HP VXI 75000 C Series, User'S And Scpi Programming Manual

Page: 369 / 438

Generating User Defined Functions 369 Appendix F
A typical use of this function would be to output an analog voltage or current
at each Scan Trigger of the HP E1415 and over the range of the haversine.
For example, suppose you wanted a new position of an analog output to
move from 1ma to 3ma over a period of 100msec. If your TRIG:TIMER
setting or your EXTernal trigger was set to 2msec, then you would want to
force 50 intervals over the range of the haversine. This can be easily done
by using a scalar variable to count the number of times the algorithm has
executed and to scale the variable value to the -PI/2 to PI/2 range. 3ma is
multiplied times the custom function result over each interval which will
yield the shape of the haversine (.003*sin(x)+.001). This is illustrated in the
example below. The program listings on the disc(and printed later in this
appendix) illustrate the actual program used to generate this haversine
function. You need only supply the algebraic expression in my_function(),
the desired range over which to evaluate the function(which determines the
table range), and the name of the function. The Build_table() routine (see
example file sine_fn.cs) creates the table for the function, and the
ALG:FUNC:DEF writes that table into HP E1415 memory. The table
MUST be built and downloaded BEFORE trying to use the function.
The following is a summary of what commands and parameters are used in
the program examples. Table 1 shows some examples of the accuracy of the
custom function with various input values compared to an evaluation of the
actual transcendental function found in ’C’ or RMB. Please note that the
Mx+B segments are located on boundaries specified by 2/64 on each side of
X=0. This means that if you select the exact input value that was used for
the beginning of each segment, you WILL get exactly the calculated value
of that function at that point. Any point between segments will be an
approximation dependent upon the linearity of that segment. Also note that
values of X = 2 and X = -2 will result in Y=infinity.
Figure 6-9. A Haversine Function