Connectors for high-vibration environments with extremely low humidity...

[Phil Hobbs]

Hi, all,

So we\'re doing this multispectral sensor for finding smouldering fires
in heavy agricultural equipment. It has to operate outdoors in a
high-vibration environment over a case temperature range of about -20C
to +70C. The board is conformal-coated, but we need to avoid
condensation to keep the window from fogging up and avoid board leakage
that could trash the performance of the NIR channel, which uses a very
high-Z TIA.

Accordingly we\'re using IP68-rated M12 connectors and customized
enclosures with fancy O-ring seals, self-sealing screws, and
carefully-placed filtered vents to prevent pressure differences that
could transport liquid water to the interior of the box.

Because of the air exchange due to the vent, we\'re filling a major
fraction of the interior volume with Linde 5A molecular sieve in a Tyvek
envelope. (The envelopes are actually intended for use in steam
autoclaves for sterilizing surgical instruments, but they\'re just right
for this job.) We calculate on fairly pessimistic assumptions that the
interior ought to stay adequately dry for 25 years of service, which is
fine. There\'s a T/H sensor on the board, so the firmware can keep track
of whether there\'s any danger of condensation and report a fault if
there is.

So far it tests out well, but there are one or two loose ends that need
to be taken care of before we deploy the pilot run. Which brings me to
the question: what connectors to use in hot/cold and very dry
environments with lots of vibration. We need 8 positions including
power, ground, half-duplex RS485 MODBUS, and some analog signalling
outputs to talk to a PLC.

Nylon famously gets brittle and fails in that situation, so we\'re
looking at these: <http://www.jst-mfg.com/product/pdf/eng/ePA-F.pdf>

Specifically, we\'re tentatively planning to use the ones with
glass-filled polybutylene terephthalate housings: through-hole jacks and
crimp-on plugs (not the insulation-displacement ones). The solder will
be normal Sn63 because they don\'t grow cotton in Europe.

This is not our usual corner of the design space, so I\'d appreciate
comments from folks with relevant experience.

Thanks

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

 

[Clive Arthur]

On 11/08/2020 06:45, Phil Hobbs wrote:

Hi, all,

So we\'re doing this multispectral sensor for finding smouldering fires
in heavy agricultural equipment.  It has to operate outdoors in a
high-vibration environment over a case temperature range of about -20C
to +70C.  The board is conformal-coated, but we need to avoid
condensation to keep the window from fogging up and avoid board leakage
that could trash the performance of the NIR channel, which uses a very
high-Z TIA.

Accordingly we\'re using IP68-rated M12 connectors and customized
enclosures with fancy O-ring seals, self-sealing screws, and
carefully-placed filtered vents to prevent pressure differences that
could transport liquid water to the interior of the box.

Because of the air exchange due to the vent, we\'re filling a major
fraction of the interior volume with Linde 5A molecular sieve in a Tyvek
envelope.  (The envelopes are actually intended for use in steam
autoclaves for sterilizing surgical instruments, but they\'re just right
for this job.)  We calculate on fairly pessimistic assumptions that the
interior ought to stay adequately dry for 25 years of service, which is
fine.  There\'s a T/H sensor on the board, so the firmware can keep track
of whether there\'s any danger of condensation and report a fault if
there is.

So far it tests out well, but there are one or two loose ends that need
to be taken care of before we deploy the pilot run.  Which brings me to
the question: what connectors to use in hot/cold and very dry
environments with lots of vibration.  We need 8 positions including
power, ground, half-duplex RS485 MODBUS, and some analog signalling
outputs to talk to a PLC.

Nylon famously gets brittle and fails in that situation, so we\'re
looking at these: <http://www.jst-mfg.com/product/pdf/eng/ePA-F.pdf

Specifically, we\'re tentatively planning to use the ones with
glass-filled polybutylene terephthalate housings: through-hole jacks and
crimp-on plugs (not the insulation-displacement ones).  The solder will
be normal Sn63 because they don\'t grow cotton in Europe.

This is not our usual corner of the design space, so I\'d appreciate
comments from folks with relevant experience.

Thanks

Phil Hobbs

Glenair connectors are often specified for high vibration/temperature
downhole use, a bit like the old saw \"nobody ever got sacked for buying
IBM\".

MWDM2L-9SCBRP-.110-513 for example, that may be over the top but they do
several other types.

