adccommunitymod (AutomationDirect) asked a question.
Created Date: March 20,2015
Created By: ericn
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On a recent machine, I used two LPC-110005 safety switches wired in series to an LG5925-48-61-24 safety relay. Everything worked fine. The customer asked us to add an additional access door on the machine, so I installed one more LPC-110005 in series with the other two. Everything works for a few door cycles, then the newest switch suddenly stops working. No light when the door is closed, and neither of the contacts are closed. This happens regardless of what door is opened. In other words, I can open and close the first or second door, and suddenly this new switch on the 3rd door stops working. I have replaced the switch, but am still having the exact same issue. The only way to get the switch working again is to cycle power to it (red and blue wires). Then it works again for a short while. Do these switches have some type of internal fault monitoring that requires a power cycle to reset? I might suspect too much voltage drop in the circuit, but it seems odd that this would be an issue with only 3 switches in series. I normally use tongue interlock safety switches, so I don't have previous experience with these coded magnetic switches. Any ideas as to the cause, and/or a solution? Would the non-coded switches be better, as they do not require an external 24VDC supply? Thanks, -Eric
Created Date: March 20,2015
Created by: kewakl
The sensor pdf file indicates three coded switches into a SCR-2 or SCR-3 safety relay.
It seems that the sensor and relay are different brands, so three sensor arrangement may be for the IDEM relay and not the DOLD relay.
Are you connecting the sensor wires as per the attachment?
Created Date: March 20,2015
Created by: ericn
The specification sheet confirmed my suspicions about polarity. I should really read these things more often :p
I should be all set for tomorrow!
-Eric
Created Date: March 20,2015
Created by: Adisharr
I would add that on some units, if the switches have a series LED indicator light then wiring more than a few of them in series will drop the voltage enough to cause issues. I 've run into that a few times.
Also, if you 're required to pay attention to category / performance level in this application then wiring more than one set into an input will most likely drop your performance level. Not a big deal for most but this has been becoming a pain the butt lately with the new regulations.
Created Date: March 24,2015
Created by: ericn
Unfortunately, it's still doing the same thing :(
It's always this third switch in the loop that randomly craps out. The light on this switch stays off, while the other two continue to operate normally. Like I stated before. the only way to make it work again is to cycle the 24VDC supply. I did check the voltage drop across all three switches, but there is barely any (a few millivolts maybe).
As a test, I swapped the wires from switch #1 with switch #3, so the first switch is now the last one in the circuit, and the 'dying ' switch is at the beginning of the loop. Now I just have to wait and see which switch craps out, #1 or #3. This might help me isolate the problem.
I am wondering if location might have something to do with it? The switch that is shutting off is about 2 feet away from a servo motor, but the servo motor cables are fully shielded (factory-made cables), and properly grounded. I normally wouldn't foresee any problem with this, but at this point, I'm not ruling out anything...
It still frustrates me that two switches in series work just fine, yet once I add this third switch, it randomly stops working.
Perhaps switching to the non-coded version of this switch (LPR-11013) might be better?
-Eric
Created Date: March 20,2015
Created by: ericn
On a recent machine, I used two LPC-110005 safety switches wired in series to an LG5925-48-61-24 safety relay. Everything worked fine. The customer asked us to add an additional access door on the machine, so I installed one more LPC-110005 in series with the other two.
Everything works for a few door cycles, then the newest switch suddenly stops working. No light when the door is closed, and neither of the contacts are closed. This happens regardless of what door is opened. In other words, I can open and close the first or second door, and suddenly this new switch on the 3rd door stops working.
I have replaced the switch, but am still having the exact same issue. The only way to get the switch working again is to cycle power to it (red and blue wires). Then it works again for a short while. Do these switches have some type of internal fault monitoring that requires a power cycle to reset?
I might suspect too much voltage drop in the circuit, but it seems odd that this would be an issue with only 3 switches in series. I normally use tongue interlock safety switches, so I don't have previous experience with these coded magnetic switches.
Any ideas as to the cause, and/or a solution? Would the non-coded switches be better, as they do not require an external 24VDC supply?
Thanks,
-Eric