Guide to choosing the right dosing mode for your system.
Sequential Dosing (default ON)
This causes the dosing pumps or valves to activate in sequence, one after the other and allows high current valves or pumps to be connected to the unit without fear of overloading the controller or its power adapter.
If in doubt about the current required to drive the pumps then always select sequential dosing. If 3 or more nutrient parts are selected sequential dosing is enforced to avoid damage to the controller.
By selecting sequential dosing, the dosing outputs will operate in sequence, one after the other. This allows a small power supply to be used with dosing devices that draw a heavy current. For example, small peristaltic pumps typically draw 1.2 Amps or so at 24V DC.
If three-part dosing was used and three pumps were allowed to come on at the same time the power supply would need to be rated at about 4 or 5 Amps.
By selecting sequential dosing a 2Amp supply could be used.
Proportional Dosing (default OFF)
Proportional dosing allows rapid dosing toward the set point by varying the dose size in proportion to the error. It is useful when you want the tank to dose up quickly.
If this is selected then both a maximum and minimum dose time must be specified. The maximum time should be set so that a dose of this size would raise the EC from its raw water value to 80% of the setpoint value in a single dose.
The minimum dose time should be set to achieve a rise in EC of 0.1mS/cm (CF=1, ppm=50). The controller will then select the most appropriate dose size within this range depending on the measured EC.
The controller then looks at the size of the error and if large gives large doses but as the EC or pH setpoint is approached, the controller will give smaller and smaller doses approaching the minimum size.
For instance when starting with a tank of pure water, the controller will make one very large dose followed by smaller and smaller doses as the setpoint is approached.
This is useful in irrigating (drip) systems that do not re-circulate as it allows rapid dosing after each irrigation occurs.
This feature is not available with more than 2 part mixes.