Help in 2-wire sourcing input

I don't want an explanation of sinking and sourcing. I would just like to know if a SMC D-A73H reed switch has only 2 wires (a -blue one and a +brown one in our mitsubishi plc's). How would I wire it to a 1747-L20E with sourcing inputs. I want to use the PLC provided 24VDC if possible.
Thanks Steve

Very easy connect the brown to Your power supply to the +
connect the blue to your input.
make sure that your PLC common inputs get the -.
you are connecting in PNP.
Your read switch will work any how but if you swap between the blue and the brown the led will not light.

Thanks
I will connect the brown to 24VDC out and the blue to the input.
" make sure that your PLC common inputs get the -.
you are connecting in PNP"
This is where I seem to get lost. If I have only 2 wires how do I connect in PNP? If my brown wire is on 24VDC and the blue is an input, what is meant by PLC common getting the -? With a 2 wire switch, didn't I put it on the input?
Thanks Steve

Maybe I am just overcomplicating this. I just don't get the pictures on page 144 of this http://www.ab.com/manuals/cp/1747621.pdf this shows the use of 2 and 3 wire switches. Only the 3 wire can use 24VDC out? Can't I wire the brown to the 24VDC OUT and the blue to the input? Or does the use of a 2 wired switch force external 24VDC power source? Is this what is meant by connecting the - to PLC common? If so then I can;t be using the PLC 24VDC OUT for sensor power correct?
Steve

Go to AB website and download manual. Wiring is in
Chapter5...
http://www.ab.com/manuals/cp/1747621.pdf

Thanks I did that. I just can't seem to make out the PLC 24VDC connection in relation to a 2 wired switch. It looks to me as though the use of this type sensor is forcing the use of an external power supply with it's - connected to PLC COM and the sensors connected to Power supply 24VDC. The + wire break between inputs 3 and 5 don't carry over from the 24VDC OUT of PLC. The 2 and 3 wire inputs from input 5 and above are getting it from an external source. That's how it looks to me for all PLC in this family. Have you looked at the pictures in appendix E specifically page 144?
Steve

scandle,
Notice note 1 on the PWR OUT +24VDC, it says 200ma user power available. I think the diagram is just showing you that you can use the internal power supply, but if you exceed the 200ma range then you need to use the external +24VDC. The break in the wire between input 3 and 5 is showing you just that.
Tim

It is a REED SWITCH !

It's the same as a push button except it is magnetically activated.

It is activated by the magnet in the cylinder instead of a finger.

Which-color-where doesn't matter.

Put either wire to the Sourcing input and the other to the common - done.

Not exactly, Terry.

The reed switch will work at any polarity, that's right.

However, that nice little red or amber LED that indicates the switch state will not... Those baby lights come handy sometimes, aren't they?

Therefore, if having the light working is a desirable thing, the brown wire should go to +24 VDC and the blue one - to the input.

(scandle called this thing "sourcing", which is absolutely correct throughout the English-speaking world - except, of course, The Most Preeminent Allen-Bradley... They call it "sinking")

Sorry, ArikBV - you have already explained that and I missed it...

LadderLogic said:

However, that nice little red or amber LED that indicates the switch state will not... Those baby lights come handy sometimes, aren't they?

Therefore, if having the light working is a desirable thing, the brown wire should go to +24 VDC and the blue one - to the input.

Click to expand...

In all the 'confusion', that little LED may have bit the dust during scandle's wiring lesson.

There's an even better chance that the reed switch is gone. Ask them to pass more than their rated current (like when you connect them ACROSS a supply!), and they'll turn on ONCE, welding the contacts, never to turn off again...

beerchug

-Eric

Fine!

Try it one way... then try the other.

Terry and Ladderlogic you are both right

Yes it is a reed switch and will turn on when the magnet on the cylinder piston is in position, and it wont matter witch way it is wired. But if you want to adjust it to get the correct position it sure helps to have it wired correctely so the LED works

So just point the brown wire towards to positive and the blue towards negitive and all will be OK.

Dave Newey
Technical support
SMC Pneumatics Melbourne Australia

Thanks, Dave.

BTW, some pneumatics manufacturers (don't know if SMC is among them) use Hall switches instead of reeds. For those, polarity does matter in both senses...

WOW I wanted to thank everyone and hope I didn't seem like a newb but I did try to hook it up as everyone stated and no change in input state. I tried another one (brand new) and same result-no change in input state.

"There's an even better chance that the reed switch is gone. Ask them to pass more than their rated current (like when you connect them ACROSS a supply!), and they'll turn on ONCE, welding the contacts, never to turn off again... "

http://www.flo-products.com/floprod/smcaut03.html#2

"(scandle called this thing "sourcing", which is absolutely correct throughout the English-speaking world - except, of course, The Most Preeminent Allen-Bradley... They call it "sinking")"

I would not refer to inputs as sinking or sourcing myself. Allen Bradley refered to it as sourcing input device on page 144.
http://www.ab.com/manuals/cp/1747621.pdf


I have fabricated a few machines and installed Allen Bradley's in the past. When I hooked this switch and it didn't work I started to read the manual. That is when I got lost. Everything appeared to be correct to me. Chapter 5 describes sinking and sourcing devices but in all examples show a 3 wired switch. The appendix page 144 shows 2 and 3 wire configurations but 2 wire switches/contacts are utilizing an external power source. I ASSumed this was due to the fact that a switch using PLC 24VDC OUT to the brown wire and the blue wire on the sinking input, that when the piston magnet closed the switch the input would come on. It didn't and my only thought is the VDC COM and the input terminal are not at the same potential with respect to the 24 VDC OUT. Now if I attach an external power supply and wire the -/common to the VDC COM and the brown to + and blue to input there is a potential difference and it should function. Correct? However if I just hook the 24VDC OUT to the brown wire and put the blue on the input, won't I also have to attach the input to the common also or is this done internally? Am I just way off base here?

One last bit here. The Allen Bradley shows the input circuitry on page 145 for the 1747-L20E plc. The sinking input diodes are not in the direction SMC shows for there reed switch on page 5.3-7 of this manual for PLC connection and sink inputs. http://eul0600038.eu.verio.net/MultiSite/MultiSite/SharedObj/EBP/VOL2/Volumen2(UK)/Serial2(UK)/Related/DSeries_(UK_).pdf

This horse is almost dead!!!
Steve