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Erez

RSLogix 5000 A.I issue

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In the configuration of the A.I card (The 1756-IF16 module properties) i can't see any thing to do with what happens in the module (or the analog values actually) if it's pulled out of the slot. In the ladder diagram you use the info that was read from the channel but if the A.I card is no longer available (Pulled out of slot or chassis power failure - on remote chassis) than as much as i know, the variable in which the A.I value was stored to, actually shows the last read value which is a big mistake because the real value no longer exist. Does anyone has any idea on how to solve this problem. I do know that one can clear tha A.I value if a fault bit accurs on an A.I channel. I'm looking more for a basic configuation on how an A.I channel behaves if a card is pulled out of slot or the chassis loss of power. Thanks

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Welcome to the Forum, Erez ! That's an great point. The appearance of the last state instead of zero data is intentional. Rhetorically: If you were a maintenance person, wouldn't it be more useful to have the value that the analog input was reading right before the module failed, or to just have a zero or an unusable out-of-range value ? If zero is sometimes a legitimate value, then you can't use zero to indicate failure. And if you use an out-of-range value, then you risk users writing code that faults the controller when fed an out-of-range value. To monitor the health of modules in the controller's chassis or in remote chassis over ControlNet or EtherNet/IP, the standard mechanism is to use a Get System Variable instruction to read the Module Object's EntryStatus value. You can read the details in the RSLogix 5000 online help under "GSV/SSV Objects". An EntryStatus value = 4 indicates a running and healthy connection. Because the EntryStatus value is encoded in bits 12-15 of this Integer tag, I usually make an "EntryStatusRawValue" the result of the GSV, then divide by 4095 to get the EntryStatus value itself. When you are using Rack Optimized connections there is an easier way; look at the SlotStatusBits DWord for the I/O chassis connection. When the connection to the remote Ethernet module fails, all the SlotStatusBits will turn to 1, making the overall DWord value = -1. This is an easy indication of communication failure to the remote chassis that does not require any extra programming.

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Thanks Ken I was afraid that this is the only solution. I was comparing other PLC's (like seimens) which offer other solutions. Erez

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It is really a tiny amount of effort. Three instructions, three tags, one rung. In the case of a Rack Optimized connection (the most common kind) it's one instruction, or zero if you are using an HMI. What I would prefer is a Module-created tag called ConnectionStatus, but I understand that extra status features mean extra overhead, so I'm willing to build my own connection monitoring logic.

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Thanks Ken I was afraid that this is the only solution. I was comparing other PLC's (like seimens) which offer other solutions. Erez

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