Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss
CM Chokes sometimes suck
83 views
Skip to first unread message
Harry D
May 21, 2013, 11:45:08 AM5/21/13
to
I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
What is my best arugment to have them replaced with a short?
Harry
What is my best arugment to have them replaced with a short?
Harry
Jim Thompson
May 21, 2013, 12:05:11 PM5/21/13
to
contracting at Honeywell... told the management, "I won't sign that.
If you think that's right, _you_ sign it."
They never signed off on anything I balked at ;-)
And every time I offered to quit, they declined to accept my offer.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
tm
May 21, 2013, 12:08:24 PM5/21/13
to
"Harry D" <har...@tdsystems.org> wrote in message
news:76bdb327-0696-413d...@googlegroups.com...
Cost?
If it's for the government, then that won't work.
John Larkin
May 21, 2013, 12:15:21 PM5/21/13
to
just ignore them. Ignoring is better, because by the time the stuff is shipped,
it's too late to change it, too late to argue, and it works, too.
I have one customer who insists that every mounting hole of a PCB be not
connected to the ground plane. Then they insist on a parallel RC from each
mounting hole to the ground plane. I ignore them.
A lot of EMI and grounding gurus are idiots. Like that HoJo guy.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Joerg
May 21, 2013, 12:17:24 PM5/21/13
to
Jim Thompson wrote:
> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
> <har...@tdsystems.org> wrote:
>
>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>> What is my best arugment to have them replaced with a short?
>>
>> Harry
>
Hmm, for some reason I can't see the original post.
> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
> <har...@tdsystems.org> wrote:
>
>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>> What is my best arugment to have them replaced with a short?
>>
>> Harry
>
> Refuse to sign off on it. I did that numerous times when I was
> contracting at Honeywell... told the management, "I won't sign that.
> If you think that's right, _you_ sign it."
>
fuselage as ground return. Personally I do not like that but t'is the
way they are often built. When the box gets bolted to the fuselage and
the other side of the GND path of a CM choke is also connected to the
fuselage (where else could it go?) then that essentially shorts out the
CM choke. Makes it largely inefficient.
[...]
--
Regards, Joerg
http://www.analogconsultants.com/
Nico Coesel
May 21, 2013, 12:19:23 PM5/21/13
to
Harry D <har...@tdsystems.org> wrote:
> I'm working with a group designing avionics equipment and they recently hi=
>red an EMI guru. He insists on placing CM chokes on every single ended I/O =
>signal line. These signals can be floating 100K thermistors that are receiv=
>ed by a Pi filter (100K resistor and two 1.0uF caps to ground). The minitur=
connector then the CM chokes won't add anything. But if there is some
length of PCB trace between the Pi filter and the connector then it is
wise to use an extra filter. PCB traces tend to pick up all kinds of
noise and that noise can be transferred into a connector if there is
no filtering at the connector.
--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------
> I'm working with a group designing avionics equipment and they recently hi=
>red an EMI guru. He insists on placing CM chokes on every single ended I/O =
>signal line. These signals can be floating 100K thermistors that are receiv=
>ed by a Pi filter (100K resistor and two 1.0uF caps to ground). The minitur=
>e CM chokes are 1k at 100MHz (1.6uH).
> What is my best arugment to have them replaced with a short?
It depends where the Pi filter is located. If it is close to the
> What is my best arugment to have them replaced with a short?
connector then the CM chokes won't add anything. But if there is some
length of PCB trace between the Pi filter and the connector then it is
wise to use an extra filter. PCB traces tend to pick up all kinds of
noise and that noise can be transferred into a connector if there is
no filtering at the connector.
--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------
John Larkin
May 21, 2013, 12:24:10 PM5/21/13
to
On Tue, 21 May 2013 09:17:24 -0700, Joerg <inv...@invalid.invalid> wrote:
>Jim Thompson wrote:
>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>> <har...@tdsystems.org> wrote:
>>
>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>> What is my best arugment to have them replaced with a short?
>>>
>>> Harry
>>
>
>Hmm, for some reason I can't see the original post.
>
>
>> Refuse to sign off on it. I did that numerous times when I was
>> contracting at Honeywell... told the management, "I won't sign that.
>> If you think that's right, _you_ sign it."
>>
>
>One of the peculiarities in aircraft designs is that they often use the
>fuselage as ground return. Personally I do not like that but t'is the
>way they are often built.
