Today's Message Index:
----------------------
1. 04:31 AM - Re: For want of a nail . . . (FLYaDIVE)
2. 05:30 AM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (FLYaDIVE)
3. 06:00 AM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (Robert L. Nuckolls, III)
4. 06:26 AM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (William Daniell)
5. 09:24 AM - Re: Analog Volt Meter ()
6. 09:26 AM - Re: Analog Volt Meter (n1dw)
7. 10:09 AM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (Robert L. Nuckolls, III)
8. 10:11 AM - Re: Analog Volt Meter (The Kuffels)
9. 10:48 AM - Re: Analog Volt Meter (Charlie England)
10. 10:55 AM - Re: Analog Volt Meter (William Daniell)
11. 11:14 AM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (William Daniell)
12. 11:56 AM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (Robert L. Nuckolls, III)
13. 12:09 PM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (Robert L. Nuckolls, III)
14. 12:53 PM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (William Daniell)
15. 01:03 PM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (FLYaDIVE)
16. 04:22 PM - Re: Analog Volt Meter (Ernest Christley)
17. 08:02 PM - Re: Re: Is the OVP 5 A CB supposed to trip when I switch off the al (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: For want of a nail . . . |
Not at all Ernest;
Not that all "That's what see said," jokes are bad.
It's an engineering joke: How long is a Short?
As long as it takes the Technician to find it.
Its like a 'Knock - Knock" joke.
A knock - knock joke would not work without a door.
It's like "One Hand Clapping".
Barry
On Sun, May 27, 2018 at 10:21 PM, Ernest Christley <echristley@att.net>
wrote:
> I hope that is not a "that's what she said" joke.
>
>
> On Sunday, May 27, 2018 7:08 AM, FLYaDIVE <flyadive@gmail.com> wrote:
>
>
> How long is a Short?
>
> On Sat, May 26, 2018 at 11:49 AM, Robert L. Nuckolls, III <
> nuckolls.bob@aeroelectric.com> wrote:
>
> Spent too many hours and way too many dollars
> chasing gremlins from an antenna system only
> to discover that one of my SWR test coaxes
> had an INTERMITENT short. Made for some very
> confusing readings and misguided actions.
>
> Only accidently noticed that my anomalous readings
> manifested when coax behind the connector was
> subject to the right side-pressure. Swapped
> out the cable and the antenna refurbishment
> task moved forward after replacement of stuff
> that didn't need replacing.
>
> Tore down the connector and found a couple
> of 'whiskers' hanging out of the center
> pin crimp.
>
> [image: Emacs!]
>
> Just long enough to come within a few micro-inches
> of shorting the coax . . . putting the right
> force vector on the coax would close the gap.
>
> This was a commercially assembled test jumper
> that has been hanging on my cable rack for
> at least 15 years . . . just goes to show ya . . .
>
> Bob . . .
>
>
Message 2
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
Joe, Bob and Gaggle:
I'm perplexed!
I stood back, shook my head (Really, Physically - It is what I do to
restart the learning process). I TOTALLY agree with you on the diode
protecting the switch. The location of the Diode is NOT where I would put
it in the circuit IF it was ONLY for switch protection. As I said: Too
far away from the switch and what if it is the Ground that was being
switched?
My statements come from training way back in 1969. I used that training
and the Theory given to me from way back then and the outcome has given
correct results over many years.
I have always installed the diode to prevent 'Bounce Back' of the relay
contacts - NEVER - Thinking of the switch. LQQKs like my reasoning could
have been wrong, yet, I obtained good results.
Another thing I said was History Changes. We once only taught Electron
Theory, now we teach both electron and HOLE Theory. Why? Because it helps
better explain things.
Here is a link that takes the Physical Switch totally out of the circuit
YET the diode still exists in the circuit. It's (Diode, Alec) purpose is
to prevent Spikes.
My take on this is:
1 - Removing the spike is a good thing.
2 - Does not matter Why - You - Think the diode is there, it is the
function of the diode that makes the circuit work.
3 - Terminology - Constantly Changes. <-- I'm not happy with that!!!
Sometimes there are just too many shades of gray.
