Data Storage - Stanford Research Systems SR844 User Manual

4-22 Data Storage

Data Storage
Introduction
The SR844 can store up to 16383 points from both the Channel 1 and Channel 2 displays
in an internal data buffer. The data buffer is not retained when the power is turned off.
The data buffer is accessible only via the remote interfaces.
Configure the displays to show the desired quantity (with appropriate ratio, offset and
expand). The data buffer stores the quantities which are displayed. Only quantities which
are displayed on the CH1 or CH2 displays can be stored. Frequency, for example, cannot
be stored.
Data Points and Bins
Data points stored in the buffer are sometimes referred to by their bin position within the
buffer. The oldest data point is bin 0, the next is bin 1, etc. A buffer with N points is
numbered from 0 to N–1.
Sample Rate
The sample rate can be varied from 512 Hz down to 62.5 mHz (one point every 16
seconds). The sample rate sets how often points are added to the storage buffer. Both
displays are sampled at the same rate and at the same times.
In addition to the internal sample rates, sampling can be triggered by a remote TRIG
command or by the rear panel TTL trigger input. In this mode, one sample is taken within
2 ms of receipt of each trigger. Triggers occurring at a rate faster than 512 Hz will be
ignored.
Storage Time
The buffer holds 16383 samples taken at the sample rate. The entire storage time is
16383 divided by the sample rate.
End of Scan
When the buffer becomes full, data storage can either stop or continue.
The first case is called one–shot (data points are stored for a single buffer length). At the
end of the buffer, data storage stops and an audible alarm sounds.
The second case is called loop. In this case, data storage continues at the end of the
buffer. The data buffer will store 16383 points and start storing at the beginning again.
The most recent 16383 points will be contained in the buffer. Once the buffer has looped
around, the oldest point (at any time) is bin 0 and the most recent point is bin 16382.
The default mode is loop.
SR844 RF Lock-In Amplifier