AoE x-Chapters - 1x.1 Wire-&-Connectors

[David Nadlinger]

On 06.08.19 11:28 PM, Phil Hobbs wrote:
> I'd never write "litz wire" with a capital.

Oh, sure.

But said circled-capital-L footnote in the text is about referring to
the German word rather than the English loanword. You'd still say that
the word "litz wire" comes from "Litzendraht", not "litzendraht".

That's all I was trying to point out – but as the editors will catch
that anyway, back to electronics design, shall we?

— David

 

[Phil Hobbs]

On 8/6/19 9:08 PM, Sjouke Burry wrote:

On 07.08.19 0:24, Phil Hobbs wrote:
On 8/6/19 2:43 PM, Tim Williams wrote:
"Jan Panteltje" <pNaOnStPeAlMtje@yahoo.com> wrote in message
news:qicbcm$ckr$1@dont-email.me...
I just wished people would no longer use filenames like
ThisSchematicIsTheLatestAndGreatest.PDF
3x.20_Precision-1.5kV-1us-Ramp_WH.pdf


My favorite is the,

Customer Project 12345_dingleBerryPOWERSUPPLY_REV_E.SCH

A true blend of DOS-style ALLCAPS (but still using LFNs?),
caps-avoidance, underscores (when a space apparently isn't available?)
AND spaces (oh..).

Working with other people has only reinforced my understanding that the
90-10 rule applies no matter how "educated" a group you're sampling...

Tim


I use camel case e.g. because it helps a lot finding the right file from
my archives, e.g.

2019-08-05-InvoiceABC05.pdf
TLV431AshuntRefOnSemiUnstableHorribleAvoidAvoid.pdf

Cheers

Phil Hobbs

Camel case programmers should be removed from this earth.......

You probably use tabs instead of spaces too. Blech.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[George Herold]

On Tuesday, August 6, 2019 at 3:29:22 PM UTC-4, John Larkin wrote:

On Tue, 6 Aug 2019 10:15:59 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Tuesday, August 6, 2019 at 12:32:07 PM UTC-4, John Larkin wrote:
On Tue, 6 Aug 2019 07:34:26 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Tuesday, August 6, 2019 at 10:16:04 AM UTC-4, John Larkin wrote:
On Tue, 6 Aug 2019 00:32:26 -0500, "Tim Williams"
tiwill@seventransistorlabs.com> wrote:

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:cavhkeppudjiempknhs0jb84jpkau3sgo8@4ax.com...
Signal integrity is easy. PCB layer 2 is solid ground plane. Bolt it,
and grounded connector shells, to the metal box in as many places as
possible.

Cable shields to the box ditto.


Not really. Suppose there's a huge noisy inverter in the box. Ground loop
currents once again. Cables simply tied "shields to the box", and PCB
"bolt[ed] ... to the metal box", draws those currents into both. Now your
precision ADCs are all reading trash.

Here's a 12-bit, 250 MHz ADC a couple inches from a multi-output
switching power supply. The 6-diode CW multiplier string is about an
inch away.

https://www.dropbox.com/s/opa02hou39tduiq/ESM_rev_B.jpg?raw=1

Noise is below 1 lsb RMS.

One solid layer 2 plane. Everything is grounded.

Sure, but star grounding has a place at low frequency.
I cut my star grounding 'teeth' making a low freq. teaching lockin.
https://www.teachspin.com/signal-processor-lock-in

Where a uV of 'signal' getting into the wrong input would ruin my whole day.

George H.

The way to avoid ground loop errors is to keep signals differential.
Hmm, OK I guess that would help... In the end thinking is required.
I think most of the time I have ground issues, I don't think about it
enough ahead of time. Or maybe you just have to bump your head into a
ground problem before you know enough to think about it. And then it's a circuit
redesign or adding a crutch* to the instrument.

George H.
*I'm thinking of this piece of plastic I had to add to our diodle laser controller
to isolate the DB9 connector shell from the back panel ground.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

I most always bolt the connector shell to the box, and also solder it
to the main PCB ground plane. You never know what nasty stuff might
come in over the shield. Best to stop it soon.

