What is the convention for -Vs?
What is the convention for -Vs?
(OP)
I'm used to working with closed loop diagrams from college and during my research. However, in practice it is very common for the main lines from the output of an AC/DC power supply to continue from one page or sheet to the next. At the bottom and top of each line it is necessary to state the voltage so other people can follow the schematic. I know for -Vs there are technically several "truths." However, I'm curious what the standard practice or convention is when tagging Vs- (the negative voltage source potential or node; the wire connected directly to the negative terminal of the DC output).
From my perspective, simply saying DC GND makes the most sense for -Vs. However, you could say, for a 24Vdc power supply as an example, -24Vdc, as -24Vdc would be the potential with respect to +24Vdc (essentially flipping the leads of your multimeter in this case). Or you could even say 0Vdc, since -Vs in this case is your reference or ground potential (even though it may not actually be 0V with respect to real ground). But what is the most widely recognized practice?
I checked IEEE 315A among other standards but didn't find a clear answer. Does a standardized method for describing -Vs exist? Maybe "-Vs" is the answer? Please provide source(s) with your answer. Although I'd be interested to read your personal preferences, what I'd really prefer is an established method by an organization such as IEEE.
Thanks!
From my perspective, simply saying DC GND makes the most sense for -Vs. However, you could say, for a 24Vdc power supply as an example, -24Vdc, as -24Vdc would be the potential with respect to +24Vdc (essentially flipping the leads of your multimeter in this case). Or you could even say 0Vdc, since -Vs in this case is your reference or ground potential (even though it may not actually be 0V with respect to real ground). But what is the most widely recognized practice?
I checked IEEE 315A among other standards but didn't find a clear answer. Does a standardized method for describing -Vs exist? Maybe "-Vs" is the answer? Please provide source(s) with your answer. Although I'd be interested to read your personal preferences, what I'd really prefer is an established method by an organization such as IEEE.
Thanks!





RE: What is the convention for -Vs?
THAT IS A DEFINITE NO-NO. The voltages listed must be measurable relative to something that's designated as "ground."
Most systems would have the most negative node arbitarily designated as earth ground. The only time a -Vs would have a voltage level would be if there were both positive AND negative supplies, with ground in the middle somewhere, as in the case of most op amps. In fact, I would suggest that you crack open a copy of the "The Art of Electronics," which has gobs of circuit diagrams, or pop open a few op amp datasheets.
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: What is the convention for -Vs?
Power supplies are treated no differently.
RE: What is the convention for -Vs?
The company I work for is a military contractor but when they hired me they didn't have an EE working for them, so there are some bad habits I've noticed and have attempted to correct over the years (these "bad habits" were obviously never a danger to personnell or equipment, but rather mere inconsistencies and nonstandard approaches to commonly known standardized topics).
We use wire numbers on wire tags on our drawings to match the physical labels, as is the standard practice for any engineering or assembly company, which makes good sense especially for assembly and troubleshooting. However, for DC lines coming off the output the company has always simply used "0VDC TO LINE #####" or "0VDC FROM LINE #####" for -Vs. The purpose of my original post here was to determine if "0VDC" is correct based on an established standard and, if not, find some evidence to show a standardized alternative. I prefer to standardize everything I do, even when a specific standard is not required. This is better than choosing something merely because it's true and makes sense.
RE: What is the convention for -Vs?
I agree with VE1BLL that every wire should have a unique designation. The wires that are connected to DC negative in my world all have a designation ending in N while their counterparts on the other side of the battery all end in P.
RE: What is the convention for -Vs?
For this reason, what exactly a certain wire carries is often too complex to safely summarize. Thus the system wiring diagrams (system level) just "give up" giving hints - so to speak - and resort to using the universal solution I described previously.
Of course, many schematics (typically for a circuit card assembly) will use the usual ground symbol(s) and the floating T junctions (with label for voltage) for the common power supply rails. There's less risk with a PCB because you can't really incorrectly rewire it (internally) - e.g. cross wiring analog and digital grounds.
Every organization should have a drafting manual that refers to whatever obsolete and outdated standards they've failed to keep up with.
RE: What is the convention for -Vs?
I use the following when no other is required.
24VDC
24VRTN (as in 24V return) This avoids immediate comparisons to ground. and the confusion of using +24V and -24V I'm sometimes confronted with when the -24V is actually just 0V.
If both polarities are present:
+24VDC
24VRTN
-24VDC
Alternatively we use:
24VDC
0VDC
or
+24VDC
0VDC
-24VDC
Keith Cress
kcress - http://www.flaminsystems.com
RE: What is the convention for -Vs?
I like the Germans here. Siemens has been using the following system for decades. It is easy to use and understand and it doesn't need lots of special symbols - they even avoid their umlauts.
All positive voltages have a P.
The signal "ground" (grounded or not) is BS (Bezugsspannung i.e. Reference Potential).
The more common signal ground (and now, it is usually tied to GND) is M (for Masse or Mittelpunkt)
All negative voltages have an N.
Example:
+24 V P24
+15 V P15
+5 V P5
0 V BS
0 V M if grounded
-15 V N15
-24 V M24
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: What is the convention for -Vs?
Thanks again!