ABM Current Source - Current Direction is Opposite

[m3nth]

If I use a regular DC Current source of 1A, and an ABM Current source with just 1 for the value (ie, 1A), the direction of current coming out of the ABM source is opposite that of the DC Current source, and in the opposite direction of the arrow on the ABM Current Source icon.  This polarity reversal requires a negative sign to fix and is confusing... is there a reason for this or is it just a bug?  I didn't find anything noted on this peculiarity under the help files for the ABM source.

[lacy]

In my tests that I have performed I would have to say that the ABM Source is the one with the correct markings. Current flows in the direction of the arrow with it. The DC Current source on the otherhand is the one marked backward in my opinion

I will post both Test Circuit for you to examine.

[lacy]

I don't want to confuse you but I have a theory on why the DC Current source arrow points in the wrong direction. In the old days current was to believed to flow from positive to negative. This was know as conventional current theory. What we use now is known as the electron current theory and this theory has current or electron flow from negative to positive.

Now I don't know if this was just an error when they created the symbol or they made it that way as a throw back to the old days of conventional current. I think if the latter was the case, then it should be updated to modern conventions and the arrow in line with current flow as we know it today.

This is just my hypothesis since I can't climb into the minds of the software developers.

[m3nth]

Lacy, what is your background?  Conventional current flow is the notation used today in practically all electronics and is defined (like you said) as the flow of positive charge.  The flow of positive charge into a passive device (ie, resistor) creates a positive voltage on the input pin of that device.  The flow of positive charge into the positive terminal of an ammeter creates a positive reading on the ammeter.  This is how all modern instruments and electronics are designated, as well as being the convention used by Multisim, with the apparent exception of the ABM source.

[lacy]

My background is in Industrial Electronic Servicing with over 20 years experience analyzing electrical and electronic circuits. I have to disagree with what you are saying. What we know now is called the Electron Current Theory and it is electrons (current) flowing from a negative potential to a postive potential. Way back in history they believed that current flowed from the postive potential to the negative potential. This called Convential Current Theory and is backward from what we recognize today. What you are describing is what I would refer to as "hole theory" where postive charged "holes" travel from the positive potential to the negative potentional. This still would have electrons flowing from negative potential to the positive potential. This is mainly taught to explain the operation of PNP and other P-type components.

With all that said,  Multism follows the only accepted theory of Electron Current Flow where electrons flow form negative or ground to postive.or +12V.

I don't know if conventional theory is even being taught in colleges anymore since the Electron Theory is consider the norm. I was taught using the Electron Theory but I did have to learn the other theory and if you have ever used the right-hand-rule for coils then you are using the conventional current theory.

Here's a link that you might find interesting.

http://www.newton.dep.anl.gov/askasci/phy00/phy00628.htm

[lacy]

Her's a great link that probably explains what I am refering to better that what I can explain it.

Anyway, the DC Current Source's symbol is still the one that is backward when using Electron Theory and the ABM is correctly labeled. If you are using the conventional theory, then the oposite is true. It depends on your perpesctive based upon which convention you are trained to use or are comfortable with.

In my opinion, they just messed up when creating the symbols. They need to correct one of them and I really don't care which one, because whether you use conventional or electron theory it would be easy to figure it out which way the current is going depending upon which convention you choose to use. In my opinion, I would change the ABM, since I think everyone is already familiar with arrows being the opposite actual electron flow and would satisfy the users of both theories.

http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

Message Edited by lacy on 10-07-2007 06:30 PM

[digitalguy]

Hi all,

I am a professor at a college here in So. Cal. teaching in the Engineering Division. I state this only to give you some background as to where I'm coming from. In Electrical Engineering it is common to use conventional current flow. You will be hard pressed to find an engineering level text book that does not use conventional current flow. Even many technician level texts use conventional current flow (Boylested and Bogart, for example). I would be very surprised if Multisim did not use conventional current flow. In analysis, it makes absolutely no difference which convention you use as long as you are consistent. I believe the gentleman has a point as to the direction the arrow points on the ABM current sourse as I don't believe Multisim would "go against convention".

[lacy]

http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

This link will explain my point of view better that what I can. I was trained in the electron flow theory and conventional flow theory. I find the electron theory is easier for me to follow. Most devices symbols have arrows point in the opposite directon of electron flow. So using conventional theory the ABM would be considered labeled backward and the DC Current source correct. But using the electron theory the opposite is true.

It's all a matter of perspective and which theory you are most comfortable with. I agree that they need to change the symbols. I would change the ABM since like you said since most devices symbols follow the conventional current labeling ( I.e symbol for an NPN transitor has the arrow opposite actual current flow). But, Multism considers current flow from negative to postive when taking measurements even though the components are labeled using the conventional method.

[lacy]

As far as my last comment in the previous post that could also be a matter of perspective also. In my perspective, current measurements or voltage measurements are from negative to postive I thought I would clarify that a bit.

You guys correct about the notation aspect and I think we have come to agreement on that even though our perspectives on current flow are totally opposite. I was looking at current/electron flow and not thinking about the symbol as it is generally accepted.

I have always wondered about engineers and I guess I have finally figured it out. You design things backward and that is why there is need for Technicians to straighten things out. (This is a Joke of course so don't take offense)

Message Edited by lacy on 10-07-2007 08:09 PM

[lacy]

One other thing and i will let this discussion end. You say you have to input a negative value into the ABM in order to make it correct. Instead of doing that, why not flip it vetically and leave the value as postive? It still isn't going to look right to you on the print, but it would satisfy your method of circut design/analysis until it can be corrected. Just a thought. You can do it however you want that makes it more simpler for you.