Right, me too. In this case the cable carried laser current and
TEC current...(I think, it might have been the HV piezo voltage?)
They all had two leads, but for electrostatic reasons the laser
diode case is part of local ground on the laser head...
TBH I can't recall the details, everything worked till the DB9
connector was hooked up to the back panel... and when we did that
some low level crud/ interference. Maybe the difference between the
front and back panels with various screws and pieces in the box?
There's a wire that connects the DB9 shell to the power supply/
front panel ground.

VME is an exception. Dsub shells are bolted to the module front panel
(rack ground) but not connected to the PCB/VME ground plane. Caps are
OK.

Yeah I'm mostly an idiot, when hooking up ground...
(I only think about it when it doesn't work quite right.)

Grounding everywhere you can..with attention to any
connectors, can totally work*.

One thing that I've never seen discussed much is that if
you've got a shielded box / probe thing, then (above
some frequency.. skin depth?) the outside ground and
inside ground can be different. At least that's how I
think about it.

George H.

*we put a 10 k ohm $0.02 TH metal film resistor, down the bottom
of a LN2 probe to measure noise vs temperature.
And sell it for more than $0.02. (last time I measured,
the change in resistance between 300K and 77K it was about 1%
for cheap MF resistors.. for teaching students it might be
better if it changed more. (there are phoenix terminal
blocks in the probe so people can add whatever R's the want.)

 

[Sjouke Burry]

On 07.08.19 0:24, Phil Hobbs wrote:

On 8/6/19 2:43 PM, Tim Williams wrote:
"Jan Panteltje" <pNaOnStPeAlMtje@yahoo.com> wrote in message
news:qicbcm$ckr$1@dont-email.me...
I just wished people would no longer use filenames like
ThisSchematicIsTheLatestAndGreatest.PDF
3x.20_Precision-1.5kV-1us-Ramp_WH.pdf


My favorite is the,

Customer Project 12345_dingleBerryPOWERSUPPLY_REV_E.SCH

A true blend of DOS-style ALLCAPS (but still using LFNs?),
caps-avoidance, underscores (when a space apparently isn't available?)
AND spaces (oh..).

Working with other people has only reinforced my understanding that the
90-10 rule applies no matter how "educated" a group you're sampling...

Tim


I use camel case e.g. because it helps a lot finding the right file from
my archives, e.g.

2019-08-05-InvoiceABC05.pdf
TLV431AshuntRefOnSemiUnstableHorribleAvoidAvoid.pdf

Cheers

Phil Hobbs

Camel case programmers should be removed from this earth.......

 

On Monday, 5 August 2019 15:20:18 UTC+1, Winfield Hill wrote:

Here's a DRAFT copy of x-Chapter 1x.1, which starts
things off, by dealing with wire and connectors.
Comments and corrections please.

https://www.dropbox.com/s/kz335xwvl5v8gie/1x.1_Wire-%26-Connectors_DRAFT.pdf?dl=1

Stranded wire: no mention of extra-flex or the main reason unstranded is used: lower cost.


NT

 

[Phil Hobbs]

On 8/6/19 10:02 AM, George Herold wrote:

On Monday, August 5, 2019 at 9:58:20 PM UTC-4, Phil Hobbs wrote:
On 8/5/19 8:50 PM, George Herold wrote:
On Monday, August 5, 2019 at 2:23:12 PM UTC-4, Phil Hobbs wrote:
On 8/5/19 8:32 AM, Winfield Hill wrote:
Here's a DRAFT copy of x-Chapter 1x.1, which starts things off, by
dealing with wire and connectors. Comments and corrections please.

https://www.dropbox.com/s/kz335xwvl5v8gie/1x.1_Wire-%26-Connectors_DRAFT.pdf?dl=1




Wow, an embarrassment of riches today.

One other thing about Teflon wire is that it's a royal pain to strip
using dikes.
Huh, Phil, I've been meaning to ask this for a while... but it
seems to me you need a good pair of dikes, with sharp holes for each
wire size. I've got these "paladin" strippers.. but I think someone
bought them out.
Can I send you some good strippers for your Birthday? :^)

I'll be 60 late next month, so a few strippers would be apropos--just
don't tell my wife. Maybe they could jump out of a cake.

I generally use Xcelite flush cutters, which are far better than the
usual axe-blade dikes. I also have the usual spade lug crimper / bolt
cutter/ wire stripper tools. I don't like the big clunky strippers that
mechanically sense the insulation and adjust their blades accordingly--I
just want insulation to do as it's damn well told, and Teflon doesn't,
in so many, many ways.