Check your bank balance first, and lead-free solder is tougher.

--
Cheers
Clive

 

[Tim Williams]

A client has the same application but in rugged automotive conditions
(mining equipment, etc.). They use a thermopile sensor. (They\'re detecting
direct flame; sounds like your case needs more sensitivity, so that probably
wouldn\'t go, and explains the TIA, with, I guess, a long wave photodiode or
pyroelectric sensor.)

I forget what the minimum temperature is (maybe it was more or less than
your requirement?), but they use M-series Turck connectors throughout.
Pigtail type, leads soldered directly to the board. Don\'t remember what
plastics they\'re made of or if they say, but they\'re rated for the service
in any case. And as much potting as possible, no direct route for moisture
to get in.

They do have problems with vibration of connectors causing dropouts of power
or signal. A recent change has been to put an MCU inside the boxes, so
instead of a DC signal, a serial keepalive message is sent, and the system
can be more aware of its integrity as well as more forgiving of momentary
dropout.

Not sure what you\'re showing with the rectangular header -- internal
board-to-board wiring? External connections??

Tim

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

\"Phil Hobbs\" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:2746d762-6fd6-b65d-69e4-0d6946a084b7@electrooptical.net...

Hi, all,

So we\'re doing this multispectral sensor for finding smouldering fires in
heavy agricultural equipment. It has to operate outdoors in a
high-vibration environment over a case temperature range of about -20C to
+70C. The board is conformal-coated, but we need to avoid condensation to
keep the window from fogging up and avoid board leakage that could trash
the performance of the NIR channel, which uses a very high-Z TIA.

Accordingly we\'re using IP68-rated M12 connectors and customized
enclosures with fancy O-ring seals, self-sealing screws, and
carefully-placed filtered vents to prevent pressure differences that could
transport liquid water to the interior of the box.

Because of the air exchange due to the vent, we\'re filling a major
fraction of the interior volume with Linde 5A molecular sieve in a Tyvek
envelope. (The envelopes are actually intended for use in steam
autoclaves for sterilizing surgical instruments, but they\'re just right
for this job.) We calculate on fairly pessimistic assumptions that the
interior ought to stay adequately dry for 25 years of service, which is
fine. There\'s a T/H sensor on the board, so the firmware can keep track
of whether there\'s any danger of condensation and report a fault if there
is.

So far it tests out well, but there are one or two loose ends that need to
be taken care of before we deploy the pilot run. Which brings me to the
question: what connectors to use in hot/cold and very dry environments
with lots of vibration. We need 8 positions including power, ground,
half-duplex RS485 MODBUS, and some analog signalling outputs to talk to a
PLC.

Nylon famously gets brittle and fails in that situation, so we\'re looking
at these: <http://www.jst-mfg.com/product/pdf/eng/ePA-F.pdf

Specifically, we\'re tentatively planning to use the ones with glass-filled
polybutylene terephthalate housings: through-hole jacks and crimp-on plugs
(not the insulation-displacement ones). The solder will be normal Sn63
because they don\'t grow cotton in Europe.

This is not our usual corner of the design space, so I\'d appreciate
comments from folks with relevant experience.

Thanks

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

 

[Robert Baer]

Phil Hobbs wrote:

Hi, all,

So we\'re doing this multispectral sensor for finding smouldering fires
in heavy agricultural equipment.  It has to operate outdoors in a
high-vibration environment over a case temperature range of about -20C
to +70C.  The board is conformal-coated, but we need to avoid
condensation to keep the window from fogging up and avoid board leakage
that could trash the performance of the NIR channel, which uses a very
high-Z TIA.

Accordingly we\'re using IP68-rated M12 connectors and customized
enclosures with fancy O-ring seals, self-sealing screws, and
carefully-placed filtered vents to prevent pressure differences that
could transport liquid water to the interior of the box.

Because of the air exchange due to the vent, we\'re filling a major
fraction of the interior volume with Linde 5A molecular sieve in a Tyvek
envelope.  (The envelopes are actually intended for use in steam
autoclaves for sterilizing surgical instruments, but they\'re just right
for this job.)  We calculate on fairly pessimistic assumptions that the
interior ought to stay adequately dry for 25 years of service, which is
fine.  There\'s a T/H sensor on the board, so the firmware can keep track
of whether there\'s any danger of condensation and report a fault if
there is.