OK - So, take a look at this video.
https://www.youtube.com/watch?v=LXGtE3X2k7Y
Barry
On Sun, May 27, 2018 at 10:02 PM, Alec Myers <alec@alecmyers.com> wrote:
> I don't know what "it" you're referring to; I didn't have any specific
> circuit in mind.
>
> If you have an inductive load you can protect the relay contacts with a
> diode if you want to.
>
> Sent from my iPhone
>
> On May 27, 2018, at 9:49 PM, FLYaDIVE <flyadive@gmail.com> wrote:
>
> Alec:
>
> It is not directly protecting the contacts of the relay. The reverse EMF
> never touches the contacts of the relay. It is preventing the reverse EMF
> from allowing the contacts to bounce which causes the contacts to arc.
>
> Barry
>
> On Sun, May 27, 2018 at 8:31 PM, Alec Myers <alec@alecmyers.com> wrote:
>
>> If you want to protect the relay contacts from back EMF generated in an
>> inductive LOAD put a diode across the LOAD or across the relay contacts.
>> Either place will work.
>>
>> If you want to protect the switch from back EMF generated in the relay
>> COIL put a relay across the COIL or across the switch. Either place will
>> work.
>>
>>
>>
>> Sent from my iPhone
>>
>> On May 27, 2018, at 7:57 PM, FLYaDIVE <flyadive@gmail.com> wrote:
>>
>> Ken & Bob:
>>
>> If that was the case...
>> 1 - Then why place the diode on the relay and not on the switch?
>> After all, if it's an induced voltage the effects would decrease over the
>> running length of a wire, especially a straight wire.
>> 2 - In Bob's drawing the Switch is forward of the relay and controls the
>> Positive Voltage to the relay.
>> YET! Not all circuits with the same Diode and Relay switch the Positive
>> Voltage. Some put the switch on the Ground Leg of the relay.
>> 3 - When was this circuit and diode instillation designed?
>> I was taught this expiation way back in 1969. I have a feeling the
>> reasoning of the circuit was lost over decades of time. Yet, the good
>> intentions of the circuit remain. You always have to remember this has
>> always been called Electronics THEORY!
>> In the long run, you can't argue with success.
>>
>> Barry
>>
>>
>>
>> On Sun, May 27, 2018 at 6:14 PM, Ken Ryan <keninalaska@gmail.com> wrote:
>>
>>> Barry,
>>>
>>> I think that is at odds with the explanation offered by Bob, et al. If I
>>> understand them correctly, the diode does not protect the contacts of the
>>> relay, but rather the contacts of the switch that controls the relay.
>>>
>>> Ken
>>>
>>>
>>> On Sun, May 27, 2018 at 1:48 PM, FLYaDIVE <flyadive@gmail.com> wrote:
>>>
>>>> Joe & Bob:
>>>>
>>>> I was not able to link to the Z-16 schematic but if it is like what you
>>>> just posted Bob, the diode trick has been around for many years.
>>>> I'm sure there are different names for the way it is being used, the
>>>> name I know it by is: ANTI-BOUNCE DIODE.
>>>> Gaggle - If you look at the diode it is put in the REVERSE Polarity
>>>> Direction of the applied voltage.
>>>> Without the diode - When the power to the relay is removed, the
>>>> collapsing field of the relay produced an induced voltage in the opposite
>>>> direction as the energizing voltage. This voltage caused the relay contacts
>>>> to BOUNCE and not open the contacts as quickly or as definitively. This of
>>>> course caused excessive arcing of the contacts, shortening their life and
>>>> even welding the contacts closed and/or carbonizing the contacts.
>>>>
>>>> So, if the OV circuit is sensitive enough and fast enough it could
>>>> react to the induced spike.
>>>>
>>>> Barry
>>>>
>>>> On Sun, May 27, 2018 at 5:11 PM, Robert L. Nuckolls, III <
>>>> nuckolls.bob@aeroelectric.com> wrote:
>>>>
>>>>> At 02:37 PM 5/27/2018, you wrote:
>>>>>
>>>>> >
>>>>>
>>>>> Now all we have to do is figure out how the O.V. module tripped the
>>>>> circuit breaker with the switch open. The only thing that I can think of
>>>>> is that it happened during the time that an arc was jumping across the
>>>>> opening contacts.
>>>>>
>>>>>
>>>>> Oh . . . THAT diode. . . missed that part of the
>>>>> thread . . .
