Trigger Isolator

[Gary Pace]

Hi Y'all :

I need to simultaneously (within a few 10's of ns) trigger a number (4)
battery powered 'scopes from a single trigger event.

The problem is that each 'scope is at a different reference ground. I have
high dV/dt's between the "grounds" so isolation transformers have too much
C.

Obviously, I could design myself a circuit with a battery powered trigger
comparator feeding the LED's of 4 high speed opto's with four battery
powered secondary circuits giving the trigger signals to the 'scopes.

Is there a better way ? Does anybody make a suitable signal isolator ?

Thanks
Gary

 

[Joerg]

Hello Gary,

I need to simultaneously (within a few 10's of ns) trigger a number (4)
battery powered 'scopes from a single trigger event.

Assuming this is 10 or 20 nsec and not a 10th of a nsec. That makes it easy.

The problem is that each 'scope is at a different reference ground. I have
high dV/dt's between the "grounds" so isolation transformers have too much
C.

Obviously, I could design myself a circuit with a battery powered trigger
comparator feeding the LED's of 4 high speed opto's with four battery
powered secondary circuits giving the trigger signals to the 'scopes.

Is there a better way ? Does anybody make a suitable signal isolator ?

I use #43 ferrite toroids for that. Four to five bifilar turns
(twisted), one winding to the trigger input and the other to wherever
trigger is coming from. You'll need a C in series with the primary if
your trigger source doesn't like a DC short. The number of turns depends
on how sluggish the signal slope is. If rise times exceed 100nsec you
may need more than five turns bifilar.

If you take wire with a fairly thick insulation on a 1/2" OD core the
capcitance is just a few pF. If higher voltage spikes could be present
between primary and secondary use 20mil Teflon insulated wire or
something similar. Make sure the core has no burrs or carefully sand
these down before winding.

Don't use ferrite material that was intended for switche mode power
supplies (#77 and the like). It won't be any efficient in the nsec range.

If it's lots of scopes and the trigger source can't stomach all these
loads you may have to follow with CMOS buffers there (HC series bus
drivers or Schmitt inverters if slopes are slow). One for each toroid.
They don't like DC shorts so you'll need the caps.

Regards, Joerg

http://www.analogconsultants.com

 

[John Larkin]

On Sat, 23 Jul 2005 22:16:59 GMT, "Gary Pace" <xxx@yyy.com> wrote:

Hi Y'all :

I need to simultaneously (within a few 10's of ns) trigger a number (4)
battery powered 'scopes from a single trigger event.

The problem is that each 'scope is at a different reference ground. I have
high dV/dt's between the "grounds" so isolation transformers have too much
C.

Obviously, I could design myself a circuit with a battery powered trigger
comparator feeding the LED's of 4 high speed opto's with four battery
powered secondary circuits giving the trigger signals to the 'scopes.

Is there a better way ? Does anybody make a suitable signal isolator ?

Thanks
Gary

How about this:

Get a ferrite torroid and make 5 windings, each a couple turns of
well-insulated wire at the very end of a hank of coax. One coax is the
trigger-in signal, and four are the fanouts to the scopes. Space them
about the core evenly, I guess. You'll need a fairly hefty trigger-in
signal, solid TTL at the very least, to induce suitably hefty pulses
into the four loads. A fast dmos fet, 2N7000 or such, blasting 20
volts or so would be even juicier. Terminate at each scope. If your
common-mode noise level is severe, add clamp-on common-mode ferrites
in all lines.

Should work. Next step up would probably be fiber optics, a heap more
work.


Hey, look at this:

http://www.highlandtechnology.com/DSS/J720-730DS.html

I designed this for a guy who does EMP testing of military gear. He's
triggering a bunch of digitizers in an EMI environment in the vicinity
of 50,000 v/m, inducing thousands of amps into the poor things he's
testing. It's likely way overkill for your app... we just posted it to
see if anybody else might be interested, and because they're so cute.


John

 

[Joerg]

Hello John,

Get a ferrite torroid and make 5 windings, each a couple turns of
well-insulated wire at the very end of a hank of coax. One coax is the
trigger-in signal, and four are the fanouts to the scopes. Space them
about the core evenly, I guess. ...

You need #43 material or similar and the coupling might get a bit too
loose. If it has to be all on one toroid I'd twist them all gently
together and then wind. Or I should say, wrestle it around the core.
Let's see, how would that be called? Quintufilar or something like that?

