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Old February 16th, 2015, 04:37 AM   #1
JPFX
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Arrow Programming Help

Hi,
I am trying to figure out how to achieve the following logic:

I have two inputs and 1 output
I need the output to be on ONLY when BOTH inputs are on
I need the output to be off ONLY when BOTH inputs are off.

I can't figure this one out, please any help will be much appreciated.

Thanks.
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Old February 16th, 2015, 05:04 AM   #2
JordanCClark
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People are kinder to posts like this if you can show what you've tried so far. This sounds like a homework question and it raises a flag or two. Not that we don't want to help, but we won't do the homework for you...

I'll reword the question to give you a hint.

You want to seal an output on when both Input1 AND Input2 are on, and stay sealed as long as Input1 OR Input2 are on.
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Old February 16th, 2015, 05:31 AM   #3
Sherlock4me
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Quote:
Originally Posted by JordanCClark View Post

seal an output on when both Input1 AND Input2 are on,

and stay sealed as long as Input1

OR Input2 are on.
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Old February 16th, 2015, 06:15 AM   #4
geniusintraining
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Quote:
Originally Posted by JPFX
I can't figure this one out
Here you go...

Code:
A  I  0.0
A  I  0.1
= Q  0.0
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Old February 16th, 2015, 08:41 AM   #5
DwSoFt
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This is and easy one. AND refers to series contacts. and OR refers to parallel contacts. basically each switch will be used twice in your rung. and then there is a seal in as mentioned above. here is a basic start / stop with sealin contact from the output:
-----I\I---------I  I----------O---
I I
I-----I I-----I

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Old February 16th, 2015, 08:43 AM   #6
jrwb4gbm
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Sometimes an example explains things better, see attached.
Attached Files
File Type: pdf Simple Logic Gate.pdf (5.7 KB, 36 views)
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Old February 16th, 2015, 08:49 AM   #7
mk42
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Quote:
Originally Posted by JPFX View Post
Hi,
I am trying to figure out how to achieve the following logic:

I have two inputs and 1 output
I need the output to be on ONLY when BOTH inputs are on
I need the output to be off ONLY when BOTH inputs are off.

I can't figure this one out, please any help will be much appreciated.

Thanks.
The question I have is what is supposed to happen when only one input is on? You didn't specify it was supposed to be a sequence, so that leaves us with undefined states.
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Old February 16th, 2015, 10:19 AM   #8
daba
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Quote:
Originally Posted by mk42 View Post
The question I have is what is supposed to happen when only one input is on? You didn't specify it was supposed to be a sequence, so that leaves us with undefined states.
I'll also state that the two "requirements" are conflicting, and the way they are written neither can be achieved without making the other a nonsense.

In more detail....

1. "I need the output to be on ONLY when BOTH inputs are on"

The highlighted text above is clear and precise, the output should only be on if both inputs are on, so by inference, if either one of the inputs are off, then the output must be off.

2. "I need the output to be off ONLY when BOTH inputs are off.

This second requirement is also clear and precise, the output must be off only if both inputs are off, but this is a contradiction to the first requirement, which stipulates that the output must not be on (must be off) if any one of the two inputs are off.

Clearly the person setting these requirements lacks a good grasp of grammar, by using the phrases "to be on" and "to be off", instead of the phrases "to come on" and "to go off". Only when those changes are made to the specifications can the logic be correctly produced.
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Old February 16th, 2015, 10:39 AM   #9
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I'll also state that the two "requirements" are conflicting, and the way they are written neither can be achieved without making the other a nonsense.

Excellent point, daba.
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Old February 16th, 2015, 11:31 AM   #10
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There I go assuming something again. Good point
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Old February 17th, 2015, 08:26 AM   #11
osmanmom
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do you still need a help

post you program no matter whether is right or wrong
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Old February 17th, 2015, 04:58 PM   #12
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Quote:
Originally Posted by osmanmom View Post
do you still need a help

post you program no matter whether is right or wrong
Unless the original requirements are re-written, no amount of help you could give would be able to solve the inherent dilemma imposed by them.
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Old February 17th, 2015, 06:05 PM   #13
bernie_carlton
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Let's ask Schrödinger's Cat about the other two states.
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Controlling outputs is the PLC's way of getting its inputs to change.

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Old February 17th, 2015, 06:18 PM   #14
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Originally Posted by bernie_carlton View Post
Let's ask Schrödinger's Cat about the other two states.
He's dead... Or is he ?
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