Block Diagram - Stanford Research Systems SR865A Operation Manual

Chapter 2
Thus, in the previous example with a 2 V pk–pk square wave input, the SR865A would
detect the first sine component, 1.273 sin(ωt). The measured and displayed magnitude
would be 0.90 V (rms), e.g. 1.273/√2.
Degrees or Radians?
In this discussion, frequencies have been referred to as f (Hz) and ω (2πf radians/sec).
This is because people measure frequencies in cycles per second and math works best in
radians. For purposes of measurement, frequencies as measured in a lock-in amplifier are
in Hz. The equations used to explain the actual calculations are sometimes written using
ω to simplify the expressions.
Phase is always reported in degrees. Once again, this is by custom. Equations written as
sin(ωt + θ) are written as if θ is in radians mostly for simplicity. Lock-in amplifiers
always manipulate and measure phase in degrees.

Block diagram

A simplified block diagram of the SR865A's lock-in circuit is shown below and
explained in the following sections.
Basics
SR865A DSP Lock-in Amplifier
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