A loss monitor is a device which detects these secondaries and generates a signal whose amplitude increases with the number of particles detected. Position errors are not the only possible cause for beam loss. If the beampipe aperture is too small or the beam size is too large the beam may not be able to get cleanly through the aperture regardless of its position. Furthermore, even if beam easily fit in the aperture and was centered on that aperture everywhere in Switchyard, losses would still be inevitable at the splitting stations where beam comes into contact with the septum wires as part of the splitting process. The loss monitor itself is a chamber made up of an inner conductor and an outer conductor with Argon-CO2 gas filling the space in between.
High voltage is applied to the outer conductor.
When particles enter the chamber and ionize the gas a current is created which flows between the two conductors. As long as there is a current signal going to the integrator, the capacitor in the feedback loop of the op-amp charges up. In other words, as more particles go into the chamber the voltage on the integrating capacitor increases. Most loss monitors are calibrated so that there is an increase of 1 volt on the readback for every 5E9 particles of detected beam loss. However, at a certain point the level of the voltage readback can go no higher due to limitations in the digitizing process.