Measurement Commands
FETCh[1]|2|3|4 Queries
EPM-P Series Power Meters Programming Guide
2-23
FETCh[1]|2|3|4 Queries
The
FETCh?
queries set the specified window’s measurement function to
either single channel, difference or ratio measurements with relative
mode either off or on. They then recalculate the measurement and place
the result on the bus. The format of the result is set by
FORM[:READ][:DATA]
. Refer to chapter 6, Format, for further
information.
The query returns a measurement result whenever it is valid. The
measurement result becomes invalid under the following conditions:
•
When
*RST
is executed.
•
Whenever a measurement is initiated.
•
When any
SENSe
parameter, such as frequency, is changed.
If data is invalid, the
FETCh?
query is not completed until all data is valid.
The exceptions to this are, if the power meter is in the idle state and the
data is invalid, or the power meter has been reconfigured as defined above
and no new measurement has been initiated. In such cases, the
FETCh?
routine generates the error -230, “Data corrupt or stale” and no result is
returned. A common cause for this error is receiving a
FETCh?
after a
*RST
. If the expected value and resolution parameters are not the same as
those that were used to collect the data, error -221, “Settings conflict”
occurs.
Note
When
TRIG:SOUR
is
INT1
,
INT2
or
EXT
and a new acquisition has
been initiated (using the
INIT
command for example),
FETCH?
waits until the trigger takes place before executing. If trigger
conditions are not satisfied—when the trigger level differs greatly
from the signal level for example—this can give the impression
that the power meter has hung.
To ‘unlock’ the power meter and adjust trigger settings, a GPIB
bus execute clear must be performed.
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