So far it tests out well, but there are one or two loose ends that need
to be taken care of before we deploy the pilot run.  Which brings me to
the question: what connectors to use in hot/cold and very dry
environments with lots of vibration.  We need 8 positions including
power, ground, half-duplex RS485 MODBUS, and some analog signalling
outputs to talk to a PLC.

Nylon famously gets brittle and fails in that situation, so we\'re
looking at these: <http://www.jst-mfg.com/product/pdf/eng/ePA-F.pdf

Specifically, we\'re tentatively planning to use the ones with
glass-filled polybutylene terephthalate housings: through-hole jacks and
crimp-on plugs (not the insulation-displacement ones).  The solder will
be normal Sn63 because they don\'t grow cotton in Europe.

This is not our usual corner of the design space, so I\'d appreciate
comments from folks with relevant experience.

Thanks

Phil Hobbs

Sn63 is distinctly Europe non-RoHS!

 

[server]

>Sn63 is distinctly Europe non-RoHS!

Hence my comment about nobody in the EU growing cotton. For this one I don\'t have to care about Ro so-called HS.

Cheers

Phil Hobbs

 

[Phil Hobbs]

On 2020-08-11 03:29, Clive Arthur wrote:

On 11/08/2020 06:45, Phil Hobbs wrote:
Hi, all,

So we\'re doing this multispectral sensor for finding smouldering fires
in heavy agricultural equipment.  It has to operate outdoors in a
high-vibration environment over a case temperature range of about -20C
to +70C.  The board is conformal-coated, but we need to avoid
condensation to keep the window from fogging up and avoid board
leakage that could trash the performance of the NIR channel, which
uses a very high-Z TIA.

Accordingly we\'re using IP68-rated M12 connectors and customized
enclosures with fancy O-ring seals, self-sealing screws, and
carefully-placed filtered vents to prevent pressure differences that
could transport liquid water to the interior of the box.

Because of the air exchange due to the vent, we\'re filling a major
fraction of the interior volume with Linde 5A molecular sieve in a
Tyvek envelope.  (The envelopes are actually intended for use in steam
autoclaves for sterilizing surgical instruments, but they\'re just
right for this job.)  We calculate on fairly pessimistic assumptions
that the interior ought to stay adequately dry for 25 years of
service, which is fine.  There\'s a T/H sensor on the board, so the
firmware can keep track of whether there\'s any danger of condensation
and report a fault if there is.

So far it tests out well, but there are one or two loose ends that
need to be taken care of before we deploy the pilot run.  Which brings
me to the question: what connectors to use in hot/cold and very dry
environments with lots of vibration.  We need 8 positions including
power, ground, half-duplex RS485 MODBUS, and some analog signalling
outputs to talk to a PLC.

Nylon famously gets brittle and fails in that situation, so we\'re
looking at these: <http://www.jst-mfg.com/product/pdf/eng/ePA-F.pdf

Specifically, we\'re tentatively planning to use the ones with
glass-filled polybutylene terephthalate housings: through-hole jacks
and crimp-on plugs (not the insulation-displacement ones).  The solder
will be normal Sn63 because they don\'t grow cotton in Europe.

This is not our usual corner of the design space, so I\'d appreciate
comments from folks with relevant experience.

Thanks

Phil Hobbs

Glenair connectors are often specified for high vibration/temperature
downhole use, a bit like the old saw \"nobody ever got sacked for buying
IBM\".

MWDM2L-9SCBRP-.110-513 for example, that may be over the top but they do
several other types.

Check your bank balance first, and lead-free solder is tougher.

Thanks. I was perhaps unclear--the connector I\'m concerned about is
inside the case, connecting the short wiring harness from the M12
connector to the board. We\'re expecting to put some heat shrink tubing
on the wires to damp out vibration.

The issue we\'re concerned with at the moment is preventing the
connectors from crumbling into dust, which is the likely fate of nylon
connector shells in this environment.

Thanks

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

 

[Phil Hobbs]

On 2020-08-11 07:16, Tim Williams wrote:

A client has the same application but in rugged automotive conditions
(mining equipment, etc.).  They use a thermopile sensor.  (They\'re
detecting direct flame; sounds like your case needs more sensitivity, so
that probably wouldn\'t go, and explains the TIA, with, I guess, a long
wave photodiode or pyroelectric sensor.)

