sink and source inputs Micro 830

[dhoyt1234 1]

Im working on my first allen bradley project so what Im asking is probably going to make you look at me funny put here it is... In any other controls products I have used ie johnson, alerton, invensys... inputs are usually setup to be able to accept dry contacts. In less Im doing something wrong that doesn't seem to be the case with this Micro 830 controller. I can jump COM0 to I-00 and nothing happens, the controller does not recognize this... The literature or anything I can find says the inputs are source / sink but nothing on how to setup either. In my experience with anything else a lot of times there is a jumper or dip switch to change whether or not you want to source or sink. I can not find anything that spells this out for this controller or what the default is. Seeing how I cant find any info I am here... What am I missing and what do I need to do? All I need is an input to recognize a momentary switch to initiate the logic... easy right?!! What do I need to do??

[Michael Lloyd 85]

I've never seen an input that doesn't require voltage of some kind. Doesn't mean that it doesn't happen, but even in the DCS world DI's need a voltage. Even sink/source needs voltage. I don't know anything about the 830 but if it's like all of the other AB products the DI card will be rated 24VDC / 120VAC / etc. Basically you power one side of the switch through a fuse, the other side of the switch goes to the DI point, and IN OUR SYSTEM, cards can be wired differently, the return (Neutral, ground, plus, whatever) is common on the card and wired to the appropriate point.

[dhoyt1234 1]

Right, I agree with that.. But how do I switch between source / sink? I don't have any voltage on my commons and I cant see anywhere to switch between sink and source?

[b_carlton 61]

How about just follow the wiring examples in the user manual? Don't guess.

[dhoyt1234 1]

Show me the wiring examples for the inputs and Ill gladly follow them... Maybe Im being dumb here but as far as I knew from my experience with other products source/sink means I either supply the voltage from another source or the voltage is supplied by the controller from its internal power... Am I wrong here? Im not about to try and put 24 volts to an input com and take the chance it smokes...

[Michael Lloyd 85]

Chapter 4, page 39

[Ken Roach 194]

Some controllers do provide the source voltage for their inputs, which you then can connect through 'dry contacts'. For example, this is common on controllers that are powered by 120VAC but have 24V DC inputs... they provide a 'Sensor Power' terminal. The 'COM' terminals on the Micro 800 series are not labeled with a polarity because the Inputs can be either Sinking or Sourcing depending on which polarity you wire to the Common terminal. Look carefully at the diagram for a Sinking input. The Negative side of the power supply is connected to the COM terminal, and +24 V DC is connected to the Input terminal. Now look at the diagram for the Sourcing input. If you want to use Sourcing inputs, you connect the Positive side of the power supply to the COM terminal, and 0V DC is connected to the Input terminal. As I understand them, you can use different COM terminal voltages for each group of inputs; Inputs 0,1,2,3 could be Sinking, while Inputs 4,5,6,7,8,9 could be Sourcing. There's a risk of confusion, sure, but there's also the flexibility to meet the needs of your application or your particular sensors. Edited 15 May 2013 by Ken Roach

[dhoyt1234 1]

Well I guess I am stupid because I still dont get it... So looking at this makes it seem like I need 24 vdc from some source no matter what and I either go 24 volts hot to common or to the input? I didnt go past high school guys I learned controls first hand through my company so forgive my ignorance, I barely passed my digital electronics class...

[Michael Lloyd 85]

No sir... no stupid people come to this forum. You have to have intelligence to ask for help. FWIW I'm self taught and still learning. And I went didn't go past high school either (but it was a GOOD high school lol) Ken posted above this with a good explanation

[dhoyt1234 1]

hahaha well thanks. Yeah this is a side project Im doing with a product my company doesnt use and we dont do process controls so working with AB has been a little different than what Im use to. Ken your explanation I think is what I was looking for... For my applications of simply a momentary switch, polarity has no affect and I can just wire 24 vdc common to my com terminal and wire 24 vdc hot through my switch and back to my input. The inputs are in no way internally sourced with the controllers power.

[HKU_MS 0]

You have it. you can use the DC source you are using to power the controler to power your inputs, the reason for having the inputs either sink or source is for transistor type input devices NPN will use sink and PNP will use source ("I think" sometimes I get confused on which way is which) I left high school early and went the technical school and ten years later to university then back to work in the trade so don't disparage yourself for lack of education, every project is an opertunity to learn something new that more than likely isn't in an university text book.

[dhoyt1234 1]

Thank you guys for the help!

[Guest]

well, if you've got it working don't let this confuse you – but if you're interested in knowing how a DC input can be made to function with EITHER a "sinking" OR a "sourcing" wiring configuration, the diagrams on page 39 of the user's manual tell the story ... basically the Opto-Isolator for each input has two LEDs inside it – not just one ... so one of the LEDs will always be able to light up (as highlighted in yellow) – and bias – or "fire" - the input's circuit (highlighted in green) into conduction ... . Edited 16 May 2013 by Ron Beaufort

[Ken Roach 194]

If you ever need a third career, Ron, clarifying RA manuals might be just the thing. Thanks for that illustration !

[Guest]

thank you for the kind compliment, Ken ... no, I'm not going to be looking for another career ... in fact, if I can find a buyer for the business, I'm thinking about retiring from my day job pretty soon ... hopefully the illustration will be helpful to someone further down the road ...