Chemtrol PC3000 - Chapter VI - Maintenance; Controller and Sensor Maintenance

MANUALPC-2010 CHAPTER IV - OPERATION Page 48
X.1.3 - Automatic Control
In the Automatic Control Type, the operator can choose
among two different Control Modes: ON/OFF or, as shown on
Submenu X.1.3.
X.1.3.1 ON/OFF Control
In the ON/OFF Control mode, the controller activates the
control outlet until the setpoint is reached, at which point it is
turned off. It is turned on again when the reading is outside of
the deadband.
Selection of the ON/OFF control mode leads to the
DEADBAND submenu screen X.0.1 discussed above.
X.1.3.2 Proportional Control
T
he Proportional Control mode is recommended only for small
pools and spas to prevent overfeeding from oversized feeders.
In this mode, the outlet relay is turned ON and OFF at a rate
that decreases as the setpoint is neared. The rate goes down
from 100% ON in a 100-second CYCLE TIME at the edge of
the Progressive Zone to 0% at the setpoint (see Figure 30).
Proportional control operates only within the defined
Progressive Zone (see Submenu X.0.2 on previous page).
Outside the zone, control reverts to standard ON/OFF mode.
The wider the Progressive Zone is, the more slowly and
precisely the controller will return to the setpoint. As the width
of the Progressive Zone is decreased, the reaction becomes
faster and faster until eventually, one gets near the conditions
of ON/OFF control.
It should be noted that longer time limits may be required to
account for the slower effective feed rates.
X.1.3.3 - 4-20 mA Control
In the special option for “4-20 mA" Control Mode, the controller
sends an electronic signal output from 4 to 20 mA that is
proportional to the distance from the setpoint. A 4 mA output
corresponds to 0% feed rate, 12 mA to 50% and 20 mA
corresponds to 100%. The values of the 0 and 100% limits are
adjustable for each function.
This type of control requires a device - usually an electronic
feed pump – with a linear response to output currents.
X.1.4 - Timer Control
In the Timer Control mode, the controller activates the control
outlet according to fixed ON and OFF cycles (in minutes),
regardless of sensor input. This allows programmable metered
operation in case of sensor failure.
It can also be used to feed a supplementary oxidizer, as in the
Automated Chloramine Treatment (ACT) process.
S
ubmenu X.1.3
Figure 30 - Proportional Feed Rate
Submenu X.1.3.3
Submenu X.1.3.3.1
Submenu X.1.4
AUTOMATIC CONTROL
ON/OFF
Proportional
4-20 mA
TIMER CONTROL
Cycle ON (min) 0.1
Cycle OFF (min) 1.0
4
-
20 mA Control
ORP
SANITIZER
pH
CONDUCTIVITY
TEMPERATURE
4
-
20 mA LIMITS
ORP Top (mV) 850
ORP Bottom (mV) 650