Trend on Panel View 800

marvis

Member
Join Date
Mar 2016
Location
Italy
Posts
108
Hello everyone,

I'm using the trend of a PanelView800 to record data in a USB memory but I have a problem: the data, not always, but very often, read several times the same data.
Where am I wrong?

Thank you in advance.

Immagine1.png Immagine2.png Immagine4.png
 
The logging seems to occur when [GUN 02 ENABLE DATA // B3:12/5] is 1.

[GUN 02 ENABLE DATA // B3:12/5] is latched, to 1 on a rising edge of [Start Trend GUN#02 // B3:13/0].

The rising edge of [GUN 02 ENABLE DATA // B3:12/5] triggers the copying of data, ONCE (rising edge) to F8:6 and N11:49. The is the key to the answer to your question.



[GUN 02 ENABLE DATA // B3:12/5] becoming 1 also starts a 1500ms = 1.5s timer; at the expiry of that timer, [GUN 02 ENABLE DATA // B:12/5] is unlatched, to 0, which I assume will stop the logging.


It appears the logging occurs once per second: the two rows in the output file with the same value, 980, have different time stamps. Since those two rows occur one seconds apart, it is possible that they could occur during one 1.5s cycle of the timer.


E.g. say

  • The start of logging is triggered at time-of-day 10:27:40,600 of the PV800.
    • The current values are copied to F8:6 and N11:49, but only ONCE.
    • The timer starts its 1500s timing
    • B3:12/5 is latched to 1
  • At the start of the next whole second, 10:26:41,000
    • The timer .ACC value is 400, so it has not expired
    • B3:12/5 is 1
      • which triggers the PV800 to the values from F8:6 and N11:40
  • At the start of the second whole second, 10:27:42,000
    • the timer .ACC value is 1400, so the timer has not expired
    • B3:12/5 is still 1
      • which again triggers the PV800 to log the values from F8:6 and N11:40 a second time
        • And those values have not changed
  • At 10:27:42,100
    • the timer .ACC value reaches 1500,
      • so the timer expires and .DN becomes 1,
        • so B3:12/5 is unlatched to 0
          • Which stops the logging
 
Thank you so much for your reply and your observation.
You have been very clear.

In your opinion, what solution can I take to prevent this type of problem from occurring?
 
Thank you so much for your reply and your observation.
You have been very clear.

In your opinion, what solution can I take to prevent this type of problem from occurring?


The right solution would be for the PV to flag the PLC when it takes the first samples. I don't know enough about PVs to know how to do that.


I wonder if you could set the PV [Timespan] parameter to 0.5s, i.e. less than the 1s PV [Sample Interval], and that might stop the PV from trying to take the second sample. If the PV [Timespan] needs to be a whole number (integer), then change it to 1s and set the PV [Sample Interval] parameter to 2s.


Even if you do not change the PV [Timespan], but change the PV [Sample Interval] to 2s or 3s, then the PLC 1.5s (1500ms) timer will have expired, and the Log Trigger Tag (LogData_Gun02) will be 0, when the PV is scheduled to take the second sample, so the second sample will not be taken.



Using timers to make things happen is not usually the best approach, but sometimes it is easier than doing it right.
 
Thank you very much for support.

So I will try with Timespan 20 seconds (I don't touch this parameter) and Sample Interval with 3 seconds. Is it right?

Thanks.
 

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