I have finished drawing the circuit diagrams for the quad photodiode boxes. Here are copies of the circuit diagram.
There are three main operation circuits in the quad photdiode box: a summing circuit (summing the contributions from the four inputs),
a Y output circuit (taking the difference between the input sums 3+2 and 1+4), and an X output circuit (taking the difference between the
input sums 3+4 and 1+2). I will complete an mini report on my examination and conclusions of the QPD circuit for the suspension wiki tomorrow.