We have a visible channel, a SWIR channel (0.9-1.7 um), and a MWIR
channel (3-5 um). The SWIR detector is 0.3 mm in diameter, so it needs
a very high-Z TIA. (It uses two 100M resistors in series, shunted by a
series pair of very low leakage diodes so that it doesn\'t rail in bright
light.)

I forget what the minimum temperature is (maybe it was more or less than
your requirement?), but they use M-series Turck connectors throughout.
Pigtail type, leads soldered directly to the board.  Don\'t remember what
plastics they\'re made of or if they say, but they\'re rated for the
service in any case.  And as much potting as possible, no direct route
for moisture to get in.

I don\'t have any experience using potting, so I\'d be reluctant to use it
for this one. We do have to use goop between the board and box to keep
it from vibrating much.

Mining is a very dirty business indeed. I\'ve been down a few working
mines--underground, a mercury mine in BC (Pinchi Lake) and a gold mine
in the Northwest Territories (the Con) as well as an open pit lead/zinc
mine also in the NWT (Pine Point). My Dad used to work for the old
Cominco [not the company currently trading under that name], and he took
me with him on a tour of their operations in the North. It was pretty
cool--I was 12 at the time, and got to hold an 80-pound gold bar. (It
was 75% gold and 25% silver iirc.)

They do have problems with vibration of connectors causing dropouts of
power or signal.  A recent change has been to put an MCU inside the
boxes, so instead of a DC signal, a serial keepalive message is sent,
and the system can be more aware of its integrity as well as more
forgiving of momentary dropout.

Yeah, ours have an LPC845 Cortex M0+ in them. Nice part--32 MHz, with a
gigantic pin mux so you can have almost any function on (almost) any pin.

Not sure what you\'re showing with the rectangular header -- internal
board-to-board wiring?  External connections??

It\'s to go from the pigtailed M12 to the board.

We\'ve been going back and forth about soldering the wires directly to
the board, but have heard stories about vibration causing fatigue
failure at the stress concentration point where the tinned region ends,
as well as anecdotal wisdom about the goodness of crimped connections in
environments like that.

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

 

[Clive Arthur]

On 11/08/2020 19:01, Phil Hobbs wrote:

<snip>

Thanks.  I was perhaps unclear--the connector I\'m concerned about is
inside the case, connecting the short wiring harness from the M12
connector to the board.  We\'re expecting to put some heat shrink tubing
on the wires to damp out vibration.

The issue we\'re concerned with at the moment is preventing the
connectors from crumbling into dust, which is the likely fate of nylon
connector shells in this environment.

Thanks

Phil Hobbs

Glenair do that sort of thing. \'Latching Microstrips\' they call them.
Good quality stuff.

https://www.glenair.com/micro-d/q.htm

--
Cheers
Clive

 

[Clive Arthur]

On 11/08/2020 19:23, Phil Hobbs wrote:

<snip>

We\'ve been going back and forth about soldering the wires directly to
the board, but have heard stories about vibration causing fatigue
failure at the stress concentration point where the tinned region ends,
as well as anecdotal wisdom about the goodness of crimped connections in
environments like that.

Standard way is to loop the wire through holes adjacent to the solder
pads, so through the board with insulated wire, then double back through
a pad to solder. That is reliable.

If you have heavy parts - eg large through hole MOSFETs, then don\'t
solder them to the PCB, use looped wires soldered to their pins.
/Extreme/ vibration calls for potting, but a conformal silicone coating
is fine otherwise. And lead-free solder makes a stronger joint.

Place small parts along the least flexy direction, use Flexicap
capacitors, expect microphony. No BGAs, and be more generous with the
solder than normal.

--
Cheers
Clive

 

[Tim Williams]

\"Phil Hobbs\" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:7023e4dd-38c1-165a-2aed-75078864178c@electrooptical.net...

I don\'t have any experience using potting, so I\'d be reluctant to use it
for this one. We do have to use goop between the board and box to keep
it from vibrating much.

Yeah, automotive does that a lot. Not uncommon to see modules with
electrolytics sticking up from the muck.

Might do, then, to have just a little more, enough to cover where the wires
come out -- or put some extra goop around them?

And yeah, NASA doesn\'t like tinned wire either, indeed they have a whole
methodology for doing that correctly (which must be pretty inevitable for
the popularity of solder-cup MIL terminals?). If they can do it, it\'s
definitely possible; whether it\'s worth following that procedure, or maybe a
watered-down version of it, is a potentially costly question though. Alas,
I don\'t have that experience to offer...

