HP 8920B - Page 79

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Chapter 3, HP-IB Command Guidelines
Guidelines for Operation
Guidelines for Attribute Units
• When setting the value of measurement functions REFerence, METer, HLIMit and
LLIMit through HP-IB, a non–Attribute Unit unit-of-measure must be specified in the
command string, otherwise the current Attribute Unit is assumed by the Test Set.
For example, if the Test Set is in a RESET condition and the command
MEAS:AFR:DIST:REF:VAL 10 is sent through HP-IB, the Test Set will interpret the
data as 10 %, since % is the RESET Attribute Unit for the Distortion measurement.
Sending the command, MEAS:AFR:DIST:REF:VAL 10 DBM, would set the REFer-
ence SET value to 10 dB.
• When querying measurement functions REFerence, METer, HLIMit and LLIMit
through HP-IB, the Test Set always returns numeric values in Attribute Units, regard-
less of the current Display Units or HP-IB Units settings. Numeric values are expressed
in scientific notation.
For example, if the REF SET measurement function is displayed as 25% on the Test
Set, the value returned through HP-IB is +2.50000000E+001 (2.5×10
1
). Converting
the returned value to a format other than scientific notation must be done programmat-
ically.
• Before changing the Attribute Units for a selected measurement, the Test Set verifies
that all Data Function values can be properly converted from the current unit-of-mea-
sure to the new unit-of-measure. If it is not possible to properly convert all the values
to the new unit-of-measure, the Attribute Units are not changed and the following error
is generated: HP-IB Error: HP-IB Units cause invalid conversion
of attr.