I think it's great. The only way you can lose low-impedance ground continuity is
>Jim Thompson wrote:
>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>> <har...@tdsystems.org> wrote:
>>
>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>> What is my best arugment to have them replaced with a short?
>>>
>>> Harry
>>
>
>Hmm, for some reason I can't see the original post.
>
>
>> Refuse to sign off on it. I did that numerous times when I was
>> contracting at Honeywell... told the management, "I won't sign that.
>> If you think that's right, _you_ sign it."
>>
>
>One of the peculiarities in aircraft designs is that they often use the
>fuselage as ground return. Personally I do not like that but t'is the
>way they are often built.
if the airframe is ripped into pieces.
Well, unless it's made of composites. I wonder how they handle that.
John Larkin
May 21, 2013, 12:28:55 PM5/21/13
to
On Tue, 21 May 2013 16:19:23 GMT, ni...@puntnl.niks (Nico Coesel) wrote:
>Harry D <har...@tdsystems.org> wrote:
>
>> I'm working with a group designing avionics equipment and they recently hi=
>>red an EMI guru. He insists on placing CM chokes on every single ended I/O =
>>signal line. These signals can be floating 100K thermistors that are receiv=
>>ed by a Pi filter (100K resistor and two 1.0uF caps to ground). The minitur=
>>e CM chokes are 1k at 100MHz (1.6uH).
>> What is my best arugment to have them replaced with a short?
>
>It depends where the Pi filter is located. If it is close to the
>connector then the CM chokes won't add anything. But if there is some
>length of PCB trace between the Pi filter and the connector then it is
>wise to use an extra filter. PCB traces tend to pick up all kinds of
>noise and that noise can be transferred into a connector if there is
>no filtering at the connector.
On a signal pin, I usually put a resistor or a ferrite bead first, near the
>Harry D <har...@tdsystems.org> wrote:
>
>> I'm working with a group designing avionics equipment and they recently hi=
>>red an EMI guru. He insists on placing CM chokes on every single ended I/O =
>>signal line. These signals can be floating 100K thermistors that are receiv=
>>ed by a Pi filter (100K resistor and two 1.0uF caps to ground). The minitur=
>>e CM chokes are 1k at 100MHz (1.6uH).
>> What is my best arugment to have them replaced with a short?
>
>It depends where the Pi filter is located. If it is close to the
>connector then the CM chokes won't add anything. But if there is some
>length of PCB trace between the Pi filter and the connector then it is
>wise to use an extra filter. PCB traces tend to pick up all kinds of
>noise and that noise can be transferred into a connector if there is
>no filtering at the connector.
connector pin. That keeps RF current from being pushed into the circuit traces.
CM chokes don't help much to attenuate differential noise, and one shouldn't
assume that the outside world is thoughtful enough to provide only differential
EMI.
Joerg
May 21, 2013, 12:39:12 PM5/21/13
to
John Larkin wrote:
> On Tue, 21 May 2013 09:17:24 -0700, Joerg <inv...@invalid.invalid> wrote:
>
>> Jim Thompson wrote:
>>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>>> <har...@tdsystems.org> wrote:
>>>
>>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>>> What is my best arugment to have them replaced with a short?
>>>>
>>>> Harry
>> Hmm, for some reason I can't see the original post.
>>
>>
>>> Refuse to sign off on it. I did that numerous times when I was
>>> contracting at Honeywell... told the management, "I won't sign that.
>>> If you think that's right, _you_ sign it."
>>>
>> One of the peculiarities in aircraft designs is that they often use the
>> fuselage as ground return. Personally I do not like that but t'is the
>> way they are often built.
>
> I think it's great. The only way you can lose low-impedance ground continuity is
> if the airframe is ripped into pieces.
>
Our power went in the middle of writing this, Hurumph.
> On Tue, 21 May 2013 09:17:24 -0700, Joerg <inv...@invalid.invalid> wrote:
>
>> Jim Thompson wrote:
>>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>>> <har...@tdsystems.org> wrote:
>>>
>>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>>> What is my best arugment to have them replaced with a short?
>>>>
>>>> Harry
>> Hmm, for some reason I can't see the original post.
>>
>>
>>> Refuse to sign off on it. I did that numerous times when I was
>>> contracting at Honeywell... told the management, "I won't sign that.
>>> If you think that's right, _you_ sign it."
>>>
>> One of the peculiarities in aircraft designs is that they often use the
>> fuselage as ground return. Personally I do not like that but t'is the
>> way they are often built.
>
> I think it's great. The only way you can lose low-impedance ground continuity is
> if the airframe is ripped into pieces.
