Split-Range Control

Understanding split range control

Split-range control involves a single controller sending signals to two (or more) control valves or actuators, which then modulate different parts of the process. This is particularly useful in scenarios where a process variable, like temperature, needs to be maintained within a specific range using different methods for heating and cooling

Example: Temperature Control

Consider a fermentation tank in a brewery where the temperature must be kept within a narrow range. If the temperature drops too low, a heating element is activated to warm the tank. Conversely, if the temperature rises too high, a cooling system is engaged to lower the temperature. In this case, the cooling system uses a different process then the heating system. Sometimes it ‘works’ to use one set of PID gains, but often this leads to issues with tuning or instabilities. Therefore it is advised to use a split-range controller, where if the output of the PID drops below 0 (indicating that cooling is required), the PID gains are adjusted to the optimal values for the cooling process.

Implementation of a split-range controller

Figure 1 shows a typical example of how a split-range controller can be implemented. Our Dotx PID Controller includes this feature. It is important to note, that when a gain schedule is used, that the PID controller should be implemented in a way that allows a bumpless transfer.

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