How to make Micro800s count down or track the first of the month

JeffreyS

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• Jun 22, 2016

• #1

I would like to have my Micro820 send a modbus message every first of the month just to show the system is up, alive and running properly. I don't think there is a cmos battery like there is in a PC to keep the date/time accurate so I can't trust a get date function.
Would a really long counter do the trick? Suggestions?

 

gclshortt

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• Jun 22, 2016

• #2

http://www.plctalk.net/qanda/showthread.php?t=103322

The above thread is similar to your request. An external timer would be better in the application.

Regards,

 

JeffreyS

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• Jun 22, 2016

• #3

Thanks for writing back and the link! I am going to try and have the RAM controller slave write to the master over Modbus TCP and then have that in return set a bit back in the RAM over Modbus serial from the PLC master. That way a loopback is formed and the whole system is tested upon keep alive.

 

damica1

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• Jun 22, 2016

• #4

I do believe the "DOY" function would do what you need. Make sure the "RTC" is correct.

 

JeffreyS

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• Jun 23, 2016

• #5

Thanks for writing back Damica.
The help states
When the embedded RTC has lost its charge/memory due to loss of power:

• RTCData is set to 2000/1/1/0/0/0.
• RTCEnabled is set to one (1).

So wont that mess up using this as whenever the power goes out it will lose it's place.

 

damica1

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• Jun 23, 2016

• #6

I don't know how long the RTC will retain it's memory after power loss, but it is not immediate. I have several Micro820 in the field that use the TOW function, and there have been times will these unit's loss power due to "Power Utility Problems" for as long as several hours.

You could always install a Battery backup system designed for power problems.

Have a great day.

 

JeffreyS

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• Jun 23, 2016

• #7

I do have a battery backup in the unit! So lets say worse case the power did go out long enough that it died. How can I setup the DOY to just trigger a month from whenever the power comes back. It would mess up the PLC sending it out on the first but that really doesn't matter. As long after around a month it sends it's I'm still alive message out.