Well I've got a pair of these,
https://www.amazon.com/Greenlee-PA1118-GripP-Stripper-Cutter/dp/B0006BHHDQ
(I guess Grennlee bought Paladin tools) If you don't have something like that
then that's what's coming for your B-day. I see Amazon has a deal on two pairs,
(different wire sizes.) I don't think I can make 'em jump out of a cake. :^)

George h.

Very kind of you, but I'd never use them. (The ones that come out of
the cake though...nah, I'd never use those either.)

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

On Wednesday, 7 August 2019 02:42:40 UTC+1, tabby wrote:

On Monday, 5 August 2019 15:20:18 UTC+1, Winfield Hill wrote:
Here's a DRAFT copy of x-Chapter 1x.1, which starts
things off, by dealing with wire and connectors.
Comments and corrections please.

https://www.dropbox.com/s/kz335xwvl5v8gie/1x.1_Wire-%26-Connectors_DRAFT.pdf?dl=1

Stranded wire: no mention of extra-flex or the main reason unstranded is used: lower cost.


NT

also tinsel wire.
PVC is frequently rejected due to its vulnerability to chemicals as well as heat
Magnet wire comes in various temperature/lifetime grades, single & double coated, solderable and gotta-scrape. And colours.
Higher temp insulations: glass fibre, ceramic beads. Asbestos historically.

Lots of domestic kit has been made on ss & ds boards. They haven't disappeared.
FR-4... FR2 is still popular for domestic grade goods. Some use other variants too.
Robot stuffing? Masses of stuff is hand soldered in the 3rd world.
If the soldering scorches anything, it went wrong. Soldering temp profiles.
What's strange about ounces per sqft?

"If there’s more than one wire, you call it a cable."
or flex if stranded, short for flexible cable.
Multicore.

"flows through a conductor, the current is not uniform throughout the bulk – it is concen-trated in an outer layer "
sometimes


NT

 

[Phil Hobbs]

On 8/6/19 10:44 AM, Don Kuenz wrote:

boB <boB@k7iq.com> wrote:
On 5 Aug 2019 05:32:08 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

Here's a DRAFT copy of x-Chapter 1x.1, which starts
things off, by dealing with wire and connectors.
Comments and corrections please.

https://www.dropbox.com/s/kz335xwvl5v8gie/1x.1_Wire-%26-Connectors_DRAFT.pdf?dl=1



Did you notice the one note in this version ?

"Paul, litzendraht, and litz, all need to be lower case."


Also, since you have some handy tools in the chapter, one useful tool
that we use often is the electric enamled wire stripping tool of which
there are a few out there... Might be worth a picture...

https://www.ebay.com/itm/Pro-DF-6-handheld-Magnet-wire-Stripping-Machine-stripper-Cutter-110v-US-STOCK-/333086834927


https://www.aliexpress.com/item/32749284319.html

https://sanshinetechnology.en.made-in-china.com/product/EKTnzLDCuQcp/China-Handset-Enamel-Wire-Stripping-Machine-SS-SM06-Repalce-ABISOFIX-Stripper-.html

A stripping machine sure seems better for my own health than dipping one
end into a solder pot (IIRC) or a jar of paint remover.

The vapour pressure of lead at soldering temperatures is very low. So
solder pots are pretty safe as long as you don't tip it over on yourself.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

On Wednesday, 7 August 2019 03:42:29 UTC+1, Phil Hobbs wrote:

On 8/6/19 10:44 AM, Don Kuenz wrote:

A stripping machine sure seems better for my own health than dipping one
end into a solder pot (IIRC) or a jar of paint remover.

The vapour pressure of lead at soldering temperatures is very low. So
solder pots are pretty safe as long as you don't tip it over on yourself.

Or nearly fall over & stick your hand in it. Or not pay attention for a moment & in it goes. I don't mind using them but don't regard them as safe.


