25
SOLAR PUMPING
Guidelines - Electrical design and installation
of solar pumps
Pressure transmitting probes
The probe (see figure 19) is placed in the lower part of the tank and measures
the water level (accuracy is 1 cm) according to the pressure it undergoes:
the higher the water level above the probe will be, the more pressure there
will be. The probe transmits the same information as the sliding float probe
(fluctuation of the output current), and can be interpreted by the same type
of display.
Like electrode probes, pressure-transmitting probes are suspended in the
tank. If it is not fixed, it will «swirl» during refills and this will damage the
cable at the point of attachment. It must therefore be attached to a support:
a suspended stainless steel cable with a weight, or a vertical bar fixed in the
tank.
Mind: minimum and maximum height of water must be specified when ordering the probe to the supplier, in order to ensure
the minimum current (4 mA) at minimum level, and maximum current (20 mA) at maximum level of water (Manufacturer
settings).
DISPLAYS FOR POTENTIOMETRIC PROBES
Potentiometric probes (or «4/20 mA») are to be connected to display units provided for this purpose. These displays are
generally compact (see figure 20), and they necessitate a setup, especially to know the shape of the tank (cubic, horizontal
cylinder, vertical cylinder, or other). A display has at least the following functions:
• Ensure the power supply of the probe (12 or 24V DC to be specified to supplier)
• Calculate the quantity of water in the tank in m3 depending
on the water pressure, and the set tank shape and size.
• Send some signals (free-volt contacts)
based on defined thresholds
FIGURE 20:
TYPICAL DISPLAYS
Hitec Brand
Afriso /
Eurojauge Brand
Interjauge Brand
Potentiometric probes have many advantages: high reliability over time, accurate measurement of the level and display in m
3
,
option of automatic start / stop, remote reporting of alarms... they nevertheless have a major disadvantage: they must be
electrically powered.
It usually consists of a small solar panel of 50W dedicated to the probe, and a small box with a charger and two batteries of
7Ah (size of a motorcycle battery or a UPS for desktop) to ensure a continuous power supply, no reset of settings. The display
is generally attached to the front of the cabinet.
This power supply is not complex to implement, however there is no standard cabinet to perform this function. The box must
be custom-made by the supplier.
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