Shorting out a OB16E output card

I need to internally short out an OB16E allen Bradley output card. What I need to know is how long it takes for the fuse to reset itself after a short or surge in the card.

I tried jumpering 24VDC to Common, but cannot get the Efuse to activate.

Thoughts?

The electronic fusing does not reset itself... the design assumes something is wrong that needs human rectification before it is manually reset via the programming software.

However, it is possible to write code to reset the fuse, but how do you know if the cause of the overload has been removed ?

You shorted out supply to common... that is not what the electronic fusing is for.... Each output channel has an electronic fuse that goes high impedance when an overload condition is detected (say a short-circuit in the field). It stays high impedance until reset as above.

Auto Reset

I am reading in this article from Allen Bradley about this particular output card and it states "The 1746-OB16E modules perform auto-reset under overload conditions. When an output channel overload occurs, that channel will limit current within milliseconds after its thermal cut-out temperature has been reached. While in current limit, the output channel can cool below the thermal cut-out temperature allowing the module to auto-reset and resume control of the output channel as directed by the processor until the thermal cut-out temperature is again reached."

Reason I am asking is because of an issue that arrised at one of our customers facilities on a machine of ours.

We have a cognex Barcode Reading system installed on this output card, and they had experienced a power outage for 12 minutes during the night shift. It was during power-up when we noticed the cameras were unresponsive. I could manually trigger the camera using the setup tool provided, but that is over ethernet, and not discrete I/O which is what we currently have set up. We use messaging commands to activate certain functions in the camera through Dataman Command Control (DMCC) from a SLC 5/05, and also message to a Control Logix L73 Processor to get ok to run signals from their process side of the system.

What happened is the cameras became unresponsive for a period of about 8 hours. I reloaded the config files, and did some hard resets on the camera to no avail. It was about 40 minutes after I did all these tests, that the cameras, on their own, started to function again for no particular reason that I can think of, other than the card reset itself after it reached a safe operating temperature.

This is why I need to test the response time of the card and see how long it would take to reset itself. I am mimicing the environment to the best of my abilities.

So can someone help me figure out how I can get this EFUSE to trip so I can determine an approximate reset time on this card so I can try to narrow down this issue?

Cognex engineers have never even heard of this issue before, and I know they are passing this on up the ladder to see if they can give us an explaination as to why this happened.

Thanks for the future input!

My information was presented about the 1756-OB16E, I see now that you are referring to the 1746-OB16E.

Anyway, to "trigger" the module's electronic fusing, you need to create an overload (high current) on an output terminal, which you could do by just shorting out the load it is driving, because that is what the module is designed to protect against.

In theory, you could just place a high load (low resistance) from the output terminal to common. When the output is turned on by the program, the thermal cut-out will operate within xxx mS, turning off the output. Then the thermal cut-out will cool down, allowing the output to come on again. Monitor the output with an oscilloscope to see the timing. I doubt very much that the thermal cut-out will need more than a few seconds to cool down and allow the output to come on again, I can't see it needing 40 minutes !!