>>>>>
>>>>> <243745d4.jpg>
>>>>>
>>>>>
>>>>> Is that long enough to trip a breaker? Or maybe it is not wired like
>>>>> Z-16. Instead maybe the O.V. module is connected to the other side of the
>>>>> switch. The O.V. module will still function OK if it is.
>>>>> Anyway, glad it is working for you Will.
>>>>>
>>>>>
>>>>> I've seen this before . . . field collapse spikes
>>>>> on a beefy relay have been known to irritate the
>>>>> crowbar ovm. Had a Europa builder in Wichita having
>>>>> a similar problem with the avionics master relay
>>>>> in his EXP Bus system. Tacked a diode across the
>>>>> relay coil and order was restored in the universe.
>>>>>
>>>>>
>>>>> Bob . . .
>>>>>
>>>>
>>>>
>>>
>>
>
Message 3
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
At 08:49 PM 5/27/2018, you wrote:
>Alec:
>
>It is not directly protecting the contacts of
>the relay.=C2 The reverse EMF never touches the
>contacts of the relay.=C2 It is preventing the
>reverse EMF from allowing the contacts to bounce
>which causes the contacts to arc.
This is a myth . . . the coil collapse suppression
diode is demonstrably responsible for a DELAY in
the first opening of the relay's contacts . . .
but no significant effect on SPREADING VELOCITY
of those contacts. All other effects equal,
spreading velocity is a strong controlling factor
for arcing at the contacts during the opening
event.
Contacts bounce only on closing . . . which
is a strong factor along with inrush currents
that control tendencies to weld contacts
together. When we were exploring options for
controlling the landing gear pump motor, a
driving factor in relay/switch selection was
the closing the circuit on a very low static
resistance i.e. inrush probably on the order
of 100 Amps.
Bob . . .
Message 4
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
Bob,
curiously enough mine's a Europa too. Could it be something to do with
composites?
Another Symptom which might help the discussion. The CB tripped ONLY at
the moment of switching off the ALT. It could be reset immediately after
with no ill effects suggesting that it was something to do with the
switching off itself that caused the CB to trip.
By the way you all have completely lost me on the technical stuff - but I
am reading with interest,
Will
William Daniell
LONGPORT
+57 310 295 0744
On Mon, May 28, 2018 at 8:48 AM, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 08:49 PM 5/27/2018, you wrote:
>
> Alec:
>
> It is not directly protecting the contacts of the relay.=C3=82 The rever
se EMF
> never touches the contacts of the relay.=C3=82 It is preventing the reve
rse EMF
> from allowing the contacts to bounce which causes the contacts to arc.
>
>
> This is a myth . . . the coil collapse suppression
> diode is demonstrably responsible for a DELAY in
> the first opening of the relay's contacts . . .
> but no significant effect on SPREADING VELOCITY
> of those contacts. All other effects equal,
> spreading velocity is a strong controlling factor
> for arcing at the contacts during the opening
> event.
>
> Contacts bounce only on closing . . . which
> is a strong factor along with inrush currents
> that control tendencies to weld contacts
> together. When we were exploring options for
> controlling the landing gear pump motor, a
> driving factor in relay/switch selection was
> the closing the circuit on a very low static
> resistance i.e. inrush probably on the order
> of 100 Amps.
>
>
> Bob . . .
>
Message 5
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| Subject: | Analog Volt Meter |
Thanks for the link, but all the meters I can find on e-bay are at least 2
inches and I was looking for something smaller
Thanks
Mike
From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectr
ic-list-server@matronics.com] On Behalf Of Charlie England
Sent: May 27, 2018 9:30 PM
Subject: Re: AeroElectric-List: Analog Volt Meter
https://www.ebay.com/bhp/analog-panel-meter
Charlie
On May 27, 2018, at 10:47 PM, mike@vision499.com <mailto:mike@vision499.com
> wrote:
Does anybody know where I can get a small analog volt meter about the same
size as the UMA from aircraft spruce but at a better price?