Also a possibility, solder-in crimp termals. Seen \'em on ATX PSUs plenty of
times. Probably more of an assembly expedient than for reliability though?
(The crimp is basically just the barrel, no socket/pin. The barrel and wire
is what goes into the board to get soldered. There\'s usually a retention
tab, I assume to hold it in place for wave soldering.)

I think in my example, the connections are all hand soldered. Which has to
be a big adder to their assembly cost. It\'s not mass production quantities,
and they don\'t seem to have much competition (and for an end product that
doesn\'t have much competition in turn), so I guess they don\'t mind. YMMV.

Oh also, I forget what they do with the IR sensors, if they\'re fully potted,
or partial, and if they have a seal around the optics. Might be the latter.
Yet another thing to think about...

Mining is a very dirty business indeed. I\'ve been down a few working
mines--underground, a mercury mine in BC (Pinchi Lake) and a gold mine in
the Northwest Territories (the Con) as well as an open pit lead/zinc
mine also in the NWT (Pine Point). My Dad used to work for the old
Cominco [not the company currently trading under that name], and he took
me with him on a tour of their operations in the North. It was pretty
cool--I was 12 at the time, and got to hold an 80-pound gold bar. (It was
75% gold and 25% silver iirc.)

Very cool. Unless you were in one of those super deep mines that\'s over
40°C and full humidity, but other than that... :^)

They also like to wash down the trucks, and I mean using whatever is handy:
steam, seawater... Electrolysis in connectors (even if they\'re IP67) is
sometimes a problem too. At least you wouldn\'t have that problem I guess.

Yeah, ours have an LPC845 Cortex M0+ in them. Nice part--32 MHz, with a
gigantic pin mux so you can have almost any function on (almost) any pin.

Ah, yep, cheap too. Though I\'ve heard they\'re Microchip levels of buggy.
(Haven\'t looked at them in enough detail to know that myself.)

We use a ton of STM32s: affordable enough, easy to use (even supported by
Arduino, should you happen upon that route), not too many bugs.

Personally, I like AVR XMEGA, charming 8-bit machines, pricey though they
are. Fortunately, as a hardware guy, I just play with them; I\'m in no
danger of putting one into production. :^)

Tim

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

 

[Joe Gwinn]

On Tue, 11 Aug 2020 14:23:34 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-08-11 07:16, Tim Williams wrote:
A client has the same application but in rugged automotive conditions
(mining equipment, etc.).  They use a thermopile sensor.  (They\'re
detecting direct flame; sounds like your case needs more sensitivity, so
that probably wouldn\'t go, and explains the TIA, with, I guess, a long
wave photodiode or pyroelectric sensor.)

We have a visible channel, a SWIR channel (0.9-1.7 um), and a MWIR
channel (3-5 um). The SWIR detector is 0.3 mm in diameter, so it needs
a very high-Z TIA. (It uses two 100M resistors in series, shunted by a
series pair of very low leakage diodes so that it doesn\'t rail in bright
light.)


I forget what the minimum temperature is (maybe it was more or less than
your requirement?), but they use M-series Turck connectors throughout.
Pigtail type, leads soldered directly to the board.  Don\'t remember what
plastics they\'re made of or if they say, but they\'re rated for the
service in any case.  And as much potting as possible, no direct route
for moisture to get in.

I don\'t have any experience using potting, so I\'d be reluctant to use it
for this one. We do have to use goop between the board and box to keep
it from vibrating much.

Potting is very effective. But I\'d go talk to your local Master Bond
rep, and their application engineers.

Mining is a very dirty business indeed. I\'ve been down a few working
mines--underground, a mercury mine in BC (Pinchi Lake) and a gold mine
in the Northwest Territories (the Con) as well as an open pit lead/zinc
mine also in the NWT (Pine Point). My Dad used to work for the old
Cominco [not the company currently trading under that name], and he took
me with him on a tour of their operations in the North. It was pretty
cool--I was 12 at the time, and got to hold an 80-pound gold bar. (It
was 75% gold and 25% silver iirc.)

They do have problems with vibration of connectors causing dropouts of
power or signal.  A recent change has been to put an MCU inside the
boxes, so instead of a DC signal, a serial keepalive message is sent,
and the system can be more aware of its integrity as well as more
forgiving of momentary dropout.

