Table of Contents
Advertisement
2.3 Navigating the front panel
2.3.1.2 Sensitivity
2.3.1.3 Input filter
2.3.1.4 Equivalent Noise Bandwidth
SR124 Analog Lock-In Amplifier
by the [Input] button. Each successive press of [Input] steps from A,
6
to A–B, to I (10
), to I (10
Input coupling can be switched between AC and DC by pressing
[Couple]. (ICPL, 4 – 12 )
The outer (shield) terminal of both input BNCs are tied to each other
and can be set to Float (through 10 k ) or Ground (through 10 ) by
pressing [Ground]. (IGND, 4 – 12 )
Overloads at the preamplifier stage are indicated by the red OVLD
indicator in the signal input block.
The overall gain of the SR124 is controlled by setting the sensitivity.
Full scale sensitivities from 100 nV to 500 mV, in 1–2–5 steps, can be
selected by turning the SENSITIVITY knob. (SENS, 4 – 13 )
Overloads in the AC signal path, after the preamplifier but before the
phase sensitive detector, are indicated by the red OVLD indicator in
the sensitivity block.
The input filter type is selected by pressing [Type]; selections cycle
from Band Pass, High Pass, Low Pass, Notch, and Flat. (TYPF, 4 –
12 )
The filter Q-factor can be adjusted between 1 and 100 by turning the
Q-factor knob. (QFCT, 4 – 12 )
The tuning frequency of the filter is adjusted by turning the large
INPUT FILTER knob. This knob responds with velocity sensitivity,
so turning the knob more quickly will span larger frequency ranges
quickly. The frequency setting is displayed on the numeric display,
with either Hz or kHz illuminated. (IFFR, 4 – 12 )
When operating the input filter as Band Pass or Notch type, and at
high Q-factor, it is often necessary to trim the input filter performance.
Pressing INPUT FILTER cycles the knob's focus between the main
frequency tune, a (dimensionless) trim o set of the frequency (f trim),
and a notch depth adjust (depth ). When adjusting f trim or depth,
the units annunciators (Hz and kHz) are both o . (IFTR, 4 – 12 )
For Gaussian noise, the equivalent noise bandwidth (ENBW) of a
filter is the bandwidth of an ideal rectangular filter which passes the
8
), and then back to A. (ISRC, 4 – 11 )
2 – 13
Advertisement
Table of Contents
