Acquiring Readings - Keithley 6430 Instruction Manual

WARNING
NOTE

Acquiring readings

:FETCh?
Description
NOTE
NOTE
When :CONFigure is sent, the output will turn on. Beware of hazardous
voltage that may be present on the output terminals.
This command is automatically asserted when the :MEASure? command is sent.
This query command requests the latest post-processed readings stored in
the sample buffer. See Appendix C. After sending this command and
addressing the SourceMeter to talk, the readings are sent to the computer.
This command does not affect the instrument setup.
This command does not trigger source-measure operations; it simply
requests the last available readings. Note that this command can repeatedly
return the same readings. Until there are new readings, this command con-
tinues to return the old readings. For example, assume that the
SourceMeter performed 20 source-measure operations. The :FETCh? com-
mand will request the readings for those 20 source-measure operations. If
:FETCh? is sent while performing source-measure operations (ARM annun-
ciator on), it will not be executed until the SourceMeter goes back into idle.
The readings that are acquired depend on which data elements are selected
(Section 17, FORMat subsystem, Data elements), and what the instrument is
presently programmed to source-measure. Measure readings take priority
over source readings, and functions not sourced or measured are assigned
the NAN (not a number) value of +9.91e37.
For example, assume that voltage, current and resistance readings are
selected as data elements, and the instrument is programmed to Source V
and Measure I. A reading string acquired by :FETch? will include the pro-
grammed
V-Source value and the I-Measure reading. The reading for resistance will
be NAN since resistance was not measured.
If the SourceMeter is instead programmed to Source V and Measure V, the
voltage reading will be the V-Measure reading (not the programmed
V-Source value). Both current and resistance readings will be NANs (cur-
rent is not measured or sourced).
The :FETCh? command is automatically asserted when the :READ? or :MEASure?
command is sent.
See Appendix C for a detailed explanation on how data flows through the various
operation blocks of the SourceMeter. It clarifies the types of readings that are
acquired by the various commands to read data.
SCPI Signal-Oriented Measurement Commands 16-3