Optimize vi response to tag changes

Question

what is the best way(fastest response time) to get tag values into a vi?? I made a vi with three loops monitoring boolean transitions. One loop used a front panel indicator with HMI wizard and local variable. This loop had a timer set for 25ms. Another loop used a read tag with constant input of .025. The third loop used the trend tags vi with .025 time constant. I then used the get timestamp vi to read when the transitions occur. The read tag loop was usually the fastest to notice transitions of the boolean value. Sometimes it was 50ms faster, average was around 17ms faster for read tag loop. When the tag turns off, I need to read 500 analog tags in less than .75 seconds. Data is coming into the tag engine through an OPC s
erver and plc over ethernet. Is the tag engine designed for this fast of response time??
Attachments:
speed_test.vi ‏144 KB
analyze_speed_test_results.vi ‏45 KB

Answer 1

Hi,
The most efficient way to write to the tag engine is using the Write tag.vi. However you have to have in mind that the LabVIEW DSC code is not the only part responsible for the communication between your PC and the PLC, the speed at which the OPC Server communicates to the PLC is crucial to accomplish your goals, so make sure that your phisical connection is able to handle the poll rate defined in the OPC server.
Also, performance is something very particular to each system, it will depend on the speed of your processor, how much memory you have available as well as how fast is the connection between the PLC and the PC, so there is only one way to find out if you can achieve what you want in your particular system, trying to implement it.
Andre O
liveira