Real Time Clock From HMI

dternosky

Member
Join Date
Feb 2016
Location
North Canton, Ohio
Posts
19
Good morning All,

I have an interesting situation that is happening in a program. They are using a RTC from the HMI to execute a move when the hours are equal to 23 (11PM) and the minutes are equal to 58. with a ONS but what is happening is that it ends up moving it twice because the minutes are rolling back by a count of 5 every 30 seconds or so. so it will go true at 58 then roll back to 53 for 30 seconds then go to 59 and roll back to 52 and so on. when it gets to 3 and then rolls back to 58 the rung goes true again and performs the move another time.

The time on the HMI itself stays true with no dropping back in the minutes. i have not seen this before and i was hoping someone has and can help me diagnose the issue. For the time being i build a 24 hour clock with a timer and counters to make the program function as desired but id rather use the clock.


Thanks,
Dave

HMI RTC.jpg
 
I have no idea why the time is jumping around.

To get around the issue and still use the clock, you could latch when the event first happens, then later unlatch.

For example, latch at 23:58, unlatch at 4:55.
 
Dave:
Why are you using RTC from hmi and not from PLC ?
Have you check how N10:0 and N10:1 are being used, are you sure they are not used or modified somewhere else ??
 
One thing to keep in mind working with ANY value coming from the HMI to PLC is that the communication is not precise. Basically, what you are doing here can and will have unpredictable result depends on Com server timing and rounding of numbers.

If you do not have a good RTC in the PLC you are using, one way around it is to keep your logic at least 2 minutes apart.
 
To have it only happen once, when the OneShot trips start a TOF timer for 9999 seconds, and if the timer/DN is on don't allow the process to repeat.
 
Dave:
Why are you using RTC from hmi and not from PLC ?
Have you check how N10:0 and N10:1 are being used, are you sure they are not used or modified somewhere else ??


I am not sure why they chose to use the HMI RTC. N10:0 and N10:1 are only being used to execute moves and no where else in the program. I am not sure how N:10:0 and N10:1 are being updated either. cant seem to find the source.

Thanks!
 
What make and model of HMI are you using ?

What function is it using to write the values of its clock into the PLC ?

Is the HMI maintaining its clock internally, or does it update from an external source like a server, or a GPS device, or an Internet time service ?
 
What make and model of HMI are you using ?

What function is it using to write the values of its clock into the PLC ?

Is the HMI maintaining its clock internally, or does it update from an external source like a server, or a GPS device, or an Internet time service ?

it is an panelview plus 600. i have attached a picture of how it is connected to the plc

HMI.PNG
 
I have not had good success with that feature of the PV+, and do not consider it reliable. Future systems that I use the PV+ on that require reliable time service will have a separate time server of some kind.

My recommended diagnostic is to create a display with the FactoryTalk Diagnostic object on it, full-size (or at least as full size as you can with a 6" screen).

You should see all the tags being written to the PLC from the PV+, including these Global Connections. Watch those to see if the PV+ is actually sending the wrong value to the PLC.

I saw a system recently where it was sending "5016" for the year, and the diagnostic window confirmed it really was sending that value. Rebooting got it working again.
 
My recommended diagnostic is to create a display with the FactoryTalk Diagnostic object on it, full-size (or at least as full size as you can with a 6" screen).

You should see all the tags being written to the PLC from the PV+, including these Global Connections. Watch those to see if the PV+ is actually sending the wrong value to the PLC.

i created a window with just a diagnostic object in studio but when i run it im not seeing it sending any values.
 
i have been watching it more closely and the HMI is sending the correct time every 60 seconds and it updates the registry but as soon as it does it reverts back 5 minutes. I see nothing in the program that would make this happen... Very strange
 

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