Yeah, ours have an LPC845 Cortex M0+ in them. Nice part--32 MHz, with a
gigantic pin mux so you can have almost any function on (almost) any pin.

Not sure what you\'re showing with the rectangular header -- internal
board-to-board wiring?  External connections??

It\'s to go from the pigtailed M12 to the board.

We\'ve been going back and forth about soldering the wires directly to
the board, but have heard stories about vibration causing fatigue
failure at the stress concentration point where the tinned region ends,
as well as anecdotal wisdom about the goodness of crimped connections in
environments like that.

There are some kinds of metal-pin connector that are *very*
vibration-resistant, ones having a cage of hyperbolic contact wires
pinching a solid male pin. The patents have long since expired, so
there are mnay makers. Here is one:

..<https://www.smithsinterconnect.com/SmithsInterconnect/files/83/83fbee10-28e1-4598-952d-340ee65770a5.pdf>

There was another family where the male pin was a birdcage of smaller
wires that were pushed into a slightly undersize cylindrical tube
female pin, but I can\'t find these any more. Probably harder to make
than the hyperbolic design.

The US Military and NASA did extensive reliability studies of crimped
versus soldered connection between connector pins or sockets and
stranded wire under heavy vibration. Crimped won hands down.

The solder-cup connectors were usually backfilled with polysulfide
rubber (which looks and smells like s**t, and sticks to everything
except teflon) to provide moisture sealing and strain relief.
Non-teflon wire would make a firm bond with polysulfide rubber.


Joe Gwinn

 

[bitrex]

On 8/11/2020 6:24 PM, Tim Williams wrote:

\"Phil Hobbs\" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:7023e4dd-38c1-165a-2aed-75078864178c@electrooptical.net...
I don\'t have any experience using potting, so I\'d be reluctant to use
it for this one.  We do have to use goop between the board and box to
keep
it from vibrating much.

Yeah, automotive does that a lot.  Not uncommon to see modules with
electrolytics sticking up from the muck.

Might do, then, to have just a little more, enough to cover where the
wires come out -- or put some extra goop around them?

And yeah, NASA doesn\'t like tinned wire either, indeed they have a whole
methodology for doing that correctly (which must be pretty inevitable
for the popularity of solder-cup MIL terminals?).  If they can do it,
it\'s definitely possible; whether it\'s worth following that procedure,
or maybe a watered-down version of it, is a potentially costly question
though.  Alas, I don\'t have that experience to offer...

Also a possibility, solder-in crimp termals.  Seen \'em on ATX PSUs
plenty of times.  Probably more of an assembly expedient than for
reliability though? (The crimp is basically just the barrel, no
socket/pin.  The barrel and wire is what goes into the board to get
soldered.  There\'s usually a retention tab, I assume to hold it in place
for wave soldering.)

I think in my example, the connections are all hand soldered.  Which has
to be a big adder to their assembly cost.  It\'s not mass production
quantities, and they don\'t seem to have much competition (and for an end
product that doesn\'t have much competition in turn), so I guess they
don\'t mind.  YMMV.

Oh also, I forget what they do with the IR sensors, if they\'re fully
potted, or partial, and if they have a seal around the optics.  Might be
the latter. Yet another thing to think about...


Mining is a very dirty business indeed.  I\'ve been down a few working
mines--underground, a mercury mine in BC (Pinchi Lake) and a gold mine
in the Northwest Territories (the Con) as well as an open pit lead/zinc
mine also in the NWT (Pine Point).  My Dad used to work for the old
Cominco [not the company currently trading under that name], and he
took me with him on a tour of their operations in the North.  It was
pretty cool--I was 12 at the time, and got to hold an 80-pound gold
bar.  (It was 75% gold and 25% silver iirc.)

Very cool.  Unless you were in one of those super deep mines that\'s over
40°C and full humidity, but other than that... :^)

They also like to wash down the trucks, and I mean using whatever is
handy: steam, seawater...  Electrolysis in connectors (even if they\'re
IP67) is sometimes a problem too.  At least you wouldn\'t have that
problem I guess.


Yeah, ours have an LPC845 Cortex M0+ in them.  Nice part--32 MHz, with
a gigantic pin mux so you can have almost any function on (almost) any
pin.


