5.4
The Level Control System
5.4.1
Overview
The purpose of the level control system is to reset the evaporation pan water
level back to its reference level at a regular time each day. You can set the
reset time to suit your project. This replicates the operation of a manual
evaporation pan, and produces similar data. After operating for 24 hours the
water lost to evaporation is replaced from a tank or other water supply. If the
pan is overfull from rainfall the excess is pumped from the pan. This can be
recycled back to the supply tank if site water is scarce.
The pan water level recorded by the data logger is used to control the reset.
At the specified time the logger will decide if water is to be added or
removed. It then switches on the appropriate device until the reference level is
reached. If the pan is in danger of overflowing from heavy rainfall the pan
will also be reset.
A level control module consisting of a switch card in a polycarbonate
enclosure controls the reset. This switch card is operated by the site
MICROLOGGER or by an associated STARLOGGER or PROLOGGER.
This card has relays with the capacity to operate either solenoids or small
pumps. Either device may be used depending on the site. Power is supplied
by a solar powered battery system. A regulator on the switch card manages
battery charging. All devices connect to the row of pluggable terminals
located at the front of the enclosure.
Automatic Evaporation System
INSTALLING THE EQUIPMENT 25
5.4.2
Level Control Module
This self contained instrument is normally located near the battery and
solenoid or pump. There are no internal settings or adjustments. A cable
connects it to the site data logger terminals.
The other components of the system plug into the marked terminals.
A Test terminal socket is provided. This has continuous 12V power. Plug in
your fill or drain device if you want to test run it.
Contact your local UNIDATA support centre for advice if you wish to fit the
controller to an existing instrument, or use it for another purpose.
5.4.3
Fill System
A solenoid valve is normally used to turn on a water supply and add water to
the evaporation pan. This is typically turned on by the data logger at 0900
each day, if the water level is low and turned off when the level is correct.
The solenoid is located in the base of the instrument enclosure. The outlet of
the solenoid is connected to the evaporation pan by a 12.5mm (½”) hose. This
hose enters the pan above water level to avoid any chance of water siphoning
back out of the pan.
UNIDATA
26 INSTALLING THE EQUIPMENT
Fill system
Drain system
Battery
Test power
Power from solar panel
Power for GSM MODEM
Signals from site data logger
1
16
TOP
