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Below in right side there is an discrete output signal circuit implementation and as a platform i need to read this signal somehow. I have a discrete input interface. My question is how can use my open/gnd interface to read signal.

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    \$\begingroup\$ Please explain MSI, ASI and CSI. What are the B and S terminals? What do you mean by 'platform'. What is in the ASI box and MSI boxes? Does the relay contact not tell you the status of the interlock. \$\endgroup\$ – Transistor Nov 21 '15 at 22:04
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    \$\begingroup\$ By the look of your circuit you are already reading the contact status with the Schmitt trigger on the left. It's not clear what you are asking. Do you want another device to monitor the same signal as the Schmitt trigger? If so is it powered from the same supply / a different supply with the same voltage? What is an open / gnd interface? \$\endgroup\$ – Transistor Nov 21 '15 at 22:57
  • \$\begingroup\$ That's a 580 page document and I'm sure it's great reading but life is short ... You need to find out and give us the detaily of the I/O board. Can you mark up on your schematic where you want to attach your circuit and what the voltages are on the relay side and on your I/O board as requested. Where did you get the term "open/gnd"? It's not standard terminology so I don't know what it means. \$\endgroup\$ – Transistor Nov 21 '15 at 23:39
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The terminologies you are using are not common, so here are my guesses.

The big red box you have outlined is by itself an open/gnd detection circuit. So if that is your "discrete input open/gnd interface", then it is all set to just connect to the ASI connector.

The purple circled part is also an open/gnd detection circuit. It is simpler being not having an isolation relay. That may be more likely to be representative of your "discrete input open/gnd interface". By connecting the purple line to the "B" input, it should work functionally without the added isolation and protection of a relay. But if that does not meet some requirements not specified here, then adding the relay (and diodes) may be the way to meet those requirements.

But these are just guess works to move you forward a little bit. You really need to find out the requirements and what the elements (e.g. discrete input open/gnd interface) really are.

enter image description here

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  • \$\begingroup\$ Appreciate your detail explanations and advice Mr. Rioraxe. Thanks. \$\endgroup\$ – Soso5 Nov 22 '15 at 9:29

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