VXI VT1422A - Manual (Page 88)

86 Programming the VT1422A & VT1529A/B for Remote Strain Measurement Chapter 3
/* set up the sample timer. This controls the channel to channel scan
rate and can be important when channels need more than the default
40 microsecond sample time. */
errStatus=hpe1422_cmd(sessn,"sample:timer 40E-6"); /* *RST default */
/* INITiate the trigger system to execute a measurement scan */
errStatus=hpe1422_cmd(sessn,"INIT:IMMediate");
/* retrieve readings from FIFO. Notice that for each scan, we read the
number of values in the FIFO (sens:data:fifo:count?), then apply
that value to control the number of readings we read with the
hpe1422_readFifo_Q() function. For continuous data acquisition, see
Chapter 4 of the manual under "Reading Fifo Data." */
errStatus=hpe1422_cmd(sessn,"INIT:IMMediate");
/* find the number of readings present in the FIFO */
errStatus=hpe1422_cmdInt32_Q(sessn,"sense:data:fifo:count?",&result32);
/* read the values from the FIFO. count returns number actually read */
errStatus=hpe1422_readFifo_Q(sessn, result32, 512, brdg_array, &count);
Measure Bridge Voltages
and Convert to Strain
If this method is desired, voltage measurements will be made at the strain
bridges while unstrained, then again while under strain. The excitation
voltage will also be measured at each bridge. Using this data as well as the
gage factor, strain conversion equations can be calculated in the computer.
1. Set the measurement function to voltage with the
[SENSe:]FUNC:VOLT <range>,(@<ch_list>) command.
2. The type of bridge connection must be specified using the
[SENSe:]STRain:BRIDge[:TYPE] <select>,(@<ch_list>)
command. The allowable values for <select> are: FBEN, HBEN,
Q120 (quarter bridge, 120
Ω), Q350 (quarter bridge, 350 Ω) or USER
(quarter bridge, with the user supplied resistor).
The power-on and *RST default setting is FBEN.
3. Configure channels to measure their strain bridge outputs rather
than their excitation supply. This is done by sending the
[SENSe:]STRain:CONNect BRIDge,(@<ch_list>) command.
The power on and reset setting is BRIDge.
4. Use the MEAS:STR:UNSTrained? (@<ch_list>) query to read the
voltage on each specified channels while the bridges are unstrained.
This command which will take an average of 32 voltage readings on
each channel and save the values to the FIFO buffer. The command
returns the number of readings in the FIFO. When using this method,
loaded algorithms are not executed to avoid putting extraneous
readings into the FIFO buffer.
5. Use the MEAS:STR:EXCitation? (@<ch_list>) query to sense the
excitation at each of the specified bridges. This command will take an
average of 32 voltage readings on each channel and save the values to
the FIFO buffer. The command returns the number of values in the
FIFO. When using this method, loaded algorithm(s) are not executed
to avoid putting extraneous values into the FIFO buffer.