>
Current takes all paths, not just the one of least resistance. So if
anything in the path rattles loose a bit because of old rivets,
corrosion or whatever, you can have a bzzzt-phsssst situation. Those can
turn into a problem at 45,000ft. It's the same in a car but there you
can simply pull over if something smokes. And even then people can die
as we have recently seen on the Bay Bridge when the back of a limousine
caught fire :-(
> Well, unless it's made of composites. I wonder how they handle that.
>
George Herold
May 21, 2013, 12:50:21 PM5/21/13
to
other half of the common mode choke attached to? Is the other half
just grounded at both ends? So it's just like an inductor in series
with the signal line? Is it wound on a toroid? (If not it could add
more EMI to the signal.)
I've 'spent' hours collecting data showing that someone's 'assumption'
just wasn't true. It seems like a waste of time, but it keeps the
project moving forward.
George H.
Joerg
May 21, 2013, 12:54:50 PM5/21/13
to
George Herold wrote:
> On May 21, 11:45 am, Harry D <har...@tdsystems.org> wrote:
>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>> What is my best arugment to have them replaced with a short?
>>
>> Harry
>
> Sorry, I don't understand. If it's a single ended line, what's the
> other half of the common mode choke attached to? Is the other half
> just grounded at both ends? So it's just like an inductor in series
> with the signal line? Is it wound on a toroid? (If not it could add
> more EMI to the signal.)
>
It's worse than that. If you connect both ends of one winding of a CM
> On May 21, 11:45 am, Harry D <har...@tdsystems.org> wrote:
>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>> What is my best arugment to have them replaced with a short?
>>
>> Harry
>
> Sorry, I don't understand. If it's a single ended line, what's the
> other half of the common mode choke attached to? Is the other half
> just grounded at both ends? So it's just like an inductor in series
> with the signal line? Is it wound on a toroid? (If not it could add
> more EMI to the signal.)
>
choke to the same ground then it behaves like a shorted transformer. The
only inductance left to fight EMI will be its leakage inductance.
[...]
George Herold
May 21, 2013, 1:07:51 PM5/21/13
to
transformers.
Well if that's how Harry's CM choke is hooked up then at least it's
not doing any harm.
George H.
Harry D
May 21, 2013, 1:16:18 PM5/21/13
to
Harry D
May 21, 2013, 1:16:52 PM5/21/13
to
On Tuesday, May 21, 2013 9:50:21 AM UTC-7, George Herold wrote:
Sorry George when I stated "single ended input line". There is a floating thermistor in a motor winding that could be a double ended input with the CM choke and Pi filter or single ended into the Pi filter. I'm stating that the added CM choke adds nothing.
Thanks,
Harry
Thanks,
Harry
Tim Wescott
May 21, 2013, 1:17:46 PM5/21/13
to
pick it off of one point and just use that one point, even if you need
long wires.
Or you need to find a Really Good way of sending your sensitive signals
in a common-mode resistant sort of way.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Joerg
May 21, 2013, 1:27:41 PM5/21/13
to
A CM choke can be beneficial in such situations but only if the
thermistor would deliver a signal with higher frequency spectral
content. Which thermistors generally don't. So you might as well just
RC-lowpass the heck out of it.
If it was a fast magnetic pickup or something I would consider a CM choke.
John Larkin
May 21, 2013, 1:57:24 PM5/21/13
to
different values of bypass cap on every power pin. It works, so keep
doing it.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
John Larkin
May 21, 2013, 1:59:04 PM5/21/13
to
the other wire go?
Joerg
May 21, 2013, 2:23:11 PM5/21/13
to
John Larkin wrote:
> On Tue, 21 May 2013 10:07:51 -0700 (PDT), George Herold
> <ghe...@teachspin.com> wrote:
>
>> On May 21, 12:54 pm, Joerg <inva...@invalid.invalid> wrote:
>>> George Herold wrote:
>>>> On May 21, 11:45 am, Harry D <har...@tdsystems.org> wrote:
>>>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>>>> What is my best arugment to have them replaced with a short?
>>>>> Harry
>>>> Sorry, I don't understand. If it's a single ended line, what's the
>>>> other half of the common mode choke attached to? Is the other half
>>>> just grounded at both ends? So it's just like an inductor in series
>>>> with the signal line? Is it wound on a toroid? (If not it could add
>>>> more EMI to the signal.)
