1/27/2016 8:57 PM | |
Posts: 7 Rating:
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I know we can perform a wire break function on the analog input. Can I do something similar for the discrete input? |
1/28/2016 6:13 AM | |
Posts: 5225 Rating:
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Hi. There are "safety" schemes that is best suited for what you ask. Communication capable devices for example where you receive On/Off state via communication. When some devices switch "off" the signal you receive is not actually off, but rather at a voltage. In this case you could use an analog input instead of digital input and actually read the voltage.. in concept the same as 4 to 20mA. Trouble comes when having a hardware switch. When switched to the off position, you have an open contact which you can not read a voltage from.... it look like a wire break. In this case you could use x2 digital inputs, one to a normally open contact and another to normally closed. In this case PLC logic can monitor for a difference in signal within a short period. Does these ideas help any?
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Last edited by: William_B at: 1/28/2016 4:37:06 PMAdd link.. not useful for answering question but useful for background. |
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1/28/2016 5:22 PM | |
Posts: 7 Rating:
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Great! Thanks. |
3/25/2016 4:02 PM | |
Posts: 4 Rating:
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Normally a 10k resister will be wired across the field potential free contact to monitor a wire break. Is it not suitable to your application? |
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