... You'll need a fairly hefty trigger-in
signal, solid TTL at the very least, to induce suitably hefty pulses
into the four loads. A fast dmos fet, 2N7000 or such, blasting 20
volts or so would be even juicier. Terminate at each scope. If your
common-mode noise level is severe, add clamp-on common-mode ferrites
in all lines.

Big old bus drivers should do. When in the same chip they can often be
paralleled for more oompf.

http://www.highlandtechnology.com/DSS/J720-730DS.html

Nice housings. Looks upscale and expensive.

Regards, Joerg

http://www.analogconsultants.com

 

[John Larkin]

On Sun, 24 Jul 2005 00:20:26 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello John,

Get a ferrite torroid and make 5 windings, each a couple turns of
well-insulated wire at the very end of a hank of coax. One coax is the
trigger-in signal, and four are the fanouts to the scopes. Space them
about the core evenly, I guess. ...

You need #43 material or similar and the coupling might get a bit too
loose. If it has to be all on one toroid I'd twist them all gently
together and then wind. Or I should say, wrestle it around the core.
Let's see, how would that be called? Quintufilar or something like that?

Hi, Joerg,

I've done pretty fast stuff with a high-mu core and separated
windings. The tradeoff here is more capacitive coupling (with
multifilar) versus slower risetimes (separated windings.) Since the op
needs tens of ns response, pig slow, I'd think that separated would
work OK. Either way, it's easy to try.

... You'll need a fairly hefty trigger-in
signal, solid TTL at the very least, to induce suitably hefty pulses
into the four loads. A fast dmos fet, 2N7000 or such, blasting 20
volts or so would be even juicier. Terminate at each scope. If your
common-mode noise level is severe, add clamp-on common-mode ferrites
in all lines.

Big old bus drivers should do. When in the same chip they can often be
paralleled for more oompf.

And/Or drive it bridge-wise on the trigger side for twice the bang.

http://www.highlandtechnology.com/DSS/J720-730DS.html

Nice housings. Looks upscale and expensive.

The laser gadget is something like $180, and the receiver is maybe
$350. I can never remember the prices of anything. Even if you never
sell stuff like this to anybody else, it makes press releases.

John

 

[Joerg]

Hello John,

I've done pretty fast stuff with a high-mu core and separated
windings. The tradeoff here is more capacitive coupling (with
multifilar) versus slower risetimes (separated windings.) Since the op
needs tens of ns response, pig slow, I'd think that separated would
work OK. Either way, it's easy to try.

Yes, if he can tolerate a tiny deviation between the individual triggers
it should indeed be ok here.

Another option for those who hate winding toroids or don't have cores
handy is Ethernet. Often these cards contain a set of four transformers
(Murata etc.) in a block. Probably they should be good if the common
mode spikes don't exceed 500V. The stunner came when I needed one of
these quickly because the client didn't have cores and shipping took too
long. It was cheaper to buy an Ethernet card than buying the isolation
xfmrs as a part. I guess a cheap port switch would have been even more
of a bargian because it should contain lots of them.

The laser gadget is something like $180, and the receiver is maybe
$350. I can never remember the prices of anything. Even if you never
sell stuff like this to anybody else, it makes press releases.

Do you find it easy to get press releases published in the EE media? I
have never done it there, just in the medical world. There it often
helps if a "luminary" uses the gear or at least comments on it.

Regards, Joerg

http://www.analogconsultants.com

 

Have you ever looked at high frequency pulse transformers - not the
one's intended for triggering triacs, but those aimed at digital and
data processing?

IIRR Newport offered a bunch of parts that did the job. I last looked
at using their pars for this sort of job 15 years ago, but it looks as
if their 766 series - some of which are available from Farnell (order
codes 179-984 to 179-987) - might be worth looking at.

When I looked at them, it seemed to me that they had to be bifilar
wound as transmission line transformers, from the inter-winding
capacitance, and that is precisely what you and John Larkin are
recommending, as I would have done if I'd posted a response last night.

Because they are transmission line transformers, high permeability
manganese-zinc ferrite cores seem to give the same sort of rise-times
as nickel-zince ferrites, even though MnZn is lossier at high
frequencies.

