Remote Programming - Buffer; Buffer Commands - Keithley 2701 User Manual

6-8 Buffer
Standard deviation
This mode displays the standard deviation of buffered readings. The following equation is
used to calculate standard deviation:
where:
NOTE
Remote programming — buffer
NOTE
NOTE

Buffer commands

NOTE
The commands to perform buffer operations are listed in Table 6-1. Details on these
commands follow the table.
NOTE
y =
y is the standard deviation.
X is a stored reading.
i
n is the number of stored readings.
If the standard deviation calculation is being performed on a buffer that has
more than 1000 readings, the "CALCULATING" message will flash to indicate
that the Model 2701 is busy. While busy with the calculation, front panel keys
will not operate. It will take approximately five seconds to calculate standard
deviation on 450,000 readings.
When readings are stored in the buffer by the TRACe command (or by front
panel data store operation), INIT and multi-sample READ? queries are locked
out. With readings in the buffer that were stored in that manner, you cannot use
the INIT or READ? command if sample count is >1 (error -225, out of memory).
The measurement event register can be read to check when the buffer becomes
¼, ½, ¾, or full. Status registers are covered in Section 11. "Example 3 – Read
BHF bit of measurement event register" shows how to read the BHF (buffer half
full) bit of the measurement event register.
When measurements are performed, the readings are fed to other enabled
operations, including the Buffer. Appendix D explains "Data flow (remote
operation)," page D-7, and the commands used to read the buffer and buffer
statistics.
Optional command words and most queries are not included in Table 6-1. The
unabridged tables for all SCPI commands are provided in Section 15.
2
n n
⎛ ⎛ ⎞
⎜ ⎜ ⎟
∑ ∑
2
1
-- -
X – X
⎜ ⎜ ⎟
i i
n
⎝ ⎝ ⎠
i = n 1 – i = 1
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n 1 –
Model 2701 User's Manual
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