PMDX-126 NPN-NO Proximity Switch Problems

[Techsavvy34]

I'm trying to wire my three proximity switches to my pmdx-126 to use as home switches. These are the switches I have:  http://www.amazon.com/SN04-N-10-30V-Approach-Inductive-Proximity/dp/B004V6PTKA
My switches run on 10-30v and have 3 wires.  I connected the three black wires to pin 11,  the three brown wires are connected to positive on a external 24v power supply and the three blue wires are connected to the ground terminal next to terminal 11.  I also ran a jumper wire from the power supplies ground to the same ground terminal that the blue wires are connected to.  I setup Mach3 and if I have active low selected then the leds on the proximity switches are always on and if I put a piece of metal in front of one sensor then all the sensors leds get brighter.  Also on the diagnostics page in mach3 I noticed that M1 Home, M2 Home, and M3 Home are always lit even if metal is in front of a sensor.  If I don't have active low selected the leds on the sensors are still always lit but the M1 Home, M2 Home and M3 Home diagnsotic leds aren't but they still don't respond to metal.  When I tested the sensors individually with my bench power supply they worked fine.  If anybody has any suggestions that would be great.  The only reason I'm using an external power supply is because I was planning on using PNP-NO sensors but then I bought these.  Should I try powering them off the PMDX-126?

[Bob at PMDX]

I cannot quickly find a manual or catalog page that verified the wire color coding, so for now I'll presume it matches the standard color code.

I am guessing that the LED in the proximity sensor is causing enough leakage current into the PMDX-126's inputs that the PMDX-126 thinks is has PNP sensors connected and that they are active (trying to pull the input up to 24V).  If you have a volt meter or DMM handy, you can verify this by measuring the voltage between the "Pin11" screw terminal and the "GND" terminal.  If you see a voltage somewhere around 9 volts or higher (I don't remember the exact threshold) or higher with no metal present then that is the issue.  You can also look at the LED on the PMDX-126 next to the "Pin11" terminal.  If that is on (lit) all the time then leakage current is the issue.

Try connecting one of the sensors to the "Pin15" input terminal on the PMDX-126, and then change jumper JP5 to the "on" position.  Configure one of the Home inputs in Mach3 to be assigned to pin 15, active low.  With no metal present, the LED on the PMDX-126 at the "Pin15" terminal should be off and Mach3 should show the that home signal as in-active.  With metal present then the LED at the "Pin15" terminal should be on Mach3 should show that the home input is active.  Note that the LED in the sensor itself may remain lit all the time.  That is OK as long as the PMDX-126 input

If the sensor works on the Pin15 input, you can either connect all of the prox sensors to pin 15 instead of pin 11 and see if the input still works, or you can get a 470 ohm, 1/4 watt or 1/8 watt resistor and connect it from the '"pin11" terminal to the "+5V" terminal on J12.

You can try powering the prox sensors from the "+12U" terminal on J12 of the PMDX-126.  The PMDX-126 should be able to provide enough power to run the sensors (presuming you aren't powering anything else from the "+12U" or "+5V" on connectors J11 and J12).  I don't know if that will make the inputs work, but it might be worth an experiment.

Bob

[Techsavvy34]

I hooked up a 470 ohm resistor from pin 11 to +5v terminal.  When I power on the board the led on pin 11 is lit but on the mach3 diagnostics page the M1 Home, M2 Home and M3 Home input signals aren't lit.  When I put a piece of metal in front of a sensor the led for pin 11 on the pmdx-126 gets brighter and the M1 Home, M2 Home and M3 Home light up.  It seems that the resistor helped but should I be worried that the led for pin 11 is always on?  Since three sensors are hooked up to input 11 should I use a bigger ohm resistor?   Thanks for your help Bob.

[Bob at PMDX]

Even though Mach3 is showing the correct input response, having the LED on the PMDX-126 for the "Pin11" input staying on all the time, even at varying brightness, is not good.  That means that the input circuit on the PMDX-126 is not fully switching off.  And while it works today the internal voltages are marginal and it may very well not work tomorrow.

Did you try the 470 ohm resistor with 1 sensor connected to the Pin11 input or with all 3 sensors connected?  If you ran the test with all 3 sensors connected please remove 2 of the sensors and run the test again with only 1 sensor connected the to Pin11 input (the other sensors can still be connected to the power supply and ground, just remove the black signal wires from the Pin11 terminal on the PMDX-126).

If having 1 sensor connected along with the 470 ohm resistor to +5V works (i.e. the Pin11 LED On the PMDX-126 turns off with no metal present and on with metal present), try again with the 1 sensor connected and without the 470 ohm resistor.

Do you have input signals connected to the Pin12 and Pin13 inputs on the PMDX-126?

Bob

[Techsavvy34]

I tried the resistor with all 3 sensors connected to pin 11.  The leds on my sensor are always on and just like the led for input pin 11 when metal is present they get brighter.  The leds on my sensor should be off and only turn on when metal is present.  I'll try it with one sensor connected and see if it works.  My only problem is that I have an external cycle start button wired to pin 12 and a hold button wired to pin 13.  I want to keep pin 15 open for future use.  Since i'm using a Smooth Stepper I could connect my cycle start and hold buttons to inputs E and F on the secondary status input connector (J11) right? 

[Bob at PMDX]

I tried the resistor with all 3 sensors connected to pin 11.

OK, please try with only 1 sensor connected (and powered from your 24VDC power supply).  Then also try testing with 1 sensor connected and power the sensor from the PMDX-126's +12U supply on connector J12.  See if that makes the sensor's LED turn all the way (or most of the way) off when no metal is present at the sensor (and see if the PMDX-126's input LED turns all the way off).

The leds on my sensor are always on and just like the led for input pin 11 when metal is present they get brighter.  The leds on my sensor should be off and only turn on when metal is present.

Yes, *ideally* the sensor's LED should be all the way off when no metal is present.  However, the PMDX-126 input's pull-up resistor to +5V will always allow *some* current to flow though the sensor LED (from the sensor +24V to the PMDX-126's +5V).  If we can get the leakage current low enough the PMDX-126's input circuit will work even if the sensor's LED never turns all the way off.  And maybe we can even get the sensor's LED to turn off.  But yes, having the sensor LED remain "on but dimmer" makes visual diagnosis more difficult.  That is apparently the trade off needed due to the design of the sensor's output/LED and the PMDX-126's input circuit.

Since i'm using a Smooth Stepper I could connect my cycle start and hold buttons to inputs E and F on the secondary status input connector (J11) right?

Yes, as long as you have a second ribbon cable to go from the SS port 2 to the PMDX-126 port 2.  That will give you 5 additional inputs, the E, F, G and H inputs on PMDX-126 connector J11 and the K input on PMDX-126 connector J13.

Bob

[Techsavvy34]

Thanks for the help Bob.  I got it all sorted out.  The only way I could get it to work is power the sensors with the boards 12v and connect them individually to pins 11, 12, and 13.  I still had to use a resistor on each input otherwise the led on the board would be lit.

[EricColen]

As per my experience the LED in the proximity sensor is causing enough leakage current into the PMDX-126's inputs that the PMDX-126.
Also it has PNP sensors connected and that they are active.  If you have a volt meter or DMM handy, you can verify this by measuring the voltage between the "Pin11" screw terminal and the "GND" terminal.
 If you see a voltage somewhere around 9 volts or higher or higher with no metal present then that is the issue.  You can also look at the LED on the PMDX-126 next to the "Pin11" terminal. 

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