-----------
Bill Sloman, Nijmegen

 

[John Larkin]

On Sun, 24 Jul 2005 00:59:52 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Do you find it easy to get press releases published in the EE media? I
have never done it there, just in the medical world. There it often
helps if a "luminary" uses the gear or at least comments on it.

If you have an interesting product and a nice picture, and you blanket
20-50 mags with press releases, odds are pretty good a few will pick
it up. If you're lucky, you'll get into the online editions too, and
get a link, and that improves your Google status.

The problem with a small business making niche products is that it's
so hard to connect with your potential customers scattered around the
world. So press releases and links and stuff are necessary to
gradually build up visibility and momentum.

John

 

[Joerg]

Hello Bill,

Have you ever looked at high frequency pulse transformers - not the
one's intended for triggering triacs, but those aimed at digital and
data processing?

I did, sometimes. But the minute I saw the price tags I decided it's
better for the client to roll their own or contract that out. Much
cheaper. Lots of times you can also find a ready-to-go "catalog
transformer" from companies such as Murata. They just aren't advertised
as pulse transformer but more for their target markets, such as modems
or LAN ports.

IIRR Newport offered a bunch of parts that did the job. I last looked
at using their pars for this sort of job 15 years ago, but it looks as
if their 766 series - some of which are available from Farnell (order
codes 179-984 to 179-987) - might be worth looking at.

Almost 7 Euros. A lot of money, unless it's for a prototype. For
production runs that usually won't fly.

Because they are transmission line transformers, high permeability
manganese-zinc ferrite cores seem to give the same sort of rise-times
as nickel-zince ferrites, even though MnZn is lossier at high
frequencies.

Usually I just look what's there from the mainstream manufacturers and
then design the xfmr around that. #43 works great in this application
and is very cheap.

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hello John,

If you have an interesting product and a nice picture, and you blanket
20-50 mags with press releases, odds are pretty good a few will pick
it up. If you're lucky, you'll get into the online editions too, and
get a link, and that improves your Google status.

Thanks, that sound like a good strategy.

The problem with a small business making niche products is that it's
so hard to connect with your potential customers scattered around the
world. So press releases and links and stuff are necessary to
gradually build up visibility and momentum.

That is true. I always wonder why there isn't any kind of exchange for
technology services. A place where managers could come to when they are
at the end of the rope and need someone they can't find in-house.

Regards, Joerg

http://www.analogconsultants.com

 

[John Larkin]

On Sun, 24 Jul 2005 20:47:38 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello John,

If you have an interesting product and a nice picture, and you blanket
20-50 mags with press releases, odds are pretty good a few will pick
it up. If you're lucky, you'll get into the online editions too, and
get a link, and that improves your Google status.

Thanks, that sound like a good strategy.

The problem with a small business making niche products is that it's
so hard to connect with your potential customers scattered around the
world. So press releases and links and stuff are necessary to
gradually build up visibility and momentum.

That is true. I always wonder why there isn't any kind of exchange for
technology services. A place where managers could come to when they are
at the end of the rope and need someone they can't find in-house.

Regards, Joerg

http://www.analogconsultants.com

Hey look, it worked!

http://www.electronics-express.com/interconnects/brief/showArticle.jhtml?articleID=166400598

Of course, this is buried pretty deep in an obscure list of new
product releases under the heading "interconnects", so it's not real
likely anybody will find this starting at the E-E home page. But press
releases do create more search-engine targets, and the link on this
page does boost us in Google's scoring system.

The advertising concept of "building a public presence" never made
sense for small businesses, but has new meaning in the age of search
engines.

John

 

[Joerg]

Hello John,

Hey look, it worked!

http://www.electronics-express.com/interconnects/brief/showArticle.jhtml?articleID=166400598

Yes, that's great! Interesting, you went metric in the text. Kilometers.
The only other places I see that in the US are IEEE publications.

Of course, this is buried pretty deep in an obscure list of new
product releases under the heading "interconnects", so it's not real
likely anybody will find this starting at the E-E home page. But press
releases do create more search-engine targets, and the link on this
page does boost us in Google's scoring system.

The advertising concept of "building a public presence" never made
sense for small businesses, but has new meaning in the age of search
engines.

Yes, it sure does. However, there still is a huge vacuum when it comes
to finding the right talent for a project of limited scope where people
don't need to hire someone permanent. When they are just looking for
someone or some company that can fix a dilemma or take over a nasty part
of a design.

