Stanford Research Systems SR844, User Manual

Page: 80 / 246

3-22 CH2 Display and Output
SR844 RF Lock-In Amplifier
Key features and parameters for the various displayed quantities are shown below.
Quantity
[Unit]
Display
Range
Bar
Graph
Range
Ratio Offset Expand Max
Sample
Period
Y [Volts]
±
110% f.s.
±
f.s. Yes
±
110% f.s. Yes 22
µ
s, Note 4
θ
[Deg]
±
180
°
±
180
°
Note 2 Note 3 Yes 88
µ
s, Note 4
Ynoise
[Volts]
±
110% f.s.
±
f.s. Note 1 No Yes 1.953 ms,
Note 5
Ynoise
[dBm]
±
220 dBm
±
200 dBm Note 1 No No 1.953 ms,
Note 5
AUX IN 2
[Volts]
±
10 V
±
10 V No No No 88
µ
s, Note 4
Note 1 If ratio mode has been selected, the reciprocal of the appropriate input
(1.0V/AUX IN 1 or 1.0V/AUX IN 2) is computed, and
both X and Y are
multiplied by this quantity.
θ
is computed from Y/X and is unchanged by
the ratio. Ynoise will be scaled in the same proportion as Y.
Note 2 If ratio mode has been selected, the reciprocal of the appropriate input
(1.0VAUX IN 1 or 1.0V/AUX IN 2) is computed, and
both X and Y are
multiplied by this quantity.
θ
is computed from Y/X and, except for sign, is
unchanged by the ratio. The phase will change by 180
°
if the ratio input is
negative.
Note 3 The detection phase may be modified by adjusting the Reference Phase; this
can be used to adjust or null the displayed phase of the input signal, but it
also modifies X and Y (and their offsets). There is no separate phase offset
adjustment.
Note 4 This shows the worst-case output sample rate for the CH2 analog output.
The sample rate is fastest at the high end of an octave band. See IF
frequency display in the Reference Section for more details.
The X output updates 4 times slower when 18 and 24 dB/oct filtering is
used.
The digital display is always updated at a 2 Hz rate. The bar-graphs are
updated at 64 Hz. Display quantities may be read out via remote interface
or stored in the internal data buffers (see Chapter 4,
Data Storage ) at a
maximum rate of 512 Hz.
Note 5 The noise is computed at 512 Hz for all time constants
≤
30 ms. For longer
time constants the noise is updated 25.6 times per time constant.
Offset
User entered offsets can be added to X and Y. These offsets are added before taking
ratios, output time-constant filtering, and computing R and
θ
.