>>> It's worse than that. If you connect both ends of one winding of a CM
>>> choke to the same ground then it behaves like a shorted transformer. The
>>> only inductance left to fight EMI will be its leakage inductance.
>> Hmm, Scratch scratch... OK I've got no 'intuitive' feel for
>> transformers.
>> Well if that's how Harry's CM choke is hooked up then at least it's
>> not doing any harm.
>>
>
> It's like wearing garlic to keep vampires away. ...
> On Tue, 21 May 2013 10:07:51 -0700 (PDT), George Herold
> <ghe...@teachspin.com> wrote:
>
>> On May 21, 12:54 pm, Joerg <inva...@invalid.invalid> wrote:
>>> George Herold wrote:
>>>> On May 21, 11:45 am, Harry D <har...@tdsystems.org> wrote:
>>>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>>>> What is my best arugment to have them replaced with a short?
>>>>> Harry
>>>> Sorry, I don't understand. If it's a single ended line, what's the
>>>> other half of the common mode choke attached to? Is the other half
>>>> just grounded at both ends? So it's just like an inductor in series
>>>> with the signal line? Is it wound on a toroid? (If not it could add
>>>> more EMI to the signal.)
>>> It's worse than that. If you connect both ends of one winding of a CM
>>> choke to the same ground then it behaves like a shorted transformer. The
>>> only inductance left to fight EMI will be its leakage inductance.
>> Hmm, Scratch scratch... OK I've got no 'intuitive' feel for
>> transformers.
>> Well if that's how Harry's CM choke is hooked up then at least it's
>> not doing any harm.
>>
>
When working in Korea they told me that one day of not ingesting any
garlic can easily shorten my life by a month. When I came back my wife
almost banned me from the bedroom because I reeked of garlic so bad.
> ... Or paralleling three
> different values of bypass cap on every power pin. It works, so keep
> doing it.
>
Or growling at approaching clouds. Our Rottweiler did that when he was
> doing it.
>
young. Made the clouds go away, worked every single time, so ...
Phil Hobbs
May 21, 2013, 2:33:51 PM5/21/13
to
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Mark
May 21, 2013, 2:58:27 PM5/21/13
to
it's a team effort, you really have no choice now but to leave the CM
chokes in because..
if you convince the EMI guru to take them out now ,,,, and in the
future, there is ANY kind of an EMI issue, it will be YOUR fault.
If they don't hurt anything, leave them in and move on.
Mark
chokes in because..
if you convince the EMI guru to take them out now ,,,, and in the
future, there is ANY kind of an EMI issue, it will be YOUR fault.
If they don't hurt anything, leave them in and move on.
Mark
Harry D
May 21, 2013, 3:25:36 PM5/21/13
to
On Tuesday, May 21, 2013 10:59:04 AM UTC-7, John Larkin wrote:
> On Tue, 21 May 2013 10:16:52 -0700 (PDT), Harry D
>
> On Tue, 21 May 2013 10:16:52 -0700 (PDT), Harry D
>
But you knew that already.
Cheers, Harry
Harry D
May 21, 2013, 3:30:18 PM5/21/13
to
John Larkin
May 21, 2013, 4:23:56 PM5/21/13
to
Tauno Voipio
May 21, 2013, 5:08:55 PM5/21/13
to
On 21.5.13 7:24 , John Larkin wrote:
> On Tue, 21 May 2013 09:17:24 -0700, Joerg <inv...@invalid.invalid> wrote:
>
>> Jim Thompson wrote:
>>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>>> <har...@tdsystems.org> wrote:
>>>
>>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>>> What is my best arugment to have them replaced with a short?
>>>>
>>>> Harry
>>>
>>
>> Hmm, for some reason I can't see the original post.
>>
>>
>>> Refuse to sign off on it. I did that numerous times when I was
>>> contracting at Honeywell... told the management, "I won't sign that.
>>> If you think that's right, _you_ sign it."
>>>
>>
>> One of the peculiarities in aircraft designs is that they often use the
>> fuselage as ground return. Personally I do not like that but t'is the
>> way they are often built.
>
> I think it's great. The only way you can lose low-impedance ground continuity is
> if the airframe is ripped into pieces.
>
> Well, unless it's made of composites. I wonder how they handle that.
>
>
There are return lines, at least in my DA42 (you can Google for the type).
> On Tue, 21 May 2013 09:17:24 -0700, Joerg <inv...@invalid.invalid> wrote:
>
>> Jim Thompson wrote:
>>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>>> <har...@tdsystems.org> wrote:
>>>
>>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>>> What is my best arugment to have them replaced with a short?
