Negative vs Positive DC Inputs

[TxPowerEE]

I have tried to explain DC negative vs positive inputs to a bunch of sales guys. Let's just say I have not been very succesful. Does anyone know of a site that has some elementary information that I can send them to or some info I could use to help get this across.

 

[itsmoked]

Sorry but you are still being unsuccessful..

This appears so totally obvious and transparent, (like 4th grade science), that we are not going to be able to help you without more input.

Please try with us again. What is this all for? Maybe that will help us - help you.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

I have explained that to my five year grandson. I used a battery and a motor. Switching poles reversed the motor. He could read the plus and minus sign on the battery and he saw the motor running in opposite directions when changing poles. That's all he needed to know and I don't think your sales guys need to know more either.

Keep it simple...



Gunnar Englund

http://www.gke.org

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

 

[TxPowerEE]

The actual application is PLC input cards, where a 3rd party's output is negative and our input cards are positive with power being drawing from 24VDC batteries. I have tried back of the napkin drawings to only get deer in the headlights looks.

I was hoping someone knew of some material or site that had information I could send them to. I know its simple but instruction was never my strong point.

 

[xnuke]

The problem could be your terminology. Try searching "sinking vs sourcing" on your favorite search engine. You'll find a ton of information, but be aware some manufacturers define the terms differently since some are discussing from the field device point of view and others are discussing from the PLC point of view. I know some people who happen to like AutomationDirect's explanation at:

http://www.automationdirect.com/static/specs/sinksource.pdf

The diagrams are pretty clear.

Others like:

http://www.patchn.com/npnpnp.htm.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[TxPowerEE]

Pictures! Better than I could draw. Thanks Xnuke. Great tip on the search positive vs negative inputs turns up nothing very useful on google.

 

[controlsdude]

I thought the Japanese honda automotive were big on neg dc where they grounded the positive side and used the dc common to power.

Then you had to use sinking inputs. The result of this was that if you ever troubleshoot an input that is triggered by providing a common through the card. It is very hard to troubleshoot since your looking for a dc common.

Most plc manufacturers do not provide off the shelf sinking cards. Usually its a long lead time.

 

[roydm]

Controlsdude - British cars too used Positive ground for many years, I think they made the switch when Alternators replaced generators but don't quote me.
It's not just as simple as sinking vs sourcing, occasionally you get an output that goes negative in relation to ground e.g. 0 = 0V, 1 = -12V

Sales guys eyes glaze over, if ever you try to talk about something they don't sell, they just want to move their product, they don't really care about your problems.
Roy