NT

 

[John Larkin]

On Tue, 06 Aug 2019 22:57:42 +0300, upsidedown@downunder.com wrote:

On Tue, 6 Aug 2019 08:41:09 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 6. august 2019 kl. 17.06.48 UTC+2 skrev Don Kuenz:
Tim Williams <tiwill@seventransistorlabs.com> wrote:
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:cavhkeppudjiempknhs0jb84jpkau3sgo8@4ax.com...
Signal integrity is easy. PCB layer 2 is solid ground plane. Bolt it,
and grounded connector shells, to the metal box in as many places as
possible.

Cable shields to the box ditto.


Not really. Suppose there's a huge noisy inverter in the box. Ground loop
currents once again. Cables simply tied "shields to the box", and PCB
"bolt[ed] ... to the metal box", draws those currents into both. Now your
precision ADCs are all reading trash.

But with visibility to where the currents are flowing, or with a
star-grounding scheme, those loop currents stay separate. Say the
connectors are clustered on a front panel, shields grounded to it. That
keeps outside noise out, good. Collect the interior cables (which are still
all grounded to the same point, preferably as coaxially as possible, no
weedy wire links), and bundle them into a single harness. Ferrite beads as
needed. They go over to the PCB, which no longer needs chassis ground at
all.

Or do the brute-force method and use welded chassis compartments to keep the
bignasty away from the quietstuff. Cost doesn't much matter in your test
equipment, but it's a very real tradeoff in production. Production even
likes to avoid metal if they can...

My recent audio mix-amp project motivated me to read, or at least skim,
dozens of articles about /audio/ ground loops. Either Bill Whitlock or
one of the other gurus said something along the lines of ground is a
equal potential myth used by engineers to make their jobs easier.
The exact wording and source of that aphorism are temporarily lost
to me. It's Whitlock who definitely dispels other myths about trying to
use thicker grounds or multiple grounds to fight loops.


when I took and emi class at uni one of the first thing the guy said was
something along the line of "ground does not exist"

It is usually in the form "universal ground _potential_ doesn't
exist", all ground potentials are different. Absolute ground potential
doesn't exist even in Sevre outside Paris, where they used to keep the
standard kilogram prototype and the standard meter prototype .

While there has been a lot of discussion in this thread about
grounding topologies inside the box, things get nasty when boxes are
connected together with perhaps a large distances between boxes.

A good practice is to have three separate grounding networks on site,
one for mains neutral N, one for the PE network and a separate
Technical/functional earth TE/FE networks. Each of these networks have
dedicated bars at the mains entry point of the building or complex. At
exactly this single point only the three bars are joined together with
jumpers as thick as your thumb. When the system is down, the jumpers
can be removed and measurements can be made to check that the networks
are truly separate.

The N network is polluted by mains return current of a single phase
system or the current imbalance in a three phase system. Even in a
balanced three phase system the third harmonics due to rectifier load
will pollute the neutral.

Mains power supply filters are usually connected to the PE, so it is
polluted by power supply noise.

Signal grounds are usually connected to the hopefully clean TE/FE
network. This requires that no equipments which has a signal ground
connected to the chassis and then to the PE are connected to TE/FE,
since a single mains filters will pollute the whole TE/FE network.

For this reason N, PE and signal grounds (TE/FE) should ne kept
separated and all three brought to the connection pins of a box, so
that they can be connected to three separate ground networks.

I have noticed a problem with some installers in foreign countries
that when they notice these three ground terminals they simply connect
jumpers between these terminals outside the box and use a single wire
for a connecting to mains neutral, now actually PEN :-(

Does a single-phase power plug have four prongs? Or five?




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Tim Williams]

"John Larkin" <jlarkin@highlandSNIPMEtechnology.com> wrote in message
news:e9ljke5qrs1q39qj112m3fbtmqhlt0uqqm@4ax.com...

Pretty much the entire upper-right quadrant. The prime power is 24
volts DC which we were required to isolate. It's huge and noisy by the
standards of a 12-bit 250 MHz ADC. Not "reading trash."

The CW multiplier string is to make up to 75 volts for an EUV
photodiode.

That's... huge?

I may have to get you a dictionary.

That's board level. Ground plane takes care of that. Do the same usual
thing on the board, keep loops local and avoid passing signals across it,
and you're fine.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tim Williams]

"Arie de Muynck" <no.spam@no.spam.org> wrote in message
news:5d49d917$0$10264$e4fe514c@news.xs4all.nl...

The way to avoid ground loop errors is to keep signals differential.