>>>>
>>>> Harry
>>>
>>
>> Hmm, for some reason I can't see the original post.
>>
>>
>>> Refuse to sign off on it. I did that numerous times when I was
>>> contracting at Honeywell... told the management, "I won't sign that.
>>> If you think that's right, _you_ sign it."
>>>
>>
>> One of the peculiarities in aircraft designs is that they often use the
>> fuselage as ground return. Personally I do not like that but t'is the
>> way they are often built.
>
> I think it's great. The only way you can lose low-impedance ground continuity is
> if the airframe is ripped into pieces.
>
> Well, unless it's made of composites. I wonder how they handle that.
>
>
--
Tauno Voipio
Spehro Pefhany
May 21, 2013, 5:14:02 PM5/21/13
to
said for not bringing out antennas connected solidly to various points
on the internal ground plane(s). If there's a Pi filter as you
describe on the "ground" line too, then it doesn't matter.
For something like a thermistor, there's no reason I can think of not
to use pennies-a-piece tiny ferrite beads. You only need a CM choke
when the current is high enough to saturate an inductor.
John Larkin
May 21, 2013, 5:25:31 PM5/21/13
to
On Tue, 21 May 2013 17:14:02 -0400, Spehro Pefhany
<spef...@interlogDOTyou.knowwhat> wrote:
>On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
><har...@tdsystems.org> wrote:
>
>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>> What is my best arugment to have them replaced with a short?
>>
>> Harry
>
>Maybe I'll be shat upon for this, but IMHO, there's something to be
>said for not bringing out antennas connected solidly to various points
>on the internal ground plane(s). If there's a Pi filter as you
>describe on the "ground" line too, then it doesn't matter.
If the pcb ground plane is solidly bolted to the box, and especially
<spef...@interlogDOTyou.knowwhat> wrote:
>On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
><har...@tdsystems.org> wrote:
>
>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>> What is my best arugment to have them replaced with a short?
>>
>> Harry
>
>Maybe I'll be shat upon for this, but IMHO, there's something to be
>said for not bringing out antennas connected solidly to various points
>on the internal ground plane(s). If there's a Pi filter as you
>describe on the "ground" line too, then it doesn't matter.
if the connector shells are bolted to the box and to the PCB ground
plane, bringing in a ground through a connector pin won't cause EMI
problems.
>
>For something like a thermistor, there's no reason I can think of not
>to use pennies-a-piece tiny ferrite beads. You only need a CM choke
>when the current is high enough to saturate an inductor.
>
EMI rectification errors then to be in the 100+ MHz range, and tend to
follow PCB resonances, both broken up by a bead. A common-mode choke
only attenuates... common mode RF! But grounding one pin, and RC
filtering the other, will usually work fine.
A 100K thermistor in a motor winding does get interesting, especially
if there's a high-frequency motor driver.
John Miles, KE5FX
May 22, 2013, 3:47:21 AM5/22/13
to
On May 21, 8:45 am, Harry D <har...@tdsystems.org> wrote:
> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
> What is my best arugment to have them replaced with a short?
>
> Harry
By "single ended" do you mean separate signal and ground conductors,
> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
> What is my best arugment to have them replaced with a short?
>
> Harry
or a signal whose ground return is the airframe or something else
besides another wire routed next to the signal line? I understand
that you aren't referring to a differential line, but "single ended"
by itself doesn't say anything about the ground return.
What is the expected offending signal that the EMI guru is trying to
filter out?
How's your 1.0 uF capacitor look at, say, 120 MHz? For that matter,
how does your 100K resistor look?
-- john
Fred Bartoli
May 22, 2013, 8:06:00 AM5/22/13
to
And to justify suckers the high expense, EMI experts count power ratios
in Nipper as we all know.
--
Thanks,
Fred.
Phil Hobbs
May 22, 2013, 9:55:25 AM5/22/13
to
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
+1 845 480 2058
Harry D
May 22, 2013, 10:56:46 AM5/22/13
to
The thermistor comes into the PCB in a shielded twisted pair. One lead goes directly to ground, the other thru a Pi filter (220nF, 100K, 220nf) to a Hi Z ADC input. The caps are X7R. The signal BW < 1.0Hz. The noise bandwidth is >10 MHz but the Pi filter has a BW of <7Hz. Now you want to place your stinkin bead where?
