Dumb Question

Tarheel

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Join Date
Jun 2007
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Ma
Posts
14
I have a problem in my logic circuit that I think should be easy but can't figure it out since i now have 3 days of programming experiance.

I'm setting up a system thats getting an input from another sort of sensor, and my problem is that my PLC is seeing what should be one pulse as a couple of pulses, I want to fix this by saying that once the PLC recieves an input to not pay attention to any more inputs until 100 ms passes. The only way I can think of enacting this at the current moment delays my entire process, which I don't want to do.
 
Not a dumb question. What kind of PLC are you using? what kind of sensor? what is the application? Probably what you want is a debounce timer but without more info it is hard to say.
 
I'm using a Allen Bradley SCL 500 1747-L531 and RSLogix 500, I actually don't know that much about the sensor other than it applies approximentally 25 V to my input for 5 ms or so, I'm using this for a diverting application so when there is a piece I want the sensor applies the voltage.
 
Tarheel said:
I'm using a Allen Bradley SCL 500 1747-L531 and RSLogix 500, I actually don't know that much about the sensor other than it applies approximentally 25 V to my input for 5 ms or so, I'm using this for a diverting application so when there is a piece I want the sensor applies the voltage.

Do you mean something like this ?
SENSOR.JPG
 
How do you know that the sensor "applies approximentally 25 V to my input for 5 ms or so"? That might be faster than the SLC's scan time.

One solution might be to have the input latch an internal and use a contact from the internal to start a timer. The timer's DN bit unlatches the internal. Use a contact from the internal instead of the input signal in your logic.
 
Danocane said:
Danocane __________________
There is One Firearm for every 12 people in the world. My question is: How do we arm the other 11?

Danocane

I like that. Where did the 1 in 12 come from? I guess I'm just selfish cause I throw that average all to heck. Which means that many more you have to find guns for, cause I aint givin none of mine up.


-jeff
 
Firearm Distribution

That line came from a Nicolas Gage movie where he played an arms dealer. I am afraid that I have more than my fair share also.
 
Tarheel said:
I actually don't know that much about the sensor other than it applies approximentally 25 V to my input for 5 ms or so,
This looks like a problem to me. I have several units where I work that wouldn't see this short pulse.

allscott said:
what kind of sensor? what is the application? Probably what you want is a debounce timer but without more info it is hard to say.

I think we also need input module info as well as scan time. I also need to enforce Allscott's request for sensor info.
 
Are you sure 5ms?

The difference between 5ms and even 20ms (for example) is quantum for PLC control.

You need to find out the turn on time of your sensor, the turn on time of your PLC input card and the scan time of your PLC. Even just post the part #'s, that will help.

If this was 500ms these timing aspects probably wouldn't be an issue but if things are really happening that fast then they are.
 

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