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jimcav

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new jersey

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• Jan 24, 2018

• #1

ok guys i am having a brain **** I am using a micro logix 1100 i have an n7:1 value if does not change within 3 sec, I need to set an alarm. Thoughts?

Thanks much

 

tarik1978

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• Jan 24, 2018

• #2

you may try this

 

cwal61

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• Jan 24, 2018

• #3

If N7:1 not equal to N7:2 then one shot Move N7:1 Into N7:2

If N7:1 = N7:2 then run alarm timer.

If alarm time done then fault.

 

Aardwizz

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• Jan 24, 2018

• #4

Tarik:

Your code will not work. While the timer is timing (i.e., not DN), N7:1 will always be made equal. Then, when the timer is done, they are equal, and you always get the alarm.

 

Aardwizz

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• Jan 24, 2018

• #5

Lose the one-shot, just in case N7:1 changes before the next scan (I assume this is heartbeat logic, and N7:1 is being messaged; communication is asynchronous to scan).

Instead of the one-shot, RES the timer

 

OkiePC

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• Jan 24, 2018

• #6

Heartbeat logic. I use it a lot.

If N7:1 is equal to N7:2 start the timer TON T4:0. Branch around the EQU with the done bit in series with a reset bit to seal in the rung once it becomes true if this is desirable in your application.

The next rung unconditionally moves N7:1 to N7:2

 

tarik1978

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• Jan 24, 2018

• #7

Aardwizz said:

Tarik:

Your code will not work. While the timer is timing (i.e., not DN), N7:1 will always be made equal. Then, when the timer is done, they are equal, and you always get the alarm.

Click to expand...

Thanks
I missed the one shoot before Mov instruction

 

Aardwizz

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• Jan 24, 2018

• #8

Adding a one-shot doesn't solve the problem.

Timer starts ticking. One-shot fires, making N7:2 equal to N7:1
After one second, N7:1 changes (say).
When the timer is done, the values are different, so no alarm. So far, so good.
Timer resets, one-shot fires, and the two values are the same again.

But N7:1 hasn't changed for 2 sec already. The alarm should fire in just 1 sec of inactivity, but won't until a total of 5 sec has elapsed, and it will "forgive" changes every 4 sec, which was not the requirement.

 

OkiePC

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• Jan 24, 2018

• #9

This is a working example with a 5 minute timeout (with no seal in/reset branch)

I put the MOV on a branch instead of a separate rung because order of execution is important and that will help future editors of this logic from inadvertently moving them out of order.