Water treatment controllers are used in Water Treatment to maintain the water at the quality required. It does this by measuring parameters like conductivity pH, ORP and chlorine in real-time and bringing them closer to the desired value by using actuators that could be a dosing pumps or bleed-off valve.
You may notice though that, at times, in spite of using the best controller and dosing pump, the parameters you wish to control are fluctuating wildly above and below your set point.
This is one factor that you might have missed:
In choosing a water treatment controller, it is important to understand the 3 different types of control – ON/OFF Control, Proportional Control and PID control. Choosing the wrong type of control may either compromise on your treatment quality or incur unnecessarily high cost.
Here are the differences between the three control types:
1. On/Off Control
• The actuator works at full capacity regardless of the deviation from the set point until the set point is reached, at which point it is completely turned off.
• On/off control is suitable if the actual reading just needs to be below or above the setpoint but not the best choice if you need the water to be within range of a setpoint.
• Example: bleed-off of solenoid valve based on the actual conductivity value.
• The on/off control can result in frequent open/close of the bleed-off valve. Using the hysteresis function can help to reduce the fluctuation.
2. Proportional Control
• Better control than ON-OFF control. The actuator operates at between 0% and 100% depending on how far the actual value is from the set point.
• Limitation of proportional control is steady state error, in which the final control output is always above or below the setpoint.
• If the steady state error still lies within your acceptable tolerance range, then proportional control is a good enough control system for your application
3. PID Control
• More efficient control of water treatment process requires PID control. PID control, which stands for proportional-integral-derivative, uses a closed-loop feedback mechanism to control process variables.
• The control algorithm improves control by projecting the current rate of change to the future, and adjust the actuator accordingly in anticipation.
• As a result, the actual value will straddle along the set point very tightly. For example, if your acceptable chlorine or pH tolerance range is very small, then you will need to use the PID control.
In conclusion, the type of control you need depends on the application and how well you need to control the water quality. Once you have determined the control type you need, the next step would be to select the water treatment controllers that have the control type you are searching for.
Autoflo Technology are able to provide controllers with all three control types. The Injecta Nexus Controller are designed to work well with Injecta range of metering pumps (Athena, Taurus and Atlanta) for the accurate dosing of chemical..
