monitor power loss

kurt.brinker

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Dec 2006
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I am suspecting that one of our slc 5/05's is losing power intermittently. Is there anyway to moinitor or count when this happens? I looked in the S2 file and the is a fault/powerdown section

Rung# S:20 = 0
File# S:21 = 2


Is this saying i had a power failure? If not, how can i monitor it. Right now i am leaving a pc online with the plc and hoping that i get a communication error if it loses power for a second.
 
It sounds like you are looking for a software way to do this but a simple hardware way is to hook up a relay to the power supply.

Get a relay that you can manually operate. Wire a normally open contact in series with the coil and then manually activate the relay.

If the power flickers your relay will drop out and not reset.
 
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From the help

Fault/Powerdown (Rung #) S:20 - (File #) S:21
This is the word and file that the processor last executed before a major error or powerdown occurred.

RSLogix 500 - Copyright Rockwell Software 2000, 2001, 2002
 
You could program a user fault routine

Startup Protection Fault S:1/9
When this bit is set and power is cycled while the controller is in the REM Run mode, the controller executes the user fault routine prior to the execution of the first scan of your program.
RSLogix 500 - Copyright Rockwell Software 2000, 2001, 2002

You could every minute of so copy the time and date to a set of registers and then if the power fails and comes back up then using the User Fault Routine copy the last recorded time and date stamp into a different set of registers (perhaps with indexed addressing etc). This will then give you a record of the last X power failures with time and date stamps.
 
If it is in run mode, at power up; I would think that you could use the first pass bit and a counter, or as Dave said, log the time and date into files if you need that info. The relay thing works well also.

Is your program resetting, or what is causing you to think there is a power failure?

brian
 
well supposedly earlier today, all valves and pumps that are controlled by that plc spontaneously closed/shut off. They say it happened twice and they immediately went to the hmi and were able to restart all of it.
 
al041907.JPG


If N7:0 is any number other than 0 or 1 (it will initialize to one the first time it runs after you install it unless you program it in online in which case it will be 0) then you will know that power has cycled. I think you will want to use an add statement rather than a Counter becasue the prescan sets the counter CU bit so that a counter counts on transiton, not on rung state on the first scan. (I'm not 100% sure on that, but if I recall correctly that is the case)
 
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