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

Page: 134 / 438

134 Creating and Running Custom Algorithms Chapter 4
writecvt( I102, 332); /* write analog value to CVT */
Exceeded = Ex ( ( I102 > Max_chan2 ) || ( I102 < Min_chan2 ) );
writecvt( I103, 333); /* write analog value to CVT */
Exceeded = Ex ( ( I103 > Max_chan3 ) || ( I103 < Min_chan3 ) );
writecvt( I116, 334); /* write 8-bit value to CVT */
Exceeded = Ex ( I116 != Mask_chan16); /* limit test digital */
If ( Exceeded ) interrupt( );
Implementing Setpoint Profiles
A setpoint profile is a sequence of setpoints you wish to input to a control
algorithm. A normal setpoint is either static or modified by operator input
to some desired value where it will then become static again. A setpoint
profile is used when you want to cycle a device under test through some
operating range, and the setpoint remains for some period of time before
changing. The automotive industry uses setpoint profiles to test their engines
and drive trains. That is, each new setpoint is a simulation of an operator
sequence that might normally be encountered.
A setpoint profile can either be calculated for each interval or pre-calculated
and placed into an array. If calculated, the algorithm is given a starting
setpoint and an ending setpoint. A function based upon time then calculates
each new desired setpoint until traversing the range to the end point. Some
might refer to this technique as setpoint ramping.
Most setpoint profiles are usually pre-calculated by the application program
and downloaded into the instrument performing the sequencing. In that case,
an array affords the best alternative for several reasons:
•
Arrays can hold up to 1024 points.
•
Arrays can be downloaded quickly while the algorithm is running.
•
Time intervals can be tied to trigger events and each N trigger events
can simply access the next element in the array.
•
Real-time calculations of setpoint profiles by the algorithm itself
complicates the algorithm.
•
The application program has better control over time spacing and the
complexity and range of the data. For example; succesive points in the
array could be the same value just to keep the setpoint at that position
for extra time periods.
The following is an example program that sequences data from an array to
an Analog Output. There are some unique features illustrated here that you
can use:
•
The application program can download new profiles while the
application program is running. The algorithm will continue to
sequence through the array until it reaches the end of the array. At
which time, it will set its index back to 0 and toggle a Digital Output
bit to create an update channel condition on a Digital Input. Then at
the next trigger event, the new array values will take effect before the
algorithm executes. As long as the new array is download into
memory before the index reaches 1023, the switch to the new array