Big Error

Sparky

Member
Join Date
Jan 2003
Location
Twin Falls, ID
Posts
64
I made a big mistake today. :sick: I was wondering if any body else has had BAD days? I tripprd a CB by plugging in a shop vac, to clean up a work area, into a outlet supplied by a 5 amp CB. Yes I knew this was stupid at the time, Operator level of stupidity. banghead Of course it tripped and the CB also supplied the voltage to about 7 output cards. The outputs(valves) dropped off-line but the 40Hp pumps that are controled by a different SLC 500 kept running. I made a BIG mess, one that cost alot of money and time. I probably won't live this one down for a long time. Just to make me feal better anybody else have a bed day like this??? :oops:
 
Not today,but.......

About a month ago I killed two 36" long servo-driven linear actuators. We have a gap assembly that is driven on both sides by independent linear actuators. I have one set up as a master and one as a slave. The master gets a velocity command from a plc. The slave gets an encoder output from the master as a position reference. Usually this works pretty well.
We also have a magnetostrictive linear position transducer on each actuator body to give us actual position. The idea was to check the two feedbacks against each other and shut down if the positions got outside a set value. Well, you see, we had trouble early in testing with one of the magnetostrictive transducers so we just increased the position mismatch window so the bad sensor didn't shut us down. This was forgotten when the machine was put into production. The master decided to move and the slave didn't. This twisted our gap assembly up pretty nicely and bent the linear actuators up to the point that they didn't work anymore.
So not only did we need to by new linear actuators the customer was down for about 2 weeks waiting for new ones.

Keith
 
If the valve status is critical to whether the pumps should run or not, the pump logic should be interlocked with the valve status.

Is there any communication (or discrete I/O) between the SLC's that run the valves and pumps?

You should not have plugged a large load into the receptacle, but on the other hand, the process should have stopped if there was a major problem such as this...
 
Doesn't sound like your fault at all to me. It sounds more like poor design. A 5A cicuit breaker supplying 7 output modules should not have had a recep on it as well. Seems to me the same mess would have occured had the CB tripped for another reason or if the plc faulted. For something like you described, both plcs should have had some sort of communications to prevent that from happening. Even if it was something as simple as each plc providing the other with a discrete input from the other's output showing that it was "live".

It is fortunate that no one was hurt or killed.
 
I was debugging a robot, it stalled after loading a dryer, the company owner walked up, I found the stall and fixed it as the dryer lid was rising, as the lid was safely down when the request to move was initiated the robot took off into the dryer lid scaring the owner half to death and making a big mess of twisted metal and plexiglass. All while another programmer was on the phone explaining that the robots never hit anything to a customer.
 
If you are in this business long enough, you will make a few mistakes.
The ones that dont are professionals (been around for awhile) or they just sit on there a$$ all day and do nothing.
 
Great topic!!

Late on a Friday, my troubleshooting skills were... well... OK I was retarded.

I had an output that wasn't working so I assumed a single blown output. I grabbed another output module from the same rack and stuffed it in. (Here's the only weird part I still can't figure out) It worked! So I grabbed a new one from the cabinet and stuffed it in. SMOKED!!! Yep, a little pillar of smoke rose out from within. The magic smoke escaped.

Clearly that new module was bad from the beginning so I grabbed another. Yep, smoke. I'm still waiting for the relay cards this module feeds 'cuz if ya' fool me once shame on you if ya' fool me twice shame on me. :oops:

I'll get it figured out here shortly.
 
What Mike said.

Someone here or maybe on another forum I visit I think has a signature that reads:
Experience comes from poor judgement
Poor judgement comes from lack of experience.

We all make mistakes...some of us alot.

I do think the worst part of that was having a 15amp outlet on a 5A breaker especially if that breaker powered other things. The outlet should have been on its own 15A circuit. Its not to late to change it, or remove/disconnect it.
 
We have 145 CNC machines and all have a receptacle for LAPTOP USE ONLY. I wish I had a dollar for every time someone plugged a shopvac, drill, or grinder into them. Luckily all of ours only supply the receptacle and maybe the electrical cabinet lights.

We've all had close calls and absolute disasters. The only way to ensure it never happens is to sit on your A$$ and do nothing.

The hard part comes in explaining what/how it happened. :)

Bob
 
Sparky,

I think you've only made a big mistake if you and your company fail to take steps to prevent something like this from happening in the future. It sounds like it was an accident waiting to happen. You just happened to be in the wrong place at the wrong time.
 
A few years back, commissioning a huge vacuum lead dust transfer system, after many days where any mistake from my part meant emptying the whole system (1000' of 4" pipes full of toxic metal). I was finally done.

So all that was left for me to do was to disconnect my laptop and leave. Simple enough?

I pulled on the laptop power cord. It did not come nicelly out of the power socket. The laptops power cord leed fell down, touched on a 600 Volts motor terminal.

The jolt of tension whent through my power cord, my laptop, my rs422 PCMCIA card, into the PLCs CPU, onto the racks BUS. Out of the montion control module and through the servo drive amplifiers into the ground.

Results, 5 days downtime. CPU, 10 I/O cards, analog modules servo drive amplifiers and of course my laptop and serial card. All out of MY pockets.

NEVER AGAIN.

PS: And it was friday afternoon
 
Last edited:
I'd agree... Unless the guy responsible for the recent blackout posts his story, Pierre's will probably be the biggest "Oops" we'll hear about.

I had a pretty good 'no screw-ups' streak going for a while... Until a few weeks ago... banghead

I had a Kollmorgen servo drive temporarily powered up on the bench for testing. At this point it was wired correctly (and functional). Then I had to 'borrow' the power cord to test something else. When I finally got back to working on the servo drive, I mistakenly rushed during the reconnection and offset the connections by one terminal on the terminal strip. The terminal strip was laid out like this:
[attachment]
I remembered that it connected to the bottom 4 terminals, but forgot that the ground connection was NOT on the terminal strip, but rather a separate stud below the terminal. So, instead of connecting L1 to L1, L2 to L2, L3 to L3 and Ground to Ground (the stud), I connected L1 to C, L2 to L1, L3 to L2, and Ground to L3.

Needless to say, the distinctive Ka-BOOM when I applied power meant that I now owned a $1200 paperweight... :oops:

No smoke, but it now rattles when you shake it due to the new 'free range' components that were violently 'dislodged' during the mishap... šŸ™ƒ

beerchug

-Eric

servodrive.jpg
 

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