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

Page: 114 / 438

114 Creating and Running Custom Algorithms Chapter 4
Describing the HP E1415 Closed Loop Controller
The HP E1415 is really a self contained data acquisition and control
platform in a single C-size VXIbus module. Once configured for operation
and started using its SCPI command set, the module is controlled by the
algorithm(s) it is executing. It is the algorithms that have exclusive access to
acquired data from input channels, and it is the algorithms that generate
values that control the analog and digital output channels. It is the
calculation and decision making capability provided by its Algorithm
Language that makes the HP E1415 a closed loop controller. By placing the
control "computer" (the algorithm) inside the data acquisition and control
instrument, the data acquisition, the control decision making, and the data
output phases are as tightly coupled as they can be. The time required for the
system to respond to changing input values is at most one execution of the
control algorithm. No data exchange to or from an external computer is
required in this cycle.
What is a Custom Algorithm?
The only thing that separates the HP E1415’s standard PID algorithms from
custom algorithms is that the standard PIDs are "built-in". That is, they are
in the HP E1415’s driver, and the driver can automatically insert your
channel references into the code as it’s loading it. Otherwise there is no
difference, in fact the standard PIDs are written in the same Algorithm
Language you will use to create your custom algorithms. The source code
for PIDA, PIDB, as well a third algorithm "PIDC" are supplied with your
HP E1415 so you can use these as the basis for custom PID algorithms.
Overview of the Algorithm Language
As mentioned in the Introduction, the HP E1415’s Algorithm Language is
based on the ANSI ’C’ programming language. This section will present a
quick look at the Algorithm Language. The complete language reference is
provided in Chapter 5.
Arithmetic Operators: add +, subtract -, multiply *, divide /
NOTE: See “Calling User Defined Functions” on page 122.
Assignment Operator:
=
Comparison Functions: less than <, less than or equal <=, greater than
>, greater than or equal >=, equal to ==, not equal to !=
Boolean Functions:
and &&, or ||, not !
Variables: scalars of type static float, and single dimensioned arrays of
type static float limited to 1024 elements.
Constants:
32-bit decimal integer; Dddd... where D and d are decimal digits but D is
not zero. No decimal point or exponent specified.
32-bit octal integer; 0oo... where 0 is a leading zero and o is an octal digit.