Stanford Research Systems SR850 User Manual page 120

Gain and Time Constant Menu
Reserve
This key selects either maximum, minimum or manual dynamic reserve.
When the reserve is maximum, the SR850 automatically selects the max-
imum reserve available at the present full scale sensitivity. When the
reserve is minimum, the minimum available reserve is selected. The
dynamic reserve is displayed in the settings display at the top of the
screen (if selected in the DISPLAY/SCALE menu).
When the reserve is manual, the reserve is set by the user to a value
between the min and max reserve. The reserve is set in 10 dB
increments.
Changing the sensitivity may change the reserve. With max or min
reserve, the max or min reserve of the new sensitivity is used. With
manual reserve, the reserve is kept the same relative to the mini-
mum reserve. For example, if the sensivity is 10 mV and the reserve is
21 dB (20 dB above the minimum for this sensivity), changing the sensiv-
ity to 5 mV will change the reserve to 27 dB (20 dB above the 7 dB mini-
mum). If the new sensivity does not have a reserve high enough to satis-
fy this rule, then the max sensitivity will be used instead.
The minimum and maximum reserve limits for each sensitivity are listed
below.
Sensitivity
1 V
500 mV
200 mV
100 mV
50 mV
20 mV
10 mV
5 mV
2 mV
1 mV
500 µV
200 µV
100 µV
50 µV
20 µV
10 µV
5 µV
2 µV
1 µV
500 nV
200 nV
100 nV
50 nV
20 nV
10 nV
5 nV
2 nV
Do not use ultra high dynamic reserves above 120 dB unless absolutely
necessary. It will be very likely that the noise floor of any interfering
5-10
Min Reserve (dB) Max Reserve (dB)
0
6
4
0
6
4
0
6
4
10
16
24
30
36
44
50
56
64
70
76
84
90
96
104
110
116
124
0
6
14
20
26
34
40
46
54
60
66
74
80
86
94
100
106
114
120
126
134
140
146
154
160
166
174