What are good ways to protect from lightning induced transients on
low-level signal liines such as 0-100 mV differential input over twisted
pair between transducer and opamps, while minimizing corruption of the
signal during the time transients are not present? A strain guage for
example. ( I am talking about induced transients, not a direct lightning
hit.) My current interest is relative to on a boat, but perhaps putting
sensors external to the house also. I'm in the Tampa Bay area ---
lightning capital of the US. I've done a lot of searching on the web
but almost everything I found regarded protection of power supplies, and
some for telephone lines. Some "tried and true" experience would be
much appreciated.
Reminds me of an experience with an early network.
Every time we had a thunderstorm we would loose at least on "Line Driver" or "Line Receiver" IC, after isolating which one, I would cut the pins from the DIP and desolder them one at a time, then solder in a socket and plug in a new IC
(theory being it would be easier to replace next time)
But we discovered that the ones in sockets never failed, once we got them all socketed we never had another one blow out no matter how bad the storm.
I have often wondered if the small series inductance and parallel capacitance of the socket was giving a little extra protection???
For starters, with signal levels 0-100mv fast switching diodes would be a cheap and easy precaution.
A pair of them reversed parallel across the line would keep the differential below a volt.
And perhaps another similar set from each line to ground?
> What are good ways to protect from lightning induced transients on
> low-level signal liines such as 0-100 mV differential input over twisted
> pair between transducer and opamps, while minimizing corruption of the
> signal during the time transients are not present? A strain guage for
> example. ( I am talking about induced transients, not a direct lightning
> hit.) My current interest is relative to on a boat, but perhaps putting
> sensors external to the house also. I'm in the Tampa Bay area ---
> lightning capital of the US. I've done a lot of searching on the web
> but almost everything I found regarded protection of power supplies, and
> some for telephone lines. Some "tried and true" experience would be
> much appreciated.
> --
>Reminds me of an experience with an early network.
>Every time we had a thunderstorm we would loose at least on "Line Driver" or "Line Receiver" IC, after isolating which one, I would cut the pins from the DIP and desolder them one at a time, then solder in a socket and plug in a new IC
> (theory being it would be easier to replace next time)
>But we discovered that the ones in sockets never failed, once we got them all socketed we never had another one blow out no matter how bad the storm.
>
>
<respectful snip>
I had the same experience. What we decided was that the socket added a
tiny series resistance on all pins, that allowed the device to tolerate
line spikes. Soldering is a very low resistance connection; sockets are
considered medium resistance connections.
> Falcon Wireless Tech Support - KF4HAZ wrote:
>
> >Reminds me of an experience with an early network.
> >Every time we had a thunderstorm we would loose at least on "Line Driver" or "Line Receiver" IC, after isolating which one, I would cut the pins from the DIP and desolder them one at a time, then solder in a socket and plug in a new IC
> > (theory being it would be easier to replace next time)
> >But we discovered that the ones in sockets never failed, once we got them all socketed we never had another one blow out no matter how bad the storm.
> >
> >
>
> <respectful snip>
>
> I had the same experience. What we decided was that the socket added a
> tiny series resistance on all pins, that allowed the device to tolerate
> line spikes. Soldering is a very low resistance connection; sockets are
> considered medium resistance connections.
>
> --Bob
>
> --
Either that or the part of Murphees Law that states:
"if a part is easily replaced it is less likely to fail than one that is harder to replace"
> What are good ways to protect from lightning induced transients on low-level
> signal liines such as 0-100 mV differential input over twisted pair between
> transducer and opamps, while minimizing corruption of the signal during the
> time transients are not present? A strain guage for example. ( I am talking
> about induced transients, not a direct lightning hit.) My current interest
> is relative to on a boat, but perhaps putting sensors external to the house
> also. I'm in the Tampa Bay area --- lightning capital of the US. I've done
> a lot of searching on the web but almost everything I found regarded
> protection of power supplies, and some for telephone lines. Some "tried and
> true" experience would be much appreciated.
My limited experience relates to telecom and geophysical equipment. The
short version is, make all sensitive parts socketed, and keep spares.
More seriously, varistors fare reasonably well, as do tranzrobs and
active clamps. It is important to ground your system at one and exactly
one place, regardless of the size of the segment (even if this means
that you have to use double insulation and/or double shielding to
satisfy local code which requires local grounding everywhere). I don't
know much about boats except that welding 'grounding lugs' and then
assuming these are ground is a recipe for disaster.
If your application is related to remotely measuring force in a winch or
boom or such, I'd suggest to place the entire preamp next to the strain
gages and send 4-20mA or RS485 with remote power through the same cable.
> Reminds me of an experience with an early network. Every time we had a
> thunderstorm we would loose at least on "Line Driver" or "Line
> Receiver" IC, after isolating which one, I would cut the pins from the
> DIP and desolder them one at a time, then solder in a socket and plug
> in a new IC (theory being it would be easier to replace next time) But
> we discovered that the ones in sockets never failed, once we got them
> all socketed we never had another one blow out no matter how bad the
> storm. I have often wondered if the small series inductance and
> parallel capacitance of the socket was giving a little extra
> protection???
Were the replacement chips of the same make and manufacturers as the
originals (not version B etc ?). Most line failed (long) line drivers I
have seen have built-in fault indicators (like a crater in the epoxy).
I also understand that the manufacturers continuously improved line
drivers over time. E.g. I remember old 1488s destroyed but after a few
years they no longer died (easily).
> On Thu, 17 Mar 2005, Falcon Wireless Tech Support - KF4HAZ wrote:
>
> > Reminds me of an experience with an early network. Every time we had a
> > thunderstorm we would loose at least on "Line Driver" or "Line
> > Receiver" IC, after isolating which one, I would cut the pins from the
> > DIP and desolder them one at a time, then solder in a socket and plug
> > in a new IC (theory being it would be easier to replace next time) But
> > we discovered that the ones in sockets never failed, once we got them
> > all socketed we never had another one blow out no matter how bad the
> > storm. I have often wondered if the small series inductance and
> > parallel capacitance of the socket was giving a little extra
> > protection???
>
> Were the replacement chips of the same make and manufacturers as the
> originals (not version B etc ?). Most line failed (long) line drivers I
> have seen have built-in fault indicators (like a crater in the epoxy).
>
> I also understand that the manufacturers continuously improved line
> drivers over time. E.g. I remember old 1488s destroyed but after a few
> years they no longer died (easily).
>
> Peter
> --
Actually some were, while others were even earlier production code units from my personal stock, I still have IC's with date codes back to the 70's.
Comes from keeping a well stocked parts bin, you never know when you might have to repair that one of a kind unit you built 30+ years ago and finding a 74Fxxx 74Sxxx or some such, might be difficult by the time that thingy starts to have trouble ;-)
Back then if you were willing to spend a few hours on the phone (long distance) Fairchild would ship you a dozen or more of each part they manufactured as "Samples" and a call to the proper sales Rep. at the right time of the year could net you a bookshelf full of databooks for free! But that was before the internet...
engineer.cotse.net .
