LG LS PLC proximity inputs, PNP or NPN? 1

[PeterLG]

I have been given the task to buy an LG PLC (K120s)20 to 40 I/O, I need to input some proximity switches, do I use PNP or NPN, I want to use the inbuilt 200ma 24v power supply, I'm getting old and have forgotten all I knew about transistors as I haven't done a lot with them, I can plod my way thru writing a ladder program for it but not sure on the inputs.
Input specification
On voltage/current DC19V or higher/5.7mA or higher
Off voltage/current DC6V or lower/1.8mA or lower
Input impedance About 3.3?
I want to use the inbuilt 24v power supply negative to common on inputs for stop start push buttons, but not sure which proximity's to buy?
Thanks in advance

http://eng.lsis.biz/product/product...fer_product=third_down_view.asp&catlev3_id=13

 

[Skogsgurra]

That PLC has active high inputs. So you should use PNP outputs from the proximity switches.
It also means that you shall connect push button common to +24 V. Negative won't work. All inputs need "sourcing" signals, i.e. signals that go high when active.
Using the internal +24 V is good. But you will have to consider total load. If the inputs draw 5.7 mA at 19 V, they will probably draw just above 7 mA at 24 V. Check if your total load is within the 200 mA of the unit.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[PeterLG]

Thanks for that, I expected the PNP would be the go, but the brain has faded too much over the years............., I haven't purchased anything yet.
This is the sensor I am trying to use, it is NPN

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=260442027793

However I have searched and found this info on the PLC, whoops, I will have to shut down and add another post to finish this one..........

 

[PeterLG]

I have searched online and found a manual for this controller here

http://www.gavazzionline.com/pdf/K120UserManual.pdf

and on page 75 of the pdf is says this
3) Input wiring
Main unit’s wiring method is as follows. DC input specifications offered by MASTER-K120S is to be used for both electric current sink and electric current source.
It also shows the inputs broken up into 2 banks, I wonder if I can SOURCE one lot for push buttons and sink the other lot for NPN proxys?

 

[Skogsgurra]

As you can see in pictures on page 6-2, there are two diodes in the optocouplers. That means that current can flow into or out of the terminals and you will have the input activated either way. Some manufaturers use a diode bridge for that purpose, but these guys are a bit smarter.

So, you are free to use almost any configuration you choose. But, I would prefer to use the standard configuration with PNP and sourcing switches for all inputs. That gives you a fail-safe function and much less confusion. Same rule applies to all input. Makes life easier.

There are PNP devices available from the vendor you referred to.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[PeterLG]

Thankyou for enlightening me, I would prefer to have all inputs the same way as well, I suppose I could use NPN's and positive common to the push buttons, I would prefer the other way though. I have searched the vendors store for "PNP" & "Proximity" separately, and can't find any PNP proxys from him. The reason I picked these is the sensing distance and the price, the price is a key thing to project going ahead.