Regards, Joerg

http://www.analogconsultants.com

 

[Fred Bloggs]

John Larkin wrote:

Hey look, it worked!

http://www.electronics-express.com/interconnects/brief/showArticle.jhtml?articleID=166400598

What does "+5 volt nominal behind 50 ohms, BNC connector" mean exactly
for that J720 "INPUT"? - wish you did not use that crummy SMB for the
J730 digital output...And how rugged is that ST-ST fiber patch cord
anyway? Is it some dainty lab type thing or can it withstand being
manhandled and pulled through conduits not so gently and repeatedly? And
this product runs roughly $500 for an xmt/rcv pair?

 

[John Larkin]

On Thu, 04 Aug 2005 10:17:26 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

John Larkin wrote:


Hey look, it worked!

http://www.electronics-express.com/interconnects/brief/showArticle.jhtml?articleID=166400598


What does "+5 volt nominal behind 50 ohms, BNC connector" mean exactly
for that J720 "INPUT"? -

Well, if you had a 50 ohm resistor, and behind it you had a 5-volt
source, then, well, there you'd be. And a BNC is a sort of round shiny
gadget used to help connect coaxial cables from some things to other
things.

wish you did not use that crummy SMB for the
J730 digital output...

I like SMBs. I like MCXs even more, but they're not as common in my
user base, and don't detent very hard so are more likely to work
loose. No complaints so far, plus we get to sell SMB-BNC cables as
accessories. No way I could have fitted BNCs into that tiny box, and
SMAs are just too much a pain to screw/unscrew all the time. Don't
even mention LEMOS to me.

And how rugged is that ST-ST fiber patch cord
anyway? Is it some dainty lab type thing or can it withstand being
manhandled and pulled through conduits not so gently and repeatedly?

No fiber optic connector is well-suited to use by lumberjacks standing
in mud. But you might note that this message to you is no doubt being
transmitted over fiber optics that has been pulled through pipes
buried in ditches, clear across the country, by regular worker-guys.

Lots of fiber is being installed in cities and buildings lately,
mostly actually blow-in and not literally "pulled." The fiber is so
thin and light and flexible, you just clip a sort of little parachute
to it, stick it in a conduit, and air-blast it all the way, around
corners and everything.

What's astounding about fiber is the quality of fast signals over
distance; multimode fiber has a bit of dispersion, maybe a ns per km,
but nothing like the ghastly skin-effect losses of copper. Single-mode
is even better.

STs are pretty good, easy to mate/unmate and quite reliable; ST cables
are available off the shelf at at Fry's, and are used for audio and
ethernet links.

And
this product runs roughly $500 for an xmt/rcv pair?

Yeah. People are surprised at how cheap they are. We're gonna have to
raise the price eventually. I actually did this for a guy at Arnold
AFB who does EMP testing of military gear, at field strengths of
50,000 v/m. I just did the fiber stuff to get him to buy the serious
timing hardware.

John

 

[Fred Bloggs]

John Larkin wrote:

What does "+5 volt nominal behind 50 ohms, BNC connector" mean exactly
for that J720 "INPUT"? -


Well, if you had a 50 ohm resistor, and behind it you had a 5-volt
source, then, well, there you'd be.

That still makes no sense- so skip it.

And a BNC is a sort of round shiny
gadget used to help connect coaxial cables from some things to other
things.

If that's your attitude then keep them.

 

[John Larkin]

On Fri, 05 Aug 2005 12:51:12 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

What does "+5 volt nominal behind 50 ohms, BNC connector" mean exactly
for that J720 "INPUT"? -


Well, if you had a 50 ohm resistor, and behind it you had a 5-volt
source, then, well, there you'd be.

That still makes no sense- so skip it.

I thought that terminology was fairly common: an open-circuit voltage
source of 5 volts, with a 50-ohm source impedance. Not to be confused
with a 50-ohm source that puts 5 volts onto 50 ohms, which would be
"ten volts behind 50 ohms". If you just say "5 volts at 50 ohms" it
can be taken either way.

And a BNC is a sort of round shiny
gadget used to help connect coaxial cables from some things to other
things.

If that's your attitude then keep them.

Sorry. Don't know how else to explain "BNC" connector.

John