Fault Logic

[jamorenos]

Hi there,

I am trying to create a Fault Logic, the scenario is 2 chains that should be running essentially at same speed. I have 2 proximity sensors reading a chain dog on each chain, the dogs have to be sensed at same time to be NO Fault, if they are not sensed at same time this should trigger a Fault and I will use this to stop my system. Obviously conditions that could happen are Chain Dog #1 sensed before Chain Dog #2 and vice-versa. I am using Contrologix PLC V20 with RSLogix 5000, Any ideas ? Thanks for your feedback

 

[James Mcquade]

Welcome to the forum.

Are the 2 chains driven by the same motor, is one driven by the other?

Have you considered the load on each chain, stretch factor?
A few more details are really needed.

james

 

[Steve Etter]

It's been my experience that things happening at "the same time" rarely happen at EXACTLY the same time; usually there is some acceptable variation.

That said, I would create two timers; one that looks for the first dog to start it and the second to stop it and the second to look for the opposite (second dog starts, first dog stops). Set your timer presets to the allowable variation time and then, so long as neither timers ever time-out (ie. both dogs are seen within the preset time) all is good. If either timer does time-out, though, you have your alarm.

 

[rdrast]

Use the dogs to determine the velocity of each. If the velocity deviates by some set amount, trip your fault.

 

[JerryH]

Could something like this be used to make sure the dogs make the sensors within a certain amount of time. This could be modified to look at the leading edge of the dogs if wanted.

 

[jamorenos]

Welcome to the forum.

Are the 2 chains driven by the same motor, is one driven by the other?

Have you considered the load on each chain, stretch factor?
A few more details are really needed.

james

Thanks James yes they both are driven by same motor

 

[Caveman]

How about just using anti tie down logic.

 

[jamorenos]

Thanks all for the feedback, the Timer solutions seem to be right, any other suggestion?

@rdrast : could you explain more your concept when you say velocity, how would you do this.

Thanks again

 

[jamorenos]

How about just using anti tie down logic.

Thanks Caveman for the reply

I am a little confused, I have used Anti-Tie down when for example you have a semi-automated machine where the operator need to use both hands (so that these are clear from machine) to start the cycle. In my understanding the Anti-Tie down expects to see both input signals to start a cycle, in the chain dog application what if the chain dog #2 comes 1 second after chain dog #1, condition will never be true, am I right?

I don't see how I can use it to check if both chain dogs are sensed at same time to trip the fault.

 

[jamorenos]

Could something like this be used to make sure the dogs make the sensors within a certain amount of time. This could be modified to look at the leading edge of the dogs if wanted.

Would you use an OSR to look for a leading edge? Could you send an example?

Thanks!!

 

[Caveman]

and vice-versa.

That is how anti tie down works. The timer setting will be the range of too far out of adjustment.

 

[ASF]

Nice and simple:

|    Sens_1    Sens_2               
|-----| |-------|/|-------+---------(TMR)--|
|                         |
|    Sens_1    Sens_2     |
|-----|/|-------| |-------+
|
|     TMR                           Fault
|-----| |-----------------+---------(   )--|
|                         |
|    Fault     Reset      |
|-----| |-------|/|-------+