VXI VT1419A Multifunction Plus, Руководство пользователя

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Note the “TRIG:TIMER 0.01" command will establish the scan trigger rate at
which measurements are taken and C algorithms are executed. This rate was chosen
purposely to illustrate the concept of slowing down data acquisition at multiples of
10 ms. Also note that the data format of ”FORM REAL,32" is used so the
maximum rate can be achieved when reading data from the FIFO.
The second object, Download Algorithm, illustrates how to download a C program
to access the channel variables for input measurements. This object consists of a
REPEAT loop with a count range to automatically generate 32 of the
“writefifo(Ixx);” statements. The Ixx will range from I100-I131, which represents
each of the first 32 analog input channels. The only function this algorithm will
have is to read all 32 analog input values for each scan trigger and place that data
into the FIFO.
The Output and Input Data File text boxes allow names of data files to be specified.
The Output Data File assumes the working directory unless the entire path is
specified. This file will be cleared upon executing the “RUN” key of Agilent VEE.
If the LOG ON switch is set, all data acquired will be written to the specified data
file. If the VT1419A switch is selected, then data is acquired from the actual input
channels. If FILE is selected, data is read from the specified Input Data File as
though it were coming from the input channels. The assumption is that this data file
was created with this example using the LOG ON mode or created with the logging
function of the example
panl1419.vee . Note that both the LOG ON/OFF and the
FILE/E1419 switches come BEFORE the REPEAT loop. Therefore, these
parameters cannot be modified AFTER executing the “RUN.”
The REPEAT provides the rate at which Agilent VEE can perform the following
actions:
·
Reads the desired algorithm execution rate for storing data into the FIFO.
·
Reads the desired channels to display on the strip chart.
·
Reads 10-scans (320 values) of data from the FIFO.
·
Writes 10 readings for each selected channel to the strip chart.
·
Reads the desired SCP channels to display a Current Value Table (CVT) of
data returned and displays that data.
The more operations placed in this loop, the more time will placed between
accesses to the FIFO. The execution speed of Agilent VEE is dependent upon the
speed of the computer, how many I/O operations it is performing, and whether or
not the Compiled mode of Agilent VEE 4.0 is being used. If running a
Pentium-class PC, the REPEAT loop will easily keep up with the acquisition rate of
the VT1419A card and provide very near real-time data on the strip chart. Slower
computers may fall behind. The TRIG:TIMER interval can be altered to slow down
the acquisition rate or move the slider control to slow down the rate of placing data
into the FIFO.
Note that one can select which SCP data will to be monitored on the alphanumeric
display. Each SCP can have up to eight channels of analog input, so selecting SCP
0-3 will allow for all eight channels to be displayed. The data displayed is just one
of the ten readings acquired from the 320 FIFO readings. Normally, the better
choice is to use the VT1419A’s CVT and read that directly; however, since the data
was already read, adding the additional I/O statement to fetch the eight channels
from the CVT is an unnecessary performance slow-down for this application.
VEE Programming Examples
Simple Data Logger Example
164 Chapter 5
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