Or using a current not a voltage as signal.

But then you get induced [electric] currents corrupting your signal.

No free lunch. Use differential regardless.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

On Monday, 5 August 2019 15:20:18 UTC+1, Winfield Hill wrote:

Here's a DRAFT copy of x-Chapter 1x.1, which starts
things off, by dealing with wire and connectors.
Comments and corrections please.

https://www.dropbox.com/s/kz335xwvl5v8gie/1x.1_Wire-%26-Connectors_DRAFT.pdf?dl=1

"Now for the connector types to avoid (reasons withheld – just trust us!)"

that won't cut any ice, and the advice is wrong. Try selling consumer grade audio gear with odd connectors, see how that works out. Edison mains plugs are easy to criticise too, should we put something else on our mains products? Aluminium Belling-Lee UHFs are particularly awful, but without explanation it tells the reader nothing.


NT

 

On Tue, 6 Aug 2019 23:11:52 -0500, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

"Arie de Muynck" <no.spam@no.spam.org> wrote in message
news:5d49d917$0$10264$e4fe514c@news.xs4all.nl...
The way to avoid ground loop errors is to keep signals differential.


Or using a current not a voltage as signal.


But then you get induced [electric] currents corrupting your signal.

With standard 20 mA current loop driven from a 24 Vdc supply will
carry nearly 0.5 W signal power, thus a quite strong interference is
needed to disturb the signal.

Using twisted pairs .e.g. telephone cables also limits the induced
interference.

Current loops have been done with optoisolators for nearly half a
century, so you also get galvanic isolation for 'free'. Powering the
loop always from the transmitter side, the receiver can be passive
(an IR LED) so no ground potential issues between boxes.
..

No free lunch. Use differential regardless.

Properly terminated RS-422 line is essentially a bipolar current loop.

Tim

 

[Jan Panteltje]

On a sunny day (Tue, 6 Aug 2019 18:24:32 -0400) it happened Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote in
<qicun2$rn7$2@dont-email.me>:

On 8/6/19 2:43 PM, Tim Williams wrote:
"Jan Panteltje" <pNaOnStPeAlMtje@yahoo.com> wrote in message
news:qicbcm$ckr$1@dont-email.me...
I just wished people would no longer use filenames like
ThisSchematicIsTheLatestAndGreatest.PDF
3x.20_Precision-1.5kV-1us-Ramp_WH.pdf


My favorite is the,

Customer Project 12345_dingleBerryPOWERSUPPLY_REV_E.SCH

A true blend of DOS-style ALLCAPS (but still using LFNs?),
caps-avoidance, underscores (when a space apparently isn't available?)
AND spaces (oh..).

Working with other people has only reinforced my understanding that the
90-10 rule applies no matter how "educated" a group you're sampling...

Tim


I use camel case e.g. because it helps a lot finding the right file from
my archives, e.g.

2019-08-05-InvoiceABC05.pdf
TLV431AshuntRefOnSemiUnstableHorribleAvoidAvoid.pdf

~ # locate 3055 | grep -i pdf
/root/download/html/2N3055-D.pdf

 

On Tue, 6 Aug 2019 18:21:57 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 3:57 PM, upsidedown@downunder.com wrote:
On Tue, 6 Aug 2019 08:41:09 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 6. august 2019 kl. 17.06.48 UTC+2 skrev Don Kuenz:
Tim Williams <tiwill@seventransistorlabs.com> wrote:
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:cavhkeppudjiempknhs0jb84jpkau3sgo8@4ax.com...
Signal integrity is easy. PCB layer 2 is solid ground plane. Bolt it,
and grounded connector shells, to the metal box in as many places as
possible.

Cable shields to the box ditto.


Not really. Suppose there's a huge noisy inverter in the box. Ground loop
currents once again. Cables simply tied "shields to the box", and PCB
"bolt[ed] ... to the metal box", draws those currents into both. Now your
precision ADCs are all reading trash.

But with visibility to where the currents are flowing, or with a
star-grounding scheme, those loop currents stay separate. Say the
connectors are clustered on a front panel, shields grounded to it. That
keeps outside noise out, good. Collect the interior cables (which are still
all grounded to the same point, preferably as coaxially as possible, no
weedy wire links), and bundle them into a single harness. Ferrite beads as
needed. They go over to the PCB, which no longer needs chassis ground at
all.

