# Question regarding general schematic detail for transformers

Started by December 9, 2014
```Could some electronics guru please help ? Maybe this is a
very silly question, so pardon me.
In a schematic, a transformer is generally shown with 2 -3
parallel bars in the middle to indicate the core. Often, I
have seen the parallel bars replaced by a thick, solid bar.
So, do the parallel bars represent a laminated core
transformer and the thick single bar represent a ferrite
core transformer. Any hints, suggestions would be of help.
```
```On Tue, 09 Dec 2014 19:54:47 -0800, dakupoto wrote:

> question, so pardon me.
> In a schematic, a transformer is generally shown with 2 -3 parallel bars
> in the middle to indicate the core. Often, I have seen the parallel bars
> replaced by a thick, solid bar.
> So, do the parallel bars represent a laminated core transformer and the
> thick single bar represent a ferrite core transformer. Any hints,
> suggestions would be of help. Thanks in advance.

No such luck.  Someone out there may make such a distinction on their
schematics, but generally all the lines just mean a core of some sort.

--
www.wescottdesign.com
```
```On Wednesday, 10 December 2014 14:54:52 UTC+11, daku...@gmail.com  wrote:
> very silly question, so pardon me.
> In a schematic, a transformer is generally shown with 2 -3=20
> parallel bars in the middle to indicate the core. Often, I=20
> have seen the parallel bars replaced by a thick, solid bar.
> So, do the parallel bars represent a laminated core=20
> transformer and the thick single bar represent a ferrite=20
> core transformer. Any hints, suggestions would be of help.

It's not a distinction that's been used anywhere that I've worked.

Schematic symbols are arbitrary, like words in a language, and mean what th=
e majority understand them to mean. Three parallel lines isn't going to be =
confused with a connection (single line) or a capacitor (two lines). A sing=
le thick line is equally distinctive(if more tedious to create with a penci=
l or an pen). I doubt if there's anything more going on than that.

--=20
Bill Sloman, Sydney

```
```I was taught, solid lines mean laminated iron core, dashed means powdered
or ferrite.

Occasionally you'll see a single line, which might imply a smaller core
(or a lazy drafter).

A single line with an arrowhead means a variable reluctance coil (e.g.,
slug tuned).

Three lines might simply reinforce the concept of a laminated iron core
(proactive drafter?), or provide a symmetrical way to connect a grounding
wire to the core (common in sensitive applications, audio amps, test
equipment..).

Sensitive applications may also have shields, usually indicated as dashed
lines between a given winding, or set of windings, and the core.

There's also the uncommon tradition of a diagonal slash at each end:
.                   /
.   /--------------/
.  /--------------/
. /
to indicate a square loop (magnetic amplifier type) core.

Tim

--
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com

<dakupoto@gmail.com> wrote in message
> very silly question, so pardon me.
> In a schematic, a transformer is generally shown with 2 -3
> parallel bars in the middle to indicate the core. Often, I
> have seen the parallel bars replaced by a thick, solid bar.
> So, do the parallel bars represent a laminated core
> transformer and the thick single bar represent a ferrite
> core transformer. Any hints, suggestions would be of help.

```
```On Tue, 09 Dec 2014 23:40:17 -0700, Tim Williams
<tiwill@seventransistorlabs.com> wrote:

> I was taught, solid lines mean laminated iron core, dashed means powdered
> or ferrite.
>
> Occasionally you'll see a single line, which might imply a smaller core
> (or a lazy drafter).
>
> A single line with an arrowhead means a variable reluctance coil (e.g.,
> slug tuned).
>
> Three lines might simply reinforce the concept of a laminated iron core
> (proactive drafter?), or provide a symmetrical way to connect a grounding
> wire to the core (common in sensitive applications, audio amps, test
> equipment..).
>
> Sensitive applications may also have shields, usually indicated as dashed
> lines between a given winding, or set of windings, and the core.
>
> There's also the uncommon tradition of a diagonal slash at each end:
> .                   /
> .   /--------------/
> .  /--------------/
> . /
> to indicate a square loop (magnetic amplifier type) core.
>
> Tim
>

EE's knew what you meant, but the OP is not a EE, so should probably
expand that to

"...indicate a square hysteresis core..." [shich actually means a core
WITH square hysteresis characteristics] and then add, where the core has
almost no linear range of operation, it is either fully saturated one way
or the other. Such cores are used in circuitry called 'magnetic amplifiers'
```
```On Tue, 9 Dec 2014 19:54:47 -0800 (PST), dakupoto@gmail.com wrote:

>very silly question, so pardon me.
>In a schematic, a transformer is generally shown with 2 -3
>parallel bars in the middle to indicate the core. Often, I
>have seen the parallel bars replaced by a thick, solid bar.
>So, do the parallel bars represent a laminated core
>transformer and the thick single bar represent a ferrite
>core transformer. Any hints, suggestions would be of help.

Now that people use CAD and don't draw on paper, the tendency is to
use the standard CAD package symbol for an inductor or a transformer.
So all Ls look the same, and all two-winding Ts look the same.

Our transformers and inductors each have two bars to suggest a core...
even if there's no core. There are really no rules for this sort of
thing.

In LT Spice, inductors are squigglies with no bars. A transformer is
any two or more inductors, anywhere, that are associated by a "K"
command, itself anywhere on the screen.

Note that L denotes an inductor and T a transformer. Is's annoying
when amateurs make up things like IC3 and FET7 and RLY2. There *are*
rules for reference designators.

--

John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

