Keithley 2790, Reference Manual

Page: 199 / 568

6-8 Model 2790 SourceMeter
®
Switch System Reference manual
Standard deviation
This mode displays the standard deviation of buffered readings. The following equation is
used to calculate standard deviation:
where: y is the standard deviation.
X
i
is a stored reading.
n is the number of stored readings.
klqb
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 2790 is busy. While busy with the calculation, front panel keys
will not operate.
Remote programming — buffer
klqb
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).
klqb
The measurement event register can be read to check when the buffer becomes ,
,
i
, or full. Status registers are covered in Section 11 .
Buffer commands
klqb
When measurements are performed, the readings are fed to other enabled oper-
ations, including the Buffer. Appendix C explains data flow and the commands
used to read the buffer and buffer statistics.
The commands to perform buffer operations are listed in Table 6-1 . Details on these com-
mands follow the table.
klqb
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 .
y
X
i
2
i n 1 – =
n
∑
1
n
---
X
i
i 1 =
n
∑
⎝ ⎠
⎜ ⎟
⎜ ⎟
⎛ ⎞
2
⎝ ⎠
⎜ ⎟
⎜ ⎟
⎛ ⎞
–
n 1 –
--------------------------------------------------------------- =