When all the sensors are open, the voltage found in the output of the block (across the load) is determined by Px. This control can adjust the output for voltages between 1.25 and 25 V.
When any sensor is closed, the voltage changes to a value determined by the adjustment of the corresponding variable resistor. For instance, when X1 is closed, the output voltage falls to a value determined by the value of P1 and Px in parallel.
The LM350 must be mounted on a heat sink, and the input voltage must be at least 3 V higher than the maximum programmed voltage in the output. This block can be controlled by a drum position sensor as described in the Section 9.2, on theory. Many blades can make contact with a drum (cylinder) where the voltages are programmed according to the position. Another suggestion is the use of a microcontroller for this task.