http://www.aircraftspruce.ca/catalog/inpages/uma_instr9.php?clickkey=1320
0
Thanks
Mike
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Message 6
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| Subject: | Analog Volt Meter |
Google =98Westach voltmeter=99
From: owner-aeroelectric-list-server@matronics.com
<owner-aeroelectric-list-server@matronics.com> On Behalf Of
mike@vision499.com
Sent: Sunday, May 27, 2018 8:41 PM
Subject: AeroElectric-List: Analog Volt Meter
Does anybody know where I can get a small analog volt meter about the
same size as the UMA from aircraft spruce but at a better price?
http://www.aircraftspruce.ca/catalog/inpages/uma_instr9.php?clickkey=13
200
Thanks
Mike
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Message 7
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
>>If you want to protect the relay contacts from back EMF generated
>>in an inductive LOAD put a diode across the LOAD or across the
>>relay contacts. Either place will work.
Relay and switch contacts are almost never fitted
with prophylactics against wear-n-tear. When you
read design life specs for the various products
you virtually never see recommendations for adding
external devices intended to extend service life
of the contacts.
The reason being that any 'arc snubbing' device
must be tailored to the application . . . the
relay/switch manufacturer cannot anticipate hou
YOU will used the product . . . hence, they are
what they are and any failure to meed design
goals for service life generally involves a
feature in the application that is out in left
field . . . a once in a million encounter with
the immutable laws of physics.
Good case in point was the rash of relay failures
we experienced in the B400 that took a couple years
to track down . . . and the relay manufacturer's
had no clue . . . hence not helpful.
https://goo.gl/QcfSYo
I've designed perhaps 4-5 products wherein it
was useful to add arc suppression directly
to contacts. The most recent being an OV
relay addition to a specific airplane with a generator
where the arc suppression was 'tuned' to
generator field inductance.
http://www.aeroelectric.com/Pictures/Relays/Relay_with_Arc_Supp
But for the most part, relays as switches are
selected to task with no adjuncts intended to
enhance service life.
Diodes and other solid state devices generally
serve no useful purpose across the contacts
of a switch. The Ceaans/FAA got caught with their
pants down around their ankles on the Great
ACS-Gerdes, OFF-L-R-Both-Start Keyswitch fiasco
circa 1990.
I captured the corrected documents here
https://goo.gl/QV3gTF
The first issue of these documents placed the
diode across the starter control switch contacts
in the ACS keyswitch assembly . . . only to
discover that the diode had no benefit. The
physics is described in the second page of
https://goo.gl/WUS1Ya
Bob . . .
Message 8
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| Subject: | Re: Analog Volt Meter |
Mike,
<< small analog volt meter about the same size as the UMA from aircraft sp
ruce but at a better price? >>
If you can stand an industrial look instead of an aircraft look, Mouser Ele
ctronics 529-17843 is a Simpson 1.5 inch square 0-15 volt meter for $96. 1
=2E15 and 2.5 inch meters are about the same price.
Tom Kuffel
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Message 9
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| Subject: | Re: Analog Volt Meter |
On 5/28/2018 12:11 PM, The Kuffels wrote:
> Mike,
> <<small analog volt meter about the same size as the UMA from
> aircraft spruce but at a better price? >>
> If you can stand an industrial look instead of an aircraft look,
> Mouser Electronics 529-17843 is a Simpson 1.5 inch square 0-15 volt
> meter for $96. 1.15 and 2.5 inch meters are about the same price.
> Tom Kuffel
>
And if you can give up the analog requirement (and gain a lot of
accuracy), there are many digital options with under $20 price points.
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Message 10
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| Subject: | Re: Analog Volt Meter |
I bought a hall effect ammeter combined with a voltmeter from Amazon for
USD24. It's digital. Its readings are the same as my Dynon which was a
tad more expensive.
Will
William Daniell
LONGPORT
+57 310 295 0744
On Mon, May 28, 2018 at 12:48 PM, Charlie England <ceengland7@gmail.com>
wrote:
> On 5/28/2018 12:11 PM, The Kuffels wrote:
>
> Mike,
>
> << small analog volt meter about the same size as the UMA from aircraft
> spruce but at a better price? >>
>
> If you can stand an industrial look instead of an aircraft look, Mouser
> Electronics 529-17843 is a Simpson 1.5 inch square 0-15 volt meter for
> $96. 1.15 and 2.5 inch meters are about the same price.
>
> Tom Kuffel
>
> And if you can give up the analog requirement (and gain a lot of
> accuracy), there are many digital options with under $20 price points.
