Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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Capture Buffer 2-33
SR785 Dynamic Signal Analyzer
Capture Buffer
Input Capture samples the analog inputs at a selected sample rate and stores the samples
in memory. Storage is continuous and real-time without interruption in the data stream.
Triggering only starts the capture, it does not synchronize individual time records.
Captured data can be used as the input for all measurement groups except Swept Sine.
The capture buffer can neither be filled nor measured while in the Swept Sine
Measurement Group.
Use the [Capture] <Memory Allocation> menu to allocate memory between the capture
buffer, waterfall storage and the arbitrary source waveform. Capture memory must be
allocated before the capture buffer may be used.
Input Sampling
The input data is always digitized at the maximum sample rate. The maximum sampling
rate is 262.1 kHz when the FFT Base Frequency is 102.4 kHz and 256 kHz when the
FFT Base Frequency is 100.0 kHz OR the Measurement Group is Octave. When
capturing data in the FFT Measurement Group, it is important to choose the 100.0 kHz
Base Frequency if the captured data will be played back in the Octave Group. Only data
captured in the Order Measurement Group can be played back in the Order Measurement
group because the capture buffer contains special tachometer data in that group that is
not present in the other measurement groups.
After the inputs are digitized, they may be filtered and downsampled before being stored
in the capture buffer. This allows longer capture times at lower sampling rates. The
capture data represents a frequency span from 0 Hz to the sampling rate/2.56. All
captured data is baseband. Capturing at less than the maximum sampling rate restricts the
playback measurement span to sampling rate/2.56.
In the order measurement group, the sampling rate is determined by the user selected
maximum order and maximum rpm.
The Capture Length is selected in 2 kPoint (2048) increments limited by the user
memory allocation. A single input or both inputs may be captured. The maximum
capture length for a single input is twice the length for both inputs at a given memory
allocation.
Capture Fill
To start capture, press the [Start Capture] key. If the Trigger Mode is Auto Arm and the
Trigger Souce is Continuous, capture starts immediately. Otherwise, the selected Trigger
will be in effect and the next trigger event will start capture. The Capture Progress
indicator shows how much of the desired capture length has been filled. If the Capture
Mode is 1-Shot, capture stops when the buffer is full. Press [Stop Capture] to halt
capture before the buffer is full.
If the Capture Mode is Continuous, once capture is started, it continues indefinitely and
fills the capture buffer in a circular fashion. In this case, press [Stop Capture] to halt