Or do the brute-force method and use welded chassis compartments to keep the
bignasty away from the quietstuff. Cost doesn't much matter in your test
equipment, but it's a very real tradeoff in production. Production even
likes to avoid metal if they can...

My recent audio mix-amp project motivated me to read, or at least skim,
dozens of articles about /audio/ ground loops. Either Bill Whitlock or
one of the other gurus said something along the lines of ground is a
equal potential myth used by engineers to make their jobs easier.
The exact wording and source of that aphorism are temporarily lost
to me. It's Whitlock who definitely dispels other myths about trying to
use thicker grounds or multiple grounds to fight loops.


when I took and emi class at uni one of the first thing the guy said was
something along the line of "ground does not exist"

It is usually in the form "universal ground _potential_ doesn't
exist", all ground potentials are different. Absolute ground potential
doesn't exist even in Sevre outside Paris, where they used to keep the
standard kilogram prototype and the standard meter prototype .

While there has been a lot of discussion in this thread about
grounding topologies inside the box, things get nasty when boxes are
connected together with perhaps a large distances between boxes.

A good practice is to have three separate grounding networks on site,
one for mains neutral N, one for the PE network and a separate
Technical/functional earth TE/FE networks. Each of these networks have
dedicated bars at the mains entry point of the building or complex. At
exactly this single point only the three bars are joined together with
jumpers as thick as your thumb. When the system is down, the jumpers
can be removed and measurements can be made to check that the networks
are truly separate.

The N network is polluted by mains return current of a single phase
system or the current imbalance in a three phase system. Even in a
balanced three phase system the third harmonics due to rectifier load
will pollute the neutral.

Mains power supply filters are usually connected to the PE, so it is
polluted by power supply noise.

Signal grounds are usually connected to the hopefully clean TE/FE
network. This requires that no equipments which has a signal ground
connected to the chassis and then to the PE are connected to TE/FE,
since a single mains filters will pollute the whole TE/FE network.

For this reason N, PE and signal grounds (TE/FE) should ne kept
separated and all three brought to the connection pins of a box, so
that they can be connected to three separate ground networks.

I have noticed a problem with some installers in foreign countries
that when they notice these three ground terminals they simply connect
jumpers between these terminals outside the box and use a single wire
for a connecting to mains neutral, now actually PEN :-(


That fancy approach works great until you find yourself working next to
a big VF motor drive.

What is a big VFD ? I have only experience with a few dozen VFDs, each
in the 10-100 kW range. Control signals with 20 mA current loops.

At that point, squeezing everything onto one board and keeping the loop
areas tiny is a big help.

Cheers

Phil Hobbs

Cheers

Phil Hobbs

 

[Jan Panteltje]

On a sunny day (Tue, 6 Aug 2019 20:41:00 -0700 (PDT)) it happened
tabbypurr@gmail.com wrote in
<d34a9ea0-ed89-4c5e-865f-70a45119215c@googlegroups.com>:

On Wednesday, 7 August 2019 03:42:29 UTC+1, Phil Hobbs wrote:
On 8/6/19 10:44 AM, Don Kuenz wrote:

A stripping machine sure seems better for my own health than dipping one
end into a solder pot (IIRC) or a jar of paint remover.

The vapour pressure of lead at soldering temperatures is very low. So
solder pots are pretty safe as long as you don't tip it over on yourself.

Or nearly fall over & stick your hand in it. Or not pay attention for a moment & in it goes. I don't mind using them but don't
regard them as safe.

I have a very small one:
http://panteltje.com/pub/crucible_with_molten_solder_IMG_5439.JPG

works for plutonium too:
http://impiousdigest.com/wp-content/uploads/2016/01/plutoniummolten2.gif

Nothing to worry about.

 

[Tim Williams]

<upsidedown@downunder.com> wrote in message
newsjnkke5qbdius6qf4f8a6af8i62e7koag2@4ax.com...

currents corrupting your signal.

With standard 20 mA current loop driven from a 24 Vdc supply will
carry nearly 0.5 W signal power, thus a quite strong interference is
needed to disturb the signal.

Unless it's quite precise. Recently had a customer ask for 24-bit inputs.
Ended up with a precision burden resistor, channel mux, in-amp and a TI SPI
ADC.

