Keithley 2657A User Manual

Section 3: Functions and features Model 2657A High Power System SourceMeter® Instrument Reference Manual
3-14 2657A-901-01 Rev. B/December 2012
Statistic attributes
Use the smua.buffer.getstats() function to access the reading buffer data statistics. The table
below displays the attributes that you can use to access the reading buffer statistics.
The returned parameter has the attributes described in the following table.
Attributes for accessing reading buffer data
Attribute When returned Description
n
Always The number of data points on which the statistics are based.
mean When n > 0
The average of all readings added to the buffer.
stddev When n > 1
The standard deviation of all readings (samples) added to the buffer.
min When n > 0
A table containing data about the minimum reading value added to the
buffer.
max When n > 0
A table containing data about the maximum reading value added to the
buffer.
If n equals zero (0), all other attributes will be nil because there is no data to base any statistics on.
If n equals 1, the stddev attribute will be nil because the standard deviation of a sample size of 1 is
undefined.
The min and max entries each have the attributes described in the following table.
Min and max entry attributes
Attribute Description
measurefunction
String indicating the function measured for the reading (current, voltage,
ohms or watts).
measurerange
The full-scale range value for the measure range used when the
measurement was made.
reading
The reading value.
sourcefunction
String indicating the source function at the time of the measurement
(current or voltage).
sourceoutputstate
String indicating the state of the source (off or on).
sourcerange
Full-scale range value for the source range used when the
measurement was made.
sourcevalue If bufferVar.collectsourcevalues is enabled, the sourced value
in effect at the time of the reading.
status
Status value for the reading; the status value is a floating-point number
that encodes the status value into a floating-point value.
timestamp If bufferVar.collecttimestamps is enabled, the timestamp, in
seconds, between when the reading was acquired and when the first
reading in the buffer was acquired; adding this value to the base
timestamp will give the actual time the measurement was acquired.
bufferVar is the name of the buffer. See smuX.buffer.getstats() (on page 7-177) for additional information.
Example:
The following programming example illustrates how to output mean and standard deviation statistics
from buffer 1:
statistics = smua.buffer.getstats(smua.nvbuffer1)
print(statistics.mean, statistics.stddev)

Keithley 2657A Specifications

General

Brand	Keithley
Model	2657A
Category	Measuring Instruments
Language	English