The unstrained reference measurement is made because of the
unbalanced bridge method of strain measurement. Instead of
balancing (nulling) the bridge before each measurement, an
unstrained reference ((Vout/Vs)unstrained) is measured for each
channel. The unbalanced bridge measurement technique is described
in the next section.
3. Add tension to the specimen.
4. Configure the multimeter and make the strain measurement(s).
MEASure:STRain:
strain_function
? (@
channel_list
)
or
CONFigure:STRain
:strain_function
,(@
channel_list
)
When
MEASure
is used, the multimeter is configured and the
measurement is immediately taken. Because of this, variations to the
multimeter configuration (range, aperture time) are limited to the
values set by the
MEASure
command (see the table on
page 77
).
When
CONFigure
is used, the multimeter is configured but the
measurement is not taken until
READ?
or
INIT
is executed. Thus,
low-level multimeter commands (covered in the multimeter manual)
can be used to change the configuration (range, aperture time) before
the measurement is made.
Note
The strain measurement commands identified in this procedure are HP
E1326B/E1411B Multimeter commands. Information on how these
commands relate to strain measurements and how the multimeter makes
strain measurements is contained in this manual. Information on the entire
multimeter command set and on general multimeter operation is contained
in the HP E1326B/E1411B User’s Manual.
Unbalanced Bridge
Measurement
Technique
The strain gage multiplexers measure strain using an unbalanced
Wheatstone Bridge (see “ Understanding the Strain Gage Measurement
Circuits” on
page 53
). Unbalanced bridge measurement techniques do not
require the bridge to be balanced (manually or electronically) before strain
measurements are made.
50 Understanding the Strain Gage Multiplexers
Chapter 4
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