Ah, yep, cheap too.  Though I\'ve heard they\'re Microchip levels of
buggy. (Haven\'t looked at them in enough detail to know that myself.)

We use a ton of STM32s: affordable enough, easy to use (even supported
by Arduino, should you happen upon that route), not too many bugs.

Personally, I like AVR XMEGA, charming 8-bit machines, pricey though
they are.  Fortunately, as a hardware guy, I just play with them; I\'m in
no danger of putting one into production. :^)

Tim

Speaking of NASA, how did they do OPs task aboard spacecraft? High
vibration, check, low humidity, check, smoldering fire extremely serious
situation, check, so I\'m assuming they must have built a similar device...

 

[Robert Baer]

Phil Hobbs wrote:

On 2020-08-11 07:16, Tim Williams wrote:
A client has the same application but in rugged automotive conditions
(mining equipment, etc.).  They use a thermopile sensor.  (They\'re
detecting direct flame; sounds like your case needs more sensitivity,
so that probably wouldn\'t go, and explains the TIA, with, I guess, a
long wave photodiode or pyroelectric sensor.)

We have a visible channel, a SWIR channel (0.9-1.7 um), and a MWIR
channel (3-5 um).  The SWIR detector is 0.3 mm in diameter, so it needs
a very high-Z TIA.  (It uses two 100M resistors in series, shunted by a
series pair of very low leakage diodes so that it doesn\'t rail in bright
light.)


I forget what the minimum temperature is (maybe it was more or less
than your requirement?), but they use M-series Turck connectors
throughout. Pigtail type, leads soldered directly to the board.  Don\'t
remember what plastics they\'re made of or if they say, but they\'re
rated for the service in any case.  And as much potting as possible,
no direct route for moisture to get in.

I don\'t have any experience using potting, so I\'d be reluctant to use it
for this one.  We do have to use goop between the board and box to keep
it from vibrating much.

Mining is a very dirty business indeed.  I\'ve been down a few working
mines--underground, a mercury mine in BC (Pinchi Lake) and a gold mine
in the Northwest Territories (the Con) as well as an open pit lead/zinc
mine also in the NWT (Pine Point).  My Dad used to work for the old
Cominco [not the company currently trading under that name], and he took
me with him on a tour of their operations in the North.  It was pretty
cool--I was 12 at the time, and got to hold an 80-pound gold bar.  (It
was 75% gold and 25% silver iirc.)

They do have problems with vibration of connectors causing dropouts of
power or signal.  A recent change has been to put an MCU inside the
boxes, so instead of a DC signal, a serial keepalive message is sent,
and the system can be more aware of its integrity as well as more
forgiving of momentary dropout.

Yeah, ours have an LPC845 Cortex M0+ in them.  Nice part--32 MHz, with a
gigantic pin mux so you can have almost any function on (almost) any pin.

Not sure what you\'re showing with the rectangular header -- internal
board-to-board wiring?  External connections??

It\'s to go from the pigtailed M12 to the board.

We\'ve been going back and forth about soldering the wires directly to
the board, but have heard stories about vibration causing fatigue
failure at the stress concentration point where the tinned region ends,
* Have seen that many times over a 50 year period.

as well as anecdotal wisdom about the goodness of crimped connections in
environments like that.

* YES! MIL testing has shown that crimped connections are far more
reliable than soldered connections, due to fact of compression alloying
of wires.

Cheers

Phil Hobbs

 

[piglet]

Hi Phil, I have good results using the JST XA series which is the 2.5 mm version of what you propose. I use the latching clips and side entry pcb header as then a locating peg takes some stress off the through hole pins.

The non replaceable alternative is a solder pin or turret and then hand solder the wires to that and shrink sleeve the joint to absorb strain on the fragile portion where solder has wicked along the strands, but it ends up more work than using a connector.

piglet
(Using google groups on a phone while travelling in Africa)

 

[Phil Hobbs]

On 2020-08-14 05:19, piglet wrote:

Hi Phil, I have good results using the JST XA series which is the 2.5 mm version of what you propose. I use the latching clips and side entry pcb header as then a locating peg takes some stress off the through hole pins.

The non replaceable alternative is a solder pin or turret and then hand solder the wires to that and shrink sleeve the joint to absorb strain on the fragile portion where solder has wicked along the strands, but it ends up more work than using a connector.

piglet
(Using google groups on a phone while travelling in Africa)

Thanks. Have a good trip!

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