Regards, Harry
John Larkin
May 22, 2013, 12:02:56 PM5/22/13
to
This is a thermocouple input, and it's heavily lowpass filtered by RCs, and then
by software filtering. The tc cable is a shielded pair. Unfortunately, the tc is
inside an NMR probe, along with high field levels of RF in the 50-500 MHz range.
The RF did (always will) get into the signal conditioning opamps and get
rectified to small offsets, in a system where 1 microvolt matters. I added this
bead
https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/Bead_L900.JPG
and it helped by something like 30 dB, and especially broke up narrowband
resonances.
I got this business by doing this better than their previous vendor. An RF
generator could shut down his controller from clear across the room. I've sold
over 3000 controllers so far, not bad for a "stinkin bead."
--
John Larkin Highland Technology Inc
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
Fred Bartoli
May 22, 2013, 12:21:35 PM5/22/13
to
Le Wed, 22 May 2013 09:55:25 -0400, Phil Hobbs a écrit:
> Fred Bartoli wrote:
>>
>> Le Tue, 21 May 2013 12:30:18 -0700, Harry D a écrit:
> Fred Bartoli wrote:
>>
>>
>> > On Tuesday, May 21, 2013 11:58:27 AM UTC-7, Mark wrote:
>> >> it's a team effort, you really have no choice now but to leave the
>> >> CM
>> >>
>> >> chokes in because..
>> >>
>> >>
>> >>
>> >> if you convince the EMI guru to take them out now ,,,, and in the
>> >>
>> >> future, there is ANY kind of an EMI issue, it will be YOUR fault.
>> >>
>> >>
>> >>
>> >> If they don't hurt anything, leave them in and move on.
>> >>
>> >>
>> >>
>> >> Mark
>> >
>> > Mark, you make a good point but this guru will rain on my parade
>> > forever and that s$it must stop. He also gets paid a lot more than
>> > me and that PMO!!
>>
>> Hey, EMI wasn't Master's Voice for no reason.
>> And to justify suckers the high expense, EMI experts count power ratios
>> in Nipper as we all know.
>
> Wow, did RCA sell off Nipper as well?
>
I only knew Nipper as La Voix De Son Maitre (His Master's Voice), EMI,
>> > On Tuesday, May 21, 2013 11:58:27 AM UTC-7, Mark wrote:
>> >> it's a team effort, you really have no choice now but to leave the
>> >> CM
>> >>
>> >> chokes in because..
>> >>
>> >>
>> >>
>> >> if you convince the EMI guru to take them out now ,,,, and in the
>> >>
>> >> future, there is ANY kind of an EMI issue, it will be YOUR fault.
>> >>
>> >>
>> >>
>> >> If they don't hurt anything, leave them in and move on.
>> >>
>> >>
>> >>
>> >> Mark
>> >
>> > Mark, you make a good point but this guru will rain on my parade
>> > forever and that s$it must stop. He also gets paid a lot more than
>> > me and that PMO!!
>>
>> Hey, EMI wasn't Master's Voice for no reason.
>> And to justify suckers the high expense, EMI experts count power ratios
>> in Nipper as we all know.
>
> Wow, did RCA sell off Nipper as well?
>
JVC and Deutsche Grammophon, which already is an all mess.
The actual situation seems to be even worse...
All (ahem) the story is here
http://en.wikipedia.org/wiki/Nipper
and there
http://en.wikipedia.org/wiki/His_Master%27s_Voice
--
Thanks,
Fred.
Joerg
May 22, 2013, 12:56:58 PM5/22/13
to
Swap the opamp against a CMOS type if one is available that has
otherwise acceptable specs. Those do not have BE junctions behind the
input pins that could rectify.
In one case (across the Bay from you guys) that measure alone killed the
noise dead, as John Wayne would have put it. It was GSM cell phones
getting in there, something where regular beads aren't very effective
anymore unless you use the special Murata thingamagics, and those need
super-direct ground contact plus shield in order to work.
George Herold
May 22, 2013, 12:59:36 PM5/22/13
to
On May 22, 12:02 pm, John Larkin
> https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/Bead_L9...
Say if you passed one of the TC leads through it in the other
direction would that make it a one turn CM choke? (Just trying to
expand my transformer understanding.)
George H.
