100 Programming the VT1422A for Data Acquisition and Control
Chapter 4
Detailed Instrument
Operation Cycle
Figure 4-2 illustrates the timing of all these operations and describes the
VT1422A's input-update-execute algorithms-output phases. This
cycle-based design is desirable because it results in deterministic operation
of the VT1422A. That is, the input channels are always scanned and the
output channels are always written at pre-defined intervals. Note, too, that
any number of input channels or output channels are accessible by any of up
to 32 user-written algorithms. The algorithms are named ALG1-ALG32 and
execute in numerical order.
In Phase 1, all input channels specified in the ROUTe:SEQuence:DEFine
command and/or referenced in downloaded algorithms are scanned.
Phase 1A is for Runtime Remote Scan Verification and is optional. When one
or more special scan status variables (S1xx) are included in an algorithm,
this time is required to evaluate the scan status of each VT1539A SCP
channel reference by a status variable. The time required is 230
µ
s + 40
µ
s
* (number of S1xx variables referenced). If no status variables are
referenced in any algorithms, then Phase 1A is not executed.
Notice the Update Window (Phase 2) illustrated in Figure 4-2. This window
has a user-specified length and is used to accept and make changes to local
and global variables from the supervisory computer. Up to 512 scalar or
array changes can be made while executing algorithms. Special care was
taken to make sure all changes take place at the same time so that any
particular algorithm or group of algorithms all operate on the new changes
at a user-specified time. This does not mean that all scalar and array changes
have to be received during one cycle to become effective at the next cycle.
On the contrary, it may take several cycles to download new values,
especially when trying to re-write 1024 element arrays and especially when
the trigger cycle time is very short.
There are multiple times between the base triggers where scalar and array
changes can be accepted from the supervisory computer and these changes
are kept in a holding buffer until the supervisory computer instructs the
changes to take effect. These changes then take place during the Update
window and take effect BEFORE algorithms start executing. The
"do-update-now" signal can be sent by command (ALG:UPD) or by a
change in a digital input state (ALG:UPD:CHAN). In either case, the
programmer has control over when the new changes take effect.
The VT1422A's ability to execute programs directly on the card and its fast
execution speed give the programmer real-time response to changing
conditions. Plus, programming the card has been made very easy to
understand. The C language was chosen for writing user programs as this
language is already considered the industry standard. Choosing C allows the
user to write algorithms on PCs or UNIX workstations that have
C compilers, so they can debug algorithms before execution on the card. The
VT1422A also provides good debugging tools that permit users to determine
worst-case execution speed, monitor variables while running, and
selectively enabling/disabling any of the VT1422A's 32 algorithms.
Summary of Contents for VT1422A
Page 2: ...This page is blank...
Page 8: ...8 Notes...
Page 22: ...22 Support...
Page 57: ...Field Wiring 57 Chapter 2...
Page 58: ...58 Field Wiring Chapter 2...
Page 96: ...94 Programming the VT1422A VT1529A B for Remote Strain Measurement Chapter 3...
Page 162: ...160 Programming the VT1422A for Data Acquisition and Control Chapter 4...
Page 224: ...222 Creating and Running Algorithms Chapter 6...
Page 419: ...VT1422A Command Reference 417 Chapter 7 Notes...
Page 420: ...418 VT1422A Command Reference Chapter 7 Notes...
Page 425: ...Specifications 423 Appendix A Thermocouple Type E 200 800 C SCPs VT1501 02 03A...
Page 426: ...424 Specifications Appendix A Thermocouple Type E 200 800 C SCPs VT1508 09A...
Page 427: ...Specifications 425 Appendix A Thermocouple Type E 0 800 C SCPs VT1501A 02A 03A...
Page 428: ...426 Specifications Appendix A Thermocouple Type E 0 800 C SCPs VT1508A 09A...
Page 429: ...Specifications 427 Appendix A Thermocouple Type E Extended SCPs VT1501A 02A 03A...
Page 430: ...428 Specifications Appendix A Thermocouple Type E Extended SCPs VT1508A 09A...
Page 431: ...Specifications 429 Appendix A Thermocouple Type J SCPs VT1501A 02A 03A...
Page 432: ...430 Specifications Appendix A Thermocouple Type J SCPs VT1508A 09A...
Page 433: ...Specifications 431 Appendix A Thermocouple Type K SCPs VT1501A 02A 03A...
Page 434: ...432 Specifications Appendix A Thermocouple Type R SCPs VT1501A 02A 03A...
Page 435: ...Specifications 433 Appendix A Thermocouple Type R SCPs VT1508A 09A...
Page 436: ...434 Specifications Appendix A Thermocouple Type S SCPs VT1501A 02A 03A...
Page 437: ...Specifications 435 Appendix A Thermocouple Type S SCPs VT1508A 09A...
Page 438: ...436 Specifications Appendix A Thermocouple Type T SCPs VT1501A 02A 03A...
Page 439: ...Specifications 437 Appendix A Thermocouple Type T SCPs VT1508A 09A...
Page 440: ...438 Specifications Appendix A 5k Thermistor Reference SCPs VT1501A 02A 03A...
Page 441: ...Specifications 439 Appendix A 5k Thermistor Reference SCPs VT1508A 09A...
Page 442: ...440 Specifications Appendix A RTD Reference SCPs VT1501A 02A 03A...
Page 443: ...Specifications 441 Appendix A RTD SCPs VT1501A 02A 03A...
Page 444: ...442 Specifications Appendix A RTD SCPs VT1508A 09A...
Page 445: ...Specifications 443 Appendix A 2250 Thermistor SCPs VT1501A 02A 03A...
Page 446: ...444 Specifications Appendix A 2250 Thermistor SCPs VT1508A 09A...
Page 447: ...Specifications 445 Appendix A 5k Thermistor SCPs VT1501A 02A 03A...
Page 448: ...446 Specifications Appendix A 5k Thermistor SCPs VT1508A 09A...
Page 449: ...Specifications 447 Appendix A 10k Thermistor SCPs VT1501A 02A 03A...
Page 450: ...448 Specifications Appendix A 10k Thermistor SCPs VT1508A 09A...
Page 454: ...452 Specifications Appendix A...
Page 480: ...478 VT1529A B Verification Calibration Appendix C...
Page 484: ...482 Glossary Appendix D Notes...