>
>
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Message 11
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
Joe
the OVP is on the downstream side of the switch that is to say on the
Relay side of the swtich.
Will
William Daniell
LONGPORT
+57 310 295 0744
On Sun, May 27, 2018 at 7:59 PM, user9253 <fransew@gmail.com> wrote:
>
> An arc suppression diode needs to be connected in parallel with the
> inductor with the banded end of the diode connected to positive. The ideal
> physical location of the diode is as close to the coil as practical.
> However, the diode could be located at the switch that turns the coil on
> and off. Even so, the diode still needs to be connected in parallel with
> the coil. A diode will limit induced voltage to about 1 volt, which is the
> forward voltage drop of the diode. The main purpose of an arc suppression
> diode is to protect the controlling switch contacts from arcing. Below is
> a picture of a diode located at the switch. Notice that even though the
> diode is located remote from the contactor coil, it is still connected in
> parallel with the coil. The banded end of the diode connects to the
> positive side of the coil, and the other end of the diode is connected to
> the negative side of the coil (through ground). Connecting a diode across
> switch contacts does little good.
>
> --------
> Joe Gores
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=480463#480463
>
>
> Attachments:
>
> http://forums.matronics.com//files/diode_arc_suppression_166.jpg
>
>
Message 12
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
At 07:29 AM 5/28/2018, you wrote:
>Joe, Bob and Gaggle:
>
>I'm perplexed!
>I stood back, shook my head (Really, Physically
>- It is what I do to restart the learning
>process).=C2 I TOTALLY agree with you on the diode protecting the switch.
That's ONE feature of the field collapse
suppression diode. It may keep the EFIS
display from 'glitching', the ov module
from nuisance tripping, eliminate a 'click'
in the headphones . . . and yes . . . extend
the service life of a switch.
>The location of the Diode is NOT where I would put it in
>the circuit IF it was ONLY for switch protection.
It's never is the only reason . . .
> As I said: Too far away from the switch and what if
> it is the Ground that was being switched?
Neither of these conditions matter. . .
I cannot speak to your training/experience. I can
speak to my experience and demonstrations on
the bench and in airplanes with observations
made, measurements taken, deductions proposed
and documents published with invitations
for good skeptical/critical review.
If you find fault with anything I've published
or referenced . . . that's the place to start.
Nobody is more interested in correcting faulty
information and/or clarifying an explanation
as I am.
If you have an experiment you'd like to see
conducted, give us a bill of materials, schematic,
your hypothesis for outcome and instructions
for conducting the experiment. I'll set it up on
the bench and publish the results.
Bob . . .
Message 13
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
At 08:24 AM 5/28/2018, you wrote:
>Bob,
>
>curiously enough mine's a Europa too.=C2 Could it
>be something to do with composites?
no . . it would have happened in an RV too
>Another Symptom which might help the
>discussion.=C2 The CB tripped ONLY at the moment
>of switching off the ALT.=C2 It could be reset
>immediately after with no ill effects suggesting
>that it was something to do with the switching
>off itself that caused the CB to trip.
Yup . . . that's how the transient event is
created.
Emacs!
When the controlling switch opens, the magnetic field
in the relay collapse very rapidly (~3 milliSeconds
in the plot above).
>By the way you all have completely lost me on
>the technical stuff - but I am reading with interest,
No problem . . . that's what the List is for. Advise
and explain. The level of understanding achieved
needs only to offer some level of confidence that
nobody is going to blow smoke blown up your pant leg
here . . .
Bob . . .
Message 14
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
This stuff is very cool.
William Daniell
LONGPORT
+57 310 295 0744
On Mon, May 28, 2018 at 2:08 PM, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 08:24 AM 5/28/2018, you wrote:
>
> Bob,
>
> curiously enough mine's a Europa too.=C3=82 Could it be something to do
with
> composites?
>
>
> no . . it would have happened in an RV too
>
>
> Another Symptom which might help the discussion.=C3=82 The CB tripped ON
LY at
> the moment of switching off the ALT.=C3=82 It could be reset immediately
after
> with no ill effects suggesting that it was something to do with the
> switching off itself that caused the CB to trip.
>
>
> Yup . . . that's how the transient event is
> created.
