Specifications

• The FET multiplexer switchbox can be used with an external
voltmeter without using the digital bus cable. Connect the voltmeter
to the switchbox as indicated in Figure 2-7 on page 31. However, do
not connect the cable between the voltmeter’s "voltmeter
complete" port and the mainframe’s "Event In" port. Modify
the previous program as follows:
!Configure the external multimeter for DC voltage measurements. Configure its
!trigger system such that the multimeter is externally triggered (when the
!multiplexer channel is closed).
OUTPUT 722;"PRESET NORM"
OUTPUT 722;" MEM FIFO"
OUTPUT 722;" TBUFF ON"
OUTPUT 722;" TRIG EXT"
!Configure the FET multiplexer switchbox so that it outputs a trigger pulse
!when a channel is closed. Set the switchbox to be triggered by the *TRG
!command. Close the multiplexer tree relays necessary to make DC voltage
!measurements. Connect the analog bus, which carries the bridge output and
!excitation voltages, to the HI, LO, and Guard terminals on the multiplexer
!terminal module.
OUTPUT 70914;"*RST"
OUTPUT 70914;"OUTP ON"
OUTPUT 70914;"TRIG:SOUR:BUS"
OUTPUT 70914;"SCAN:MODE VOLT"
OUTPUT 70914;"SCAN:PORT ABUS"
!Measure Vout and Vs unstrained. INIT closes the first channel in the list.
!(*TRG) is used to advance and complete the scan. The WAIT statements allow
!the voltmeter measurement to complete before the next channel is closed.
OUTPUT 70914;"SCAN (@100:102,115)"
OUTPUT 70914;"INIT"
WAIT .1
FOR I=1 TO 4
OUTPUT 70914;"*TRG"
WAIT .1
NEXT I
DISP "Add tension to the specimen; then press ’Continue’"
PAUSE
DISP ""
!Measure Vout and Vs strained. Again, INIT closes the first channel in the list.
!Backplane triggers (*TRG) are issued to advance and complete the scan. The
!WAIT statements allow the voltmeter measurement to complete before the next
!channel is closed.
OUTPUT 70914;"SCAN (@100:102,115)"
OUTPUT 70914;"INIT"
WAIT .1
FOR I=1 TO 4
OUTPUT 70914;"*TRG"
WAIT .1
NEXT I
This modification allows the multimeter to be triggered when a multiplexer
channel is closed. However, the multiplexer is triggered by the user (
*TRG)
which advances the scan.
Chapter 3 Making Strain Gage Measurements 45
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