductors of the second species because they allow
the passage of electrons and positive ions too. So in this case there is also the
transport of mass.
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VA elettrotecnica
If you immerse two electrodes subjected to a certain potential difference in
an electrolytic solution, in direct current the ions will migrate to opposite
poles. So with high voltage could be transformation of material caused by the
phenomenon of electrolysis.
In alternating current the electrolysis doesn’t change the materials because
the reactions are created and reverse.
Measures the electrical conductivity of solutions consist in measuring the
alternating current resistance of the solution, because the passage of charges
and mass does not alter any characteristics of the solution.
These conductivity measurements are carried by a bridge structure:
Kohlrausch bridge. It is similar to Wheatstone bridge but it is in alternating
current.
In this system there is a cell with the solution to be analyzed.
The value of the conductivity is given by the inverse of the resistance of the
immersion cell composed of two electrodes of 1cm2 separated by 1cm.
To have measurements precise they must be performed at the temperature
standard of 20°C or 25°C.
Kohlrausch bridge
VINCENZO MORELLI
VA elettrotecnica