Stanford Research Systems SR860, Руководство по эксплуатации

Страница: 59 / 222

Chapter 2 Basics 41
SR860 DSP Lock-in Amplifier
Thus, in the previous example with a 2 V pk–pk square wave input, the SR860 would
detect the first sine component, 1.273 sin(
ω
t). 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 SR860’s lock-in circuit is shown below and explained
in the following sections.