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Creating and Running Custom Algorithms
123
Channel Input Buffer (Input Phase) BEFORE algorithms are executed
during the Calculate Phase.
•
The execution of all defined algorithms (Calculate Phase) is complete
BEFORE output values from algorithms, stored in the Channel Output
Buffer, are used to update the output channel hardware during the
Output Phase.
In other words, algorithms don’t actually read inputs at the time they
reference input channels, and they don’t send values to outputs at the time
they reference output channels. Algorithms read channel values from an
input buffer, and write (and can read) output values to/from an output buffer.
Here are example algorithm statements to describe operation:
inp_val = I108;/* inp_val is assigned a value from input buffer element 8 */
O116 = 22.3;/* output buffer element 16 assigned the value 22.3 */
O125 = O124;/* output buffer [24] is read and assigned to output buffer [25] */
A Common
Error to Avoid
Since the buffered input, algorithm execution, buffered output sequence is
probably not a method many are familiar with, a programming mistake
associated with it is easy to make. Once you see it here, you won’t do this in
your programs. The following algorithm statements will help explain:
O124.B0 = 1;/* digital output bit on HP E1533 in SCP position 3 */
O124.B0 = 0;
Traditionally you expect the first of these two statements to set output
channel 24, bit 0 to a digital 1, then after the time it takes to execute the
second statement, the bit would return to a digital 0. Because both of these
statements are executed BEFORE any values are sent to the output
hardware, only the last statement has any effect. Even if these two
statements were in separate algorithms, the last one executed would
determine the output value. In this example the bit would never change. The
same applies to analog outputs.
Algorithm
Execution Order
The buffered I/O sequence explained previously can be used to advantage.
Multiple algorithms can access the very same buffered channel input value
without having to pass the value in a parameter. Any algorithm can read and
use as its input, the value that any other algorithm has sent to the output
buffer. In order for these features to be of use you must know the order in
which your algorithms will be executed. When you define your algorithms
you give them one of 32 pre-defined algorithm names. These range from
’ALG1’ to ALG32’. Your algorithms will execute in order of its name. For
instance if you define ’ALG5’, then ’ALG2’, then ’ALG8’, and finally ’ALG1’,
when you run them they will execute in the order ’ALG1’, ’ALG2’, ’ALG5’,
and 'ALG8'. For more on input and output value sharing, see “Algorithm to
Algorithm Communication” on page 130.
Summary of Contents for VXI 75000 C Series
Page 2: ......
Page 16: ...16 ...
Page 18: ......
Page 30: ...30 Getting Started Chapter 1 Notes ...
Page 32: ...32 Field Wiring Chapter 2 Figure 2 1 Channel Numbers at SCP Positions ...
Page 44: ...44 Field Wiring Chapter 2 Figure 2 11 HP E1415 Terminal Module ...
Page 54: ...54 Field Wiring Chapter 2 Notes ...
Page 61: ...Programming the HP E1415 for PID Control 61 Chapter 3 Programming Overview Diagram ...
Page 136: ...136 Creating and Running Custom Algorithms Chapter 4 Notes ...
Page 152: ...152 Algorithm Language Reference Chapter 5 Notes ...
Page 304: ...304 HP E1415 Command Reference Chapter 6 Command Quick Reference Notes ...
Page 308: ...308 Specifications Appendix A Thermocouple Type E 200 800C SCPs HP E1501 02 03 ...
Page 309: ...Specifications 309 Appendix A Thermocouple Type E 200 800C SCPs HP E1508 09 ...
Page 310: ...310 Specifications Appendix A Thermocouple Type E 0 800C SCPs HP E1501 02 03 ...
Page 311: ...Specifications 311 Appendix A Thermocouple Type E 0 800C SCPs HP E1509 09 ...
Page 312: ...312 Specifications Appendix A Thermocouple Type E Extended SCPs HP E1501 02 03 ...
Page 313: ...Specifications 313 Appendix A Thermocouple Type E Extended SCPs HP E1508 09 ...
Page 314: ...314 Specifications Appendix A Thermocouple Type J SCPs HP E1501 02 03 ...
Page 315: ...Specifications 315 Appendix A Thermocouple Type J SCPs HP E1508 09 ...
Page 316: ...316 Specifications Appendix A Thermocouple Type K SCPs HP E1501 02 03 ...
Page 317: ...Specifications 317 Appendix A Thermocouple Type R SCPs HP E1501 02 03 ...
Page 318: ...318 Specifications Appendix A Thermocouple Type R SCPs HP E1508 09 ...
Page 319: ...Specifications 319 Appendix A Thermocouple Type S SCPs HP E1501 02 03 ...
Page 320: ...320 Specifications Appendix A Thermocouple Type S SCPs HP E1508 09 ...
Page 321: ...Specifications 321 Appendix A Thermocouple Type T SCPs HP E1501 02 03 ...
Page 322: ...322 Specifications Appendix A Thermocouple Type T SCPs HP E1508 09 ...
Page 323: ...Specifications 323 Appendix A 5K Thermistor Reference SCPs HP E1501 02 03 ...
Page 324: ...324 Specifications Appendix A 5K Thermistor Reference SCPs HP E1508 09 ...
Page 325: ...Specifications 325 Appendix A RTD Reference SCPs HP E1501 02 03 ...
Page 326: ...326 Specifications Appendix A RTD SCPs HP E1501 02 03 ...
Page 327: ...Specifications 327 Appendix A RTD SCPs HP E1508 09 ...
Page 328: ...328 Specifications Appendix A 2250 Thermistor SCPs HP E1501 02 03 ...
Page 329: ...Specifications 329 Appendix A 2250 Thermistor SCPs HP E1508 09 ...
Page 330: ...330 Specifications Appendix A 5K Thermistor SCPs HP E1501 02 03 ...
Page 331: ...Specifications 331 Appendix A 5K Thermistor SCPs HP E1508 09 ...
Page 332: ...332 Specifications Appendix A 10K Thermistor SCPs HP E1501 02 03 ...
Page 333: ...Specifications 333 Appendix A 10K Thermistor SCPs HP E1508 09 ...
Page 334: ...334 Specifications Appendix A Notes ...
Page 346: ...346 Glossary Appendix C Notes ...
Page 388: ...388 Generating User Defined Functions Appendix F Notes ...