I/O module's test signal terminals

unsaint32

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Oct 2012
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minneapolis
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Some safety relay I/O modules have test signal generators. For example, Sick Safety Controller's I/O module has two safety signal generaros, X1 & X2. Many I/O modules have these test signals. What are these test signals? Can someone describe some applications that can explain why it is called "test" signal? Thanks.
 
These are outputs that switch on and off at certain frequency. When a safety device, like an E-Stop button contact, is connected between such a "test" terminal and a "safe" input, the safety controller expects to read the same pulse pattern back. This indicates the integrity of the safety circuit and adds a degree of reliability as compared to a circuit where e-stop is wired just to a DC power bus.
 
These are outputs that switch on and off at certain frequency. When a safety device, like an E-Stop button contact, is connected between such a "test" terminal and a "safe" input, the safety controller expects to read the same pulse pattern back. This indicates the integrity of the safety circuit and adds a degree of reliability as compared to a circuit where e-stop is wired just to a DC power bus.
I see, it's sort of like the flashing LED for network Link status. Makes sense. Thanks Ladderlogic.
 

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