Author Topic: Help with Proximity sensors  (Read 6201 times)

todd432

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Help with Proximity sensors
« on: February 27, 2015, 09:51:54 AM »
Hi all
So I am down to hooking up my proximity sensors
I have 3 wire (brown, black, blue) Inductive sensors NPN NO (detect metal)
I thought this would be pretty straight forward according to page 23 figure 5 NPN Style of the PMDX 126 c manual.

But NOOOO it aint happing, Iam at my wits end trying to figure this out.

It should be pretty easy but when I hook up per fig. 5 the LED lights up on 12 of the BOB, and when I trigger the sensor the led gets brighter on the BOB.If I unhook the black wire the led is ever so faintly still on.

I have the brown wire hooked to the +12U on J12, blue to GND, black to ?12? There is an led on the sensor that lights when I hold it close to metal.

I took a pix of my proximity switch and a wiring diagram of the switch.
Any help or thoughts
Todd
« Last Edit: February 27, 2015, 04:52:10 PM by todd432 »

Steve Stallings

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Re: Help with Proximity sensors
« Reply #1 on: February 27, 2015, 12:43:11 PM »
We have seen this sort of problem before, especially with the
tiny little 4mm sensors. The problem results from the fact
that the sensor has leakage current from the positive supply
coming out of the signal lead even when it is supposed to be
off. For a simple load like a relay this is not a problem, but
we designed a universal input on the PMDX-126 that works
with either NPN or PNP sensors. The leakage tricks the input
in thinking is sees a PNP sensor that is trying to turn on.

That being said, the LED on the PMDX-126 should still go
completely off when you disconnect the black wire.

There is a work around that will let the PMDX-126 work with
an NPN sensor with leakage. You need to connect a 470 ohm
resistor from the black signal lead (on terminal "12" in your
case) to the +5V terminal on J12 of the PMDX-126. This
will swamp out the leakage by diverting it into the +5v
terminal. Do not try to put this resistor to GND as this will
look like an NPN sensor turning on.
Steve Stallings
www.PMDX.com

todd432

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Re: Help with Proximity sensors
« Reply #2 on: February 27, 2015, 04:01:11 PM »
Thanks Steve

Should have know it was to good to be true, 5 sensors for $12 buxs.

Steve do you recommend 8mm sensors  that I read in another post to pervent the leakage?
Its just their $21 buxs ea. I guess you get what you pay for.

Whats another $100 + buxs

Do you allow users to post pixs of their controllers?

THX
Todd

Steve Stallings

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Re: Help with Proximity sensors
« Reply #3 on: February 27, 2015, 06:22:38 PM »
The resistors should fix the problem and only cost a few cents each.

The leakage does not pose any sort of risk of future failure, so running
your current sensors with the resistors is not a problem, if it works.

There is a separate category called "Show and Tell" that is intended
for users to show their builds and other projects. It is at the bottom
of the list of categories. Photo attachments are allowed and encouraged.
Steve Stallings
www.PMDX.com

todd432

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Re: Help with Proximity sensors
« Reply #4 on: March 06, 2015, 03:35:30 PM »
UPDATE

Steve the resistors worked just fine, I needed two to make auto squaring work.
One on screw 12 and 13 , both hooked to the +5 screw (J12)

Thanks, your the man!!

Todd
« Last Edit: March 06, 2015, 08:11:52 PM by todd432 »