FILTERING AND TIME CONSTANTS:
The time constants should be set to as small a valve as possible consistent with required SIN.
The filter settings
on preamplifiers have no effect on final noise levels. These are determined
only by the lock-in time constant and associated noise bandwidth. Therefore,
preamplifier filters must be set to stop only unwanted signals outside
the lock-in bandwidth. This can help prevent overloading of the lock-in.