```
```Tim Williams wrote:
> I was taught, solid lines mean laminated iron core, dashed means powdered
> or ferrite.
>
> Occasionally you'll see a single line, which might imply a smaller core
> (or a lazy drafter).
>
> A single line with an arrowhead means a variable reluctance coil (e.g.,
> slug tuned).
>
> Three lines might simply reinforce the concept of a laminated iron core
> (proactive drafter?), or provide a symmetrical way to connect a grounding
> wire to the core (common in sensitive applications, audio amps, test
> equipment..).
>
> Sensitive applications may also have shields, usually indicated as dashed
> lines between a given winding, or set of windings, and the core.
>
> There's also the uncommon tradition of a diagonal slash at each end:
> .                   /
> .   /--------------/
> .  /--------------/
> . /
> to indicate a square loop (magnetic amplifier type) core.
>
> Tim
>
That is the way I have seen schematics; the drawing showing /
indicating nature of the core.

```
```On Wednesday, December 10, 2014 4:07:08 PM UTC, John Larkin wrote:
> On Tue, 9 Dec 2014 19:54:47 -0800 (PST), dakupoto@gmail.com wrote:
>
> >very silly question, so pardon me.
> >In a schematic, a transformer is generally shown with 2 -3
> >parallel bars in the middle to indicate the core. Often, I
> >have seen the parallel bars replaced by a thick, solid bar.
> >So, do the parallel bars represent a laminated core
> >transformer and the thick single bar represent a ferrite
> >core transformer. Any hints, suggestions would be of help.
>
> Now that people use CAD and don't draw on paper, the tendency is to
> use the standard CAD package symbol for an inductor or a transformer.
> So all Ls look the same, and all two-winding Ts look the same.
>
> Our transformers and inductors each have two bars to suggest a core...
> even if there's no core. There are really no rules for this sort of
> thing.
>
> In LT Spice, inductors are squigglies with no bars. A transformer is
> any two or more inductors, anywhere, that are associated by a "K"
> command, itself anywhere on the screen.
>
> Note that L denotes an inductor and T a transformer. Is's annoying
> when amateurs make up things like IC3 and FET7 and RLY2. There *are*
> rules for reference designators.

Rules that many engineers don't follow.

NT
```
```On 12/10/2014 9:07 AM, John Larkin wrote:

> Note that L denotes an inductor and T a transformer. Is's annoying
> when amateurs make up things like IC3 and FET7 and RLY2. There *are*
> rules for reference designators.

There are *conventions*, not "rules".  (Where are the Designator Police?)

```
```On Wed, 10 Dec 2014 14:01:47 -0700, Don Y <this@is.not.me.com> wrote:

>On 12/10/2014 9:07 AM, John Larkin wrote:
>
>> Note that L denotes an inductor and T a transformer. Is's annoying
>> when amateurs make up things like IC3 and FET7 and RLY2. There *are*
>> rules for reference designators.
>
>There are *conventions*, not "rules".  (Where are the Designator Police?)

There are MIL and ANSI specs for reference designators.

My only break from the rules is to use D (not CR) for diodes. I don't
use many dynamotors on my boards these days.

Things like CON4 and TR3 and RN5 and POT2 look dumb. But everyone is
free to look dumb if they want to.

--

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

```