Noise floor looks close to what the datasheet claims, so that's good news
about my front end. CMRR isn't bad, is visible but of a similar magnitude
(~100 counts over the input range). And hey, resistor matching, what do you
expect. (I added functionality so they can measure VCM and calibrate it out
in software if they want. And yes, customer's handing software.)

Since the inputs are filtered and essentially unloaded (only the filter
caps, mux switch, and in-amp input leakages), the inputs float very nicely,
and can be biased (in the common mode) by a touch of the finger. There is
some sequential charge transfer between channels, due the mux.

They couldn't give me a hard commitment on what ground reference or
polarity* the 4-20mA channels might be, so I had to do this (your
traditional +/-15V AFE). It's a 24V system and they really would've rather
had a 30V range, but that gets harder and harder to pull off (not so hard
regarding precision amps, but analog switches?).

*In the sense that there are high-side and low-side drivers. In an ideal
world, these are on isolated circuits so it doesn't matter, but, you know.
But it's a current loop, right? We don't care about voltage, the current
cures all!...Right? (See what really happens here?)

Using twisted pairs .e.g. telephone cables also limits the induced
interference.

Yup, pretty nice. Unless there's a nick in the insulation and now you have
current leakage from one or the other line...

Current loops have been done with optoisolators for nearly half a
century, so you also get galvanic isolation for 'free'. Powering the
loop always from the transmitter side, the receiver can be passive
(an IR LED) so no ground potential issues between boxes.

Optos are terrible! Unstable gain, poor distortion, slow speed. Fine for
serial. Basically useless above say 8 ENOB, and a few megbits.

No free lunch. Use differential regardless.

Properly terminated RS-422 line is essentially a bipolar current loop.

It's also a bipolar voltage pair. "Properly terminated" being the key word
there. It is necessarily and simultaneously both! Concentrating on just
one is setting yourself up for edge cases in the other.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tim Williams]

<upsidedown@downunder.com> wrote in message
news:6cqkket4ruh3dspnsn49jfn47u7pc9vn71@4ax.com...

That fancy approach works great until you find yourself working next to
a big VF motor drive.

What is a big VFD ? I have only experience with a few dozen VFDs, each
in the 10-100 kW range. Control signals with 20 mA current loops.

I would dare say any size VFD is "big" enough, if it's badly filtered.
Hundreds of volts swing, unshielded cables? Going from 100W to 100kW is
only a few dB more volts; sure it's many more dB of amps, but the amps don't
radiate quite as much.

It depends, of course. The normal case is, the amps are mostly filtered by
winding inductance. In that case, the offending radiation is mostly due to
switching voltage times cable capacitance, and not so dependent on load
current.

You can filter out that kind of noise, if you don't mind that all your
signals become ~ms scale status signals. Good luck getting real data
through there; shielded cables and isolated transceivers are basically
mandatory.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

On Wed, 7 Aug 2019 01:28:10 -0500, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

upsidedown@downunder.com> wrote in message
news:6cqkket4ruh3dspnsn49jfn47u7pc9vn71@4ax.com...
That fancy approach works great until you find yourself working next to
a big VF motor drive.

What is a big VFD ? I have only experience with a few dozen VFDs, each
in the 10-100 kW range. Control signals with 20 mA current loops.


I would dare say any size VFD is "big" enough, if it's badly filtered.
Hundreds of volts swing, unshielded cables? Going from 100W to 100kW is
only a few dB more volts; sure it's many more dB of amps, but the amps don't
radiate quite as much.

Have you looked at the current waveform of a simple old style six
pulse rectifier. ? It contains quite a lot of high harmonics. Current
requirements usually require some kind of PFC, for instance a 12 pulse
rectifier.

Then there are the PWM drive side, which should use shielded power
cables to the motor to reduce radiation, even if there are some filter
in at VFD output.

It depends, of course. The normal case is, the amps are mostly filtered by
winding inductance. In that case, the offending radiation is mostly due to
switching voltage times cable capacitance, and not so dependent on load
current.

You can filter out that kind of noise, if you don't mind that all your
signals become ~ms scale status signals. Good luck getting real data
through there; shielded cables and isolated transceivers are basically
mandatory.

Tim