Recording the total of a rolling sequence

Question

I am recording times taken for a production sequence to complete. The time is recorded in seconds by the plc, which counts upward from zero until the production sequence has completed, after a short pause the plc resets itself to zero and repeats the count for the next sequence. I would like to write the totals of each sequence to a tag so I can show total production times for each sequence in a table or on a historical chart.
I am unsure how to program labVIEW to take the total times for each repetition of the sequence and write the information to say, a tag. If anyone can offer an example of how I can retrieve these values I would be u-n-b-e-l-i-e-v-a-b-l-y grateful!!
Many thanks,
Stuart

Answer 1

Hi Stuart,
"I would like labVIEW to count the cycle/recognise the end of cycle"
From your descriptions so far, the only indication that your HMI/LabVIEW DSC program will have that a production cycle is complete is/are:
1) there will be a "short pause" during which the Total Cycle Time value will stick at its maximum value; and
2) the Total Cycle Time value gets reset to zero.
Idea: Monitor the Total Cycle Time timer/counter/data register as an Input tag (not logged). Use a shift register in your state machine's ** while loop to store the value from the previous time you monitored this Total Cycle Time tag.  When the current value is < (less than) the previous value, a new cycle has started. Write the previous value to a 'Total Cycle Time' Memory tag that is configured to log.
" Also, I have not managed to configure a tag with a deadband of 0% without an error appearing in the configuration editor"
That's a headache. What kind of error message (if any) do you get? Have you tried it for different types of tags (Input, Memory, etc. etc.). What deadband(s) are you trying to set to zero?
There's a useful KnowledgeBase doc summarizing deadbands here.
If you want to have a logging deadband of 0%, you do have to have the Tag Engine Update deadband at 0% as well.
** Re: State machine
If you haven't done so already, you may want to look at examples of the use of a state machine as an overall structure for LabVIEW programs. Simple examples ship with LabVIEW. If you search this forum, you will find many discussions on its merits and different forms. There've also been a number of presentations/docs on the idea. A couple which come to mind are:
- Rob Humfeld's NI Week 2004 presentation here (the "State Machines" link at the bottom).
- LabVIEW Application Design Patterns from 2002.
Without the use of some kind of flavour of state machine, the block diagram for a LabVIEW DSC program can get messy and hard to debug very fast.
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