Proportional Control Mode
The Proportional Control mode is recommended only for small bodies of water to prevent overfeeding from oversized feeders. In this mode, the outlet relay is turned ON and OFF at a rate that decreases as the set-point 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 set-point (see schematic).
Proportional control operates only within the defined Progressive Zone, 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.
This control mode is available in Proportional Control only, it provides more precise control than ON/OFF control and reduces overfeeding, particularly in smaller bodies of water.
In all three automatic control modes (ON/OFF, Proportional and 4-20 mA), the controller uses a deadband zone near the set-point to prevent chattering of the relay. The deadband is expressed as a percentage of the set-point value and can be adjusted by the operator on the DEADBAND screen.
With the deadband, the outlet remains activated until the sensor reading reaches the set-point, at which point it is deactivated. In order for the relay to be re-activated, the reading has to get outside the deadband, thus eliminating the effect of small fluctuations.
The PROGRESSIVE ZONE is a control zone around the set-point where the outlet activation depends on how far the sensor reading is from the setpoint (see schematic above). If the sensor reading is outside of the zone, then the outlet is turned on 100% of the time. The activation rate then decreases progressively as the reading nears the set-point value. It reaches 0% when the reading enters the deadband zone near the set-point.