Set up the DAQ assistant to measure
voltage.
Select the appropriate module and channel.
This will depend on which wire you use to
connect your instrument into the computer.
The modules are ordered from left to right
(mod 1, mod 2, mod 3) and the channels are
ordered from top to bottom (channel 0,
channel 1, etc.)
Choose an appropriate range of input
voltages. Select an appropriate sampling
rate and number of samples. Your
instrument can be tested from this window.
Set up the Wheatstone Bridge out of the strain
gauges on the aluminum bar. Diagram for
various bridge configurations can be found on
page 441 of the textbook. The bending
arrangement that uses only two strain gauges
can be used, but another arrangement that uses
four strain gauges is more accurate. If you
analyze the diagram carefully you will notice
that compensation is provided for both
temperature and axial force.
Clamp the end of the bar to the desk. Your bridge can be tested from the DAQ Assist window.
The arrangement to the right is one way that
the block diagram can be set up, although there
are many other arrangements that will do the
same thing. Notice that the data from the DAQ
assistant will be sent to a measurement file and
a graph.
The multiplication, addition, and numeric
constants can be added to the block diagram by
right clicking, selecting the Numeric toolbox,
and selecting the desired block. The
multiplication and addition symbols will be used
later to calibrate the system. For now, just let
the data pass through unaltered by multiplying
by 1 and adding 0.
Calibrate the instrument by hanging weights on the end of the bar. Take advantage of MS Excels linear
regression capabilities to quickly find the relationship between the voltage measured and the force on
the end of the bar.
Based on the results from MS excel, change the values in the numeric constants on the block diagram so
that graph will show the force applied on the bar. The instrument is now calibrated and can be used to
measure force.