User's Manual

25
e.g. EC proportional control for HI 9913
Setpoint = 2.20 mS/cm (EC)
Measured value = 1.45 mS/cm
Delta = 2.20 - 1.45 = 0.75 mS/cm
Proportional settings = EC set to 1 and time cycle to 60 seconds
The controller will be dosing
fertilizers to increase the EC to
the desired limit. Since it is
0.75/1 = 75% away from
the ideal setting, it will keep the
dosing really activated for 75%
of the time over the predeter-
mined 60 seconds. The terminals
are hence theoretically activated
for 45 seconds and off for 15
seconds.
In order to avoid over dosage of
highly concentrated chemicals or
fertilizers, the controller provides
even a more accurate control.
As the graphs show, it does that
by stopping the dosage as soon
as the current pulse curve inter-
sects the dosage curve. This means
shortening the dosage period if
the chemicals have reacted quickly
or lengthening it if the measured
conductivity continues to drift from
the ideal setpoint as can be seen
from the graphs.
0
SECONDS
mS
2.0 0
90
PROPORTIONAL SETTINGS
0.5 1.5
D mS
Seconds15 30 45
60
0.25
0.50
0.75
1.00
15 30 45 60
D mS
Seconds15 30 45
60
0.25
0.50
0.75
1.00
15 30 45 60
D mS
Seconds15 30 45
60
0.25
0.50
0.75
1.00
15 30 45 60