>
> --
>
> John Larkin Highland Technology Incwww.highlandtechnology.com jlarkin at highlandtechnology dot com
>
> - Show quoted text -
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Wed, 22 May 2013 07:56:46 -0700 (PDT), Harry D <har...@tdsystems.org> wrote:
> >On Tuesday, May 21, 2013 2:25:31 PM UTC-7, John Larkin wrote:
> >> On Tue, 21 May 2013 17:14:02 -0400, Spehro Pefhany
>
> On Wed, 22 May 2013 07:56:46 -0700 (PDT), Harry D <har...@tdsystems.org> wrote:
> >On Tuesday, May 21, 2013 2:25:31 PM UTC-7, John Larkin wrote:
> >> On Tue, 21 May 2013 17:14:02 -0400, Spehro Pefhany
>
>
> and it helped by something like 30 dB, and especially broke up narrowband
> resonances.
>
> I got this business by doing this better than their previous vendor. An RF
> generator could shut down his controller from clear across the room. I've sold
> over 3000 controllers so far, not bad for a "stinkin bead."
"Good bead" :^)
> and it helped by something like 30 dB, and especially broke up narrowband
> resonances.
>
> I got this business by doing this better than their previous vendor. An RF
> generator could shut down his controller from clear across the room. I've sold
> over 3000 controllers so far, not bad for a "stinkin bead."
Say if you passed one of the TC leads through it in the other
direction would that make it a one turn CM choke? (Just trying to
expand my transformer understanding.)
George H.
>
> --
>
> John Larkin Highland Technology Incwww.highlandtechnology.com jlarkin at highlandtechnology dot com
>
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom timing and laser controllers
> Photonics and fiberoptic TTL data links
> VME analog, thermocouple, LVDT, synchro, tachometer
> Multichannel arbitrary waveform generators- Hide quoted text -
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom timing and laser controllers
> Photonics and fiberoptic TTL data links
> VME analog, thermocouple, LVDT, synchro, tachometer
>
> - Show quoted text -
John Walliker
May 22, 2013, 1:06:42 PM5/22/13
to
On May 22, 5:56 pm, Joerg <inva...@invalid.invalid> wrote:
> In such unwanted rectification scenarios there is also another option:
> Swap the opamp against a CMOS type if one is available that has
> otherwise acceptable specs. Those do not have BE junctions behind the
> input pins that could rectify.
>
Yes, very effective indeed.
> In such unwanted rectification scenarios there is also another option:
> Swap the opamp against a CMOS type if one is available that has
> otherwise acceptable specs. Those do not have BE junctions behind the
> input pins that could rectify.
>
John
Spehro Pefhany
May 22, 2013, 1:18:38 PM5/22/13
to
Harry D
May 22, 2013, 1:22:56 PM5/22/13
to
Phil Hobbs
May 22, 2013, 1:27:01 PM5/22/13
to
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
Phil Hobbs
May 22, 2013, 1:34:42 PM5/22/13
to
On 05/22/2013 01:22 PM, Harry D wrote:
> On Wednesday, May 22, 2013 9:02:56 AM UTC-7, John Larkin wrote:
>> On Wed, 22 May 2013 07:56:46 -0700 (PDT), Harry D
>> <har...@tdsystems.org> wrote:
>>
>>
>>
>>> On Tuesday, May 21, 2013 2:25:31 PM UTC-7, John Larkin wrote:
>>
<snip>
> On Wednesday, May 22, 2013 9:02:56 AM UTC-7, John Larkin wrote:
>> On Wed, 22 May 2013 07:56:46 -0700 (PDT), Harry D
>> <har...@tdsystems.org> wrote:
>>
>>
>>
>>> On Tuesday, May 21, 2013 2:25:31 PM UTC-7, John Larkin wrote:
>>
>>
>> This is a thermocouple input, and it's heavily lowpass filtered by
>> RCs, and then by software filtering. The tc cable is a shielded
>> pair. Unfortunately, the tc is inside an NMR probe, along with high
>> field levels of RF in the 50-500 MHz range.
>>
>> The RF did (always will) get into the signal conditioning opamps
>> and get rectified to small offsets, in a system where 1 microvolt
>> matters. I added this bead
>>
>> https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/Bead_L900.JPG
>>
>> and it helped by something like 30 dB, and especially broke up
>> narrowband resonances.
>>
>> I got this business by doing this better than their previous
>> vendor. An RF generator could shut down his controller from clear
>> across the room. I've sold over 3000 controllers so far, not bad
>> for a "stinkin bead."
>> This is a thermocouple input, and it's heavily lowpass filtered by
>> RCs, and then by software filtering. The tc cable is a shielded
>> pair. Unfortunately, the tc is inside an NMR probe, along with high
>> field levels of RF in the 50-500 MHz range.
