19
PROPORTIONAL CONTROL MODE
The user can vary three different parameters, i.e. the setpoint
(S1 or S2), the deviation (D1 or D2) and the proportional
control mode period T
c
from 1 to 30 minutes. Duration of
the activated control is directly proportional to the error value
(Duty Cycle Control Mode): as the measurement approaches
setpoint, the ON period diminishes.
The following graph describes the pH process controller
behavior. Similar graph may apply to the mV controller.
During proportional control the process controller calculates
the relay activation time at certain moments t
0
, t
0
+T
c
, t
0
+2T
c
etc. The ON interval (the shaded areas) is then proportional
to the error amplitude.
For example with S1 representing High Setpoint
Setpoint (S1) = 7.00 pH
Deviation (D1) = 1.00 pH
T
c
= 1 minute
If measurement > 8.00 pH, then ON all the time.
If measurement = 7.60 pH, then ON for 36 seconds
OFF for 24 seconds.
If measurement = 7.10 pH, then ON for 6 seconds
OFF for 54 seconds.
The number of strokes per minute of the pump can be
changed only by means of the pump’s command.
Referring to the following diagram (low setpoint) the relay is:
• ALWAYS ON if pH < setpoint-deviation;
• ON proportionally to the error
if setpoint - deviation < pH < setpoint
ON
OFF
14
Se
Hysteresis
Setpoint
t
0
t
0
+T
c
t
0
+2T
c
t
0
+3T
c
