DCS Safe I/O Alert Triggering When Safe "@SSO[3]=@SPI[9]"

  • Hello,


    I have been having a DCS issue where I am trying to have a simple safety condition where SSO[3] = SPI[9] ( which is an Input from my Safety I/O Conversion Board ). SSO[3] being the Safe System Output for triggering an Ext Emergency Stop when conditions are unsafe, and SPI[9] being connected to my Safety Output on a Safety Relay and connected to a Safety Interlock. It seems that whenever conditions are "safe", meaning both SSO[3] and SPI[9] are ON ( shown as "@SSO[3] = @SPI[9]" in my DCS Safe I/O Connect Screen ), it still will display the alert for SSO[3] "SRVO-408 Ext Emergency Stop" when pressing the deadman switch to try to move the robot.


    Now in regards to the wiring of my Safety Interlock > Safety Relay > Safety IO Conversion Board, I will explain exactly how I am wiring the Safety Relay to the Safety IO Conversion Board. Starting with the Safety IO Conversion Board we have SFDI11 and SFDI21 which makes up SPI[9]. SFDI21 gives out 24V and SFDI11 seems to be the actual input value being read in for SPI[9]. SFDI21 delivers power to a terminal on the top side of my Safety Relay, which will open or close power to the bottom terminal of the Safety Relay. Then, the bottom terminal of the Safety Relay is wired into SFDI11. Essentially in the end I create a loop starting from SFDI21 > top terminal of Safety Relay > bottom terminal of Safety Relay > SFDI11. So, with just wiring this one input I don't think wiring is the issue here in my opinion. I haven't touched or messed with any of Fanuc's boards other than the two terminals for SPI[9] on the Safety I/O Conversion Board.


    We can toggle on and off power (lock/unlock Safety Interlock) to our input on the Safety IO Conversion Board just fine and see the change in status of SPI[9] and SSO[3] immediately. My condition in the Safe IO looks like this "@SSO[3] = @SPI[9]", the @ symbols indicating that both are powered on and are safe. However, upon hitting the deadman switch or fault reset in auto mode in this safe state, the SRVO-408 alert will trigger and the status of my SSO[3] and SPI[9] are both still showing as ON. I wanted to explain this clearly because with just wiring this one input I don't think wiring is the issue here in my opinion. I haven't touched or messed with any of Fanuc's boards other than the two terminals for SPI[9] on the Safety I/O Conversion Board.


    I've also called Fanuc for two weeks straight and they weren't much help in resolving this matter. So, if you have any suggestions or solutions for resolving this issue it would be greatly appreciated.


    Thank you for your time.

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  • You are wiring incorrectly. All safety signals are dual input. There will be 2 circuits you need to close, never just 1. One is 24v and the other is 0v. It should be SFDI11 to 0V and SFDI21 to 24V. You would run each pair through a separate contactor.

  • Okay, the relay I am working with is an Allen-Bradley MSR131RTP (Dual-Channel Safety Relay). The 24V SFDI21 is connected to terminal 13 and delivers 24V through to terminal 14, which SFDI11 is connected to.


    So, what I am understanding is that we should use both channels on the Safety Relay for each of these inputs SFDI11 and SFDI21. There is a second set of terminals I could use for this along side the existing ones 13 (top) and 14 (bottom), which are 23 (top) and 24 (bottom). I could give power to the two top terminals 13 and 23, and then the two bottom terminals 14 and 24 would be connected to SFDI11 and SFDI21. This way it is set up, it will deliver 24V to the two top terminals if conditions are safe aka door is closed/locked.


    Is this what you mean when connecting to two separate contactors? If not, how would I connect it properly?

  • Close but not quite. There should be a 24v and a 0v power terminal on the dcs board. Not signals just power supply that you can use to deliver to your inputs. You will wire it as dry contacts.


    You need to close 2 circuits. 0v power to SFDI11. And 24v power to SFDI21.



    DCS 0v (DC-) to 13.

    SFDI11 to 14

    DCS 24v (DC+) to 23.

    SFDI12 to 24



    When I last wired up DCS inputs, the robot came with a blue cable that plugged into the terminal and had flying leads labeled with 24v, 0v, SFDI11, SFDI21, etc. Just use that to connect to your safety relay as shown above.


    Whatever you do, don't close 24v to 0v :baseball:, you will blow a fuse in the robot.

  • I appreciate your help and clearing up exactly how to wire it, but I am still a bit confused.


    So, we are essentially creating a 24V loop and a 0V loop when both terminals are closed then? Because without any wiring SFDI11 already contains 0V and SFDI21 already contains 24V. Based on what your saying I'd be wiring:


    DCS 0V > 13 > close loop > 14 > SFDI11 0V

    DCS 24V > 23 > close loop > 24 > SFDI21 24V


    Therefore, I would have 0V all the way around through 13 and 14, and 24v on both 23 and 24 which upon making contact could have the current of both supplies added if the polarity is the same. I am saying this because the input of my SPI[9] would never be powered ON if all it reads on SFDI11 is 0V.


    I did still test your way of wiring it for a split second, and SPI[9] never turned on when both loops are closed on the safety relay. I did make sure not to close 24V to 0V (do you mean not to close 24V to the 0V on the power supply area? or the 0V on SFDI11?).


    Should I add the 24V to SFDI11 as well because that seems to power SPI[9] ON from the initial way I looped it? Then for SFDI21 on terminal 24(bottom) should that still receive 24V on terminal 23(top)?

    Note: The Safety IO Conversion Board I'm working with is "A20B-1009-0480/03A".

    Edited once, last by CheckMiniMap: Included Safety IO Conversion Board # for reference. ().

    • Helpful

    Sorry I had a couple typos. It's not 11 & 12. It's 11 and 21 that make a pair for a single safety input.


    It's all covered in detail in the DCS manual.


    Close SDFI11 to 24V


    Close SDFI21 to 0v



    SFDI11 is a sinking input. It measures 0v with nothing connected and you bring it up to 24v.


    SDFI21 is a sourcing input. It measures 24v with nothing connected and you pull it down to 0v.


    The only way you blow a fuse is connecting your power source together. The inputs won't blow a fuse.

  • Thank you for this info! I will make sure to try this on Monday when I am back in work. Hoping this will fix my issue. I'll let you know how it goes :smiling_face:

  • This fixed my issue! I looked through the manual and confirmed the details of this and saw the wiring to what you were describing. Followed the wiring instructions as so and it worked!


    Thank you very much for your time looking into this and helping me resolve this issue, I greatly appreciate it!

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