>
> [image: Emacs!]
>
> When the controlling switch opens, the magnetic field
> in the relay collapse very rapidly (~3 milliSeconds
> in the plot above).
>
>
> By the way you all have completely lost me on the technical stuff - but I
> am reading with interest,
>
>
> No problem . . . that's what the List is for. Advise
> and explain. The level of understanding achieved
> needs only to offer some level of confidence that
> nobody is going to blow smoke blown up your pant leg
> here . . .
>
>
> Bob . . .
>
Message 15
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
Bob:
With the screen shot of the O scope...
What signal did you use to trigger the scope (capture the screen shot)?
The 'M'... Is that for Manual Mode?
Where do you have the leads attached?
Where are you measuring the ~3 ms from & to?
What is your definition of: "Fire across contacts" and Fire goes out here"?
Barry
>
> [image: Emacs!]
>
>
Message 16
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| Subject: | Re: Analog Volt Meter |
Marlin Jones has a good selection:
Panel Meters & Meter Shunts | MPJA.COM
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Panel Meters & Meter Shunts | MPJA.COM
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On Sunday, May 27, 2018 11:44 PM, "mike@vision499.com" <mike@vision499.
com> wrote:
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0, #yiv2610340628 li.yiv2610340628msonormal0, #yiv2610340628 div.yiv2610340
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oes anybody know where I can get a small analog volt meter about the same s
ize as the UMA from aircraft spruce but at a better price?=C2-=C2-=C2
-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-
http://www.aircraftspruce.ca/catalog/inpages/uma_instr9.php?clickkey=132
00 =C2-Thanks =C2-Mike =C2- =C2- =C2- =C2- =C2-
| | Virus-free. www.avast.com |
Message 17
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| Subject: | Re: Is the OVP 5 A CB supposed to trip when I |
switch off the al
At 03:03 PM 5/28/2018, you wrote:
>Bob:
>
>With the screen shot of the O scope...=C2 =C2
>What signal did you use to trigger the scope (capture the screen shot)?
>The 'M'...=C2 Is that for Manual Mode?
>Where do you have the leads attached?
>Where are you measuring the ~3 ms from & to?
>What is your definition of: "Fire across contacts" and Fire goes out here"?
Referring to the article at:
https://goo.gl/WUS1Ya
The first figure is the performance baseline for
the contactor . . . a Stancor/White-Rogers 70
series, 12v, 'whisky-barrel'.
[]
One terminal of the coil is grounded. The other
terminal gets 12vdc applied through a switch.
The scope Ch1 reads votlage across the coil.
Trigger is ac coupled for a negative going
excursion of the coil voltage (initiated by
first opening of the controlling switch). Yes,
"M" is for manual mode (single sweep with manual
reset for next trigger). Using the 4th trace
from the article we see that the first major
event (the field collapse transient) begins
at the trigger point (little black arrow at top)
and is pretty much over 6 major horizontal
divisions at 0.5mS per division.
>Emacs!
>
The first figure of the article is the baseline coil
collapse signature for that contactor. For this
measurement, I needed a switch with a VERY fast contact
spreading velocity. As the article states, this was
achieved with a piece of 22awg wire strung between to
c-clamps and tensioned with a bunch of rubber bands.
The switch was 'opened' by simply cutting the wire.
You will note that dv/dt (slope) for Emf during field-collapse
is on the order of 1v/microSecond. The transient's amplitude
exceeds 300 Volts.
The last figure, repeated above, explores the collapse
signature when coil current is controlled by an ordinary
toggle switch. Here again we see a sharp, negative-going
transient that begins with switch opening is 0.05v/microSecond
or 1/20th that of the coil when controlled with a fast switch.
The ONLY explanation for this difference is that as the switch
contacts first opened, coil collapse begins and an arc forms
in the gap. This prevents coil current from going to zero
and produces a t=L/R retardation of collapse. ~1250 uS
after switch opening, we see a transient that marks an increase
in the slope of the curve . . . this has to be where the fire
goes out and the DC current flow in the coil goes zero.
The narrative accompanying the other two figures is, I
believe, self explanatory.
This particular study focuses on arcing at the controlling
switch and does not address arcing at the contacts of the
contactor as driven by contact spreading velocity. That's
another article.
Bob . . .
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