AB 500 Timer

whiggins

Member
W
Join Date
May 2006
Location
Princeton, KY
Posts
26
Hello I have a SLC 500 1747-L40B. I have programmed a timer and when it goes done it is done. When I use EIO contact with the same address as the timer it does not reset itself??? First time I have ever seen this prob. Any thoughts?
 
Do you mean "XIO". Did you you use the "DN" bit?

Post your code if you can.
TestTimer.jpg
 
are you sure that you're using a TON timer? ... the TOF and the RTO timers work differently ...

also make sure that you haven't "reused" a timer address that's used on another rung ...
 
it might LOOK LIKE the bit never came ON when you look at the screen (or an output in the field) ... that's because the Done bit is only ON for ONE very brief scan ... that's not enough time to see anything "come on" in the field ...

try experimenting with an LES or GRT comparison statement ... have it look at the timer's accumulator and go from there ...
 
Are you using the done bit in an uncalled subroutine.
Post your code. We will help you look for the problem.
 
When the done bit goes done it never resets the TON so that it can keep counting. That is how I know it must not be going DN. After the TON reaches the preset the timer shows dn but it never restarts. I will try your comparison later. I am teaching class right now. Thanks
 
Mickey not sure what you mean by code? As far as I know I am not using a sub routine. To test the plc I used the ladder rung you posted and it does not reset itself.
 
I've got a hunch that we're just not understanding each other ... can you post the .RSS code? ...

edit ... Mickey and I are "posting-over" each other ... save the program ... this will give you an .RSS type file ... use WinZIP etc. to zip the file and then attach it to a post ...
 
Last edited:
I just looked at PLC again. I have XIO reseting a TON on rung 1. On rung two I'm using a XIO (dn) to control a contactor. The done bit is changing from 0 to 1 on data table but the contactor never go off.
I put a switch on rung 1 and manually reset timer and it works?

Another thing that is happening is I am using it to turn on and off neon bulbs and they stay about half lit all the time? (getting 70 vac on output) Do you think the triac is shorted???
 
If you are using an XIO to control your contactor it is only open (off)
for one scan ( proably low milliseconds) which is not long enough to shut off the contactor.
All solid state devices leak a little.
 

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