there is a single input coming from a temperature sensor, but then two controller outputs, or actuators, being used to change the temperature. PID can output both positive and negative values, so this example uses a case structure to decide when each actuator will be used. Let’s say that output channel 1 is connected to a heater and output channel 2 connects to a fan for cooling the system. If the PID output value is positive, then we want to raise the temperature by writing the output value to the heater and turning the fan off by writing a zero to channel 2. However, if the PID output value is negative, the false case structure writes the output value to the fan, and a zero to output channel 1. This is a very common way of implementing PID with multiple outputs.