Relay Strain Gage Measurements with an External Voltmeter
This program shows how strain measurements are made using a relay strain
gage multiplexer switchbox and an external (HP 3458A) voltmeter.
!Dimension computer variables to store the readings.
DIM Vout_unstr(1:3),Vout_str(1:3),Vr(1:3),Epsilon(1:3)
!Clear and reset the external multimeter.
CLEAR 722
OUTPUT 722;"RESET"
!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), and so that it outputs a trigger signal when the
!measurement is complete (to trigger the multiplexer).
OUTPUT 722;"PRESET NORM"
OUTPUT 722;" MEM FIFO"
OUTPUT 722;" TBUFF ON"
OUTPUT 722;" TRIG EXT"
OUTPUT 722;" EXTOUT RCOMP,NEG"
!Configure the relay multiplexer switchbox so that it outputs a trigger signal
!(via the mainframe “Trig Out” port) when a channel is closed, and so that it is
!externally triggered (via the mainframe “Event In” port) to close a channel.
!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 EXT"
OUTPUT 70914;"SCAN:PORT ABUS"
!Download the scan list to measure Vout and Vs unstrained. Close the first
!channel in the list to start the scan.
OUTPUT 70914;"SCAN (@100:102,115)"
OUTPUT 70914;"INIT"
DISP
"Add tension to the specimen; then press ’Continue’"
PAUSE
DISP ""
!Download the scan list to measure Vout and Vs strained. Close the first
!channel in the list to start the scan.
OUTPUT 70914;"SCAN (@100:102,115)"
OUTPUT 70914;"INIT"
!Compute and display the 1/4 bridge strain measurements.
ENTER 722;Vout_unstr(*),Vs_unstr,Vout_str(*),Vs_str
CALL Strn_cmput(Vr(*),Vout_str(*),Vout_unstr(*),Vs_str,Vs_unstr)
END
SUB Strn_cmput(Vr(*),Vout_str(*),Vout_unstr(*),Vs_str,Vs_unstr)
FOR I=1 TO 3
Vr(I)=Vout_str(I)/Vs_str-Vout_unstr(I)/Vs_unstr
Epsilon(I)=-4*Vr(I)/2.11E-6*(1+2*Vr(I))
PRINT Epsilon(I)
NEXT I
SUBEND
Chapter 3
Making Strain Gage Measurements 41
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