Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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Signal Inputs 2-65
SR785 Dynamic Signal Analyzer
Signal Inputs
The Input Range on the SR785 varies from a maximum of 34 dBV full scale to a
minimum of -50 dBV full scale. A signal which exceeds the current input range will
cause the OverLoad indicator to appear at the top of the screen. A signal which exceeds
the maximum safe range (35 dBVpk) will turn on the Hi V indicator and set the range to
34 dBV.
The Input Range is displayed in dBV. The maximum and minimum range equivalents are
tabulated below.
Max 34 dBVpk
31 dBVrms
50.1 Vpk
35.4 Vrms
Min -50 dBVpk
-53 dBVrms
3.16 mVpk
2.24 mVrms
Manual Range
The fixed Input Range is specified in the [Input] menu. Signals that exceed the range will
overload and become distorted. Signals which fall to a small percentage of the range will
lose dynamic range.
Auto Range
The Input Range can be set to automatically correct for signal variations. Use the
[Auto Range Ch1] and [Auto Range Ch2] keys to toggle Auto Ranging On and Off.
Specify either Normal or Tracking Auto Range in the [Input] menu.
When Normal Auto Ranging is On and an overload occurs, the Input Range is increased
so that the signal no longer overloads. If the signal decreases, the input range is not
adjusted. You must take care to ensure that the signal does not fall dramatically after
pushing the Input Range to a very (high) insensitive setting.
Tracking Auto Range moves the Input Range up when an overload occurs and down
when the signal falls below half full scale.
Auto Range is always Tracking for swept sine measurements.
Input Noise
Noise measurements in FFT analyzers are usually made using Power Spectral Density
(PSD) units. PSD units simply normalize the amplitude of each frequency bin by the
square root of the linewidth. A window correction factor is also included to compensate
for the bandwidth of the different windows. PSD units have the form Vrms/
√
Hz or
dBVrms/
√
Hz.