>>
>> The RF did (always will) get into the signal conditioning opamps
>> and get rectified to small offsets, in a system where 1 microvolt
>> matters. I added this bead
>>
>> https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/Bead_L900.JPG
>>
>> and it helped by something like 30 dB, and especially broke up
>> narrowband resonances.
>>
>> I got this business by doing this better than their previous
>> vendor. An RF generator could shut down his controller from clear
>> across the room. I've sold over 3000 controllers so far, not bad
>> for a "stinkin bead."
> John, your TC signal came into a diff-amp that rectifies at >1.0MHz.
> My single ended signal, after filtering, comes into a ADC with a
> bandwidth <1.0MHz. That stinken bead is worthless at <1.0MHz.
>
If you put your GSM phone on top of your stereo, you'll intermittently
> My single ended signal, after filtering, comes into a ADC with a
> bandwidth <1.0MHz. That stinken bead is worthless at <1.0MHz.
>
hear the 217 Hz pulse rep rate. That's all happening up in the
gigahertz, and there sure isn't anything in that stereo that's that
fast. It's rectification and other nonlinearity you have to worry
about.
I'm sympathetic to your dislike of having your designs messed with, but
if you don't know the origin of the EMI sensitivity, how are you able to
assess the other guy's work?
John Larkin
May 22, 2013, 2:36:28 PM5/22/13
to
On Wed, 22 May 2013 09:56:58 -0700, Joerg <inv...@invalid.invalid>
wrote:
Jfets are pretty good, too. Somebody, National maybe?, did a paper on
opamp RF sensitivity. And somebody makes an IA that has explicit RF
rectification protection.
Some opamps make damned fine RF detectors.
>
>In one case (across the Bay from you guys) that measure alone killed the
>noise dead, as John Wayne would have put it. It was GSM cell phones
>getting in there, something where regular beads aren't very effective
>anymore unless you use the special Murata thingamagics, and those need
>super-direct ground contact plus shield in order to work.
We have another recent bead application. We make a pair of VME and VXI
crate controllers, and we have to drive a shipload of address and data
lines, and VME is a messy bus, impedance-wise. We were seeing some
serious undershoots along the bus, -1.5 or so, because modern bus
drivers are screaming fast. And we had crosstalk concerns. We are
spinning the board layouts anyhow, so we put a mess of tiny quad beads
on the board, in series with all the VMEbus lines. So now we have a
nice 3 ns falling edge and about half a volt of max undershoot, a
downright purty waveform.
wrote:
opamp RF sensitivity. And somebody makes an IA that has explicit RF
rectification protection.
Some opamps make damned fine RF detectors.
>
>In one case (across the Bay from you guys) that measure alone killed the
>noise dead, as John Wayne would have put it. It was GSM cell phones
>getting in there, something where regular beads aren't very effective
>anymore unless you use the special Murata thingamagics, and those need
>super-direct ground contact plus shield in order to work.
crate controllers, and we have to drive a shipload of address and data
lines, and VME is a messy bus, impedance-wise. We were seeing some
serious undershoots along the bus, -1.5 or so, because modern bus
drivers are screaming fast. And we had crosstalk concerns. We are
spinning the board layouts anyhow, so we put a mess of tiny quad beads
on the board, in series with all the VMEbus lines. So now we have a
nice 3 ns falling edge and about half a volt of max undershoot, a
downright purty waveform.
whit3rd
May 22, 2013, 2:55:28 PM5/22/13
to
On Tuesday, May 21, 2013 11:58:27 AM UTC-7, Mark wrote:
> it's a team effort, you really have no choice now but to leave the CM
> chokes in because..
> if you convince the EMI guru to take them out now ,,,, and in the
> future, there is ANY kind of an EMI issue, it will be YOUR fault.
Yeah, if you're wrong when you say to take them out. It's never
> chokes in because..
> if you convince the EMI guru to take them out now ,,,, and in the
> future, there is ANY kind of an EMI issue, it will be YOUR fault.
going to be a 'no choice now' situation, though: stand and fight.
The defensive "do EVERYTHING we can" style is bad engineering,
bad tactics. Your job is to use planning time and resources to
good effect, and project hardware bloat is NOT a good effect.
> If they don't hurt anything, leave them in and move on.
Mark
May 22, 2013, 10:35:33 PM5/22/13
to
we are talking about a few pennies worth of parts, i'm not sure I
would use the word evil.
if the EMI guy is responsible for the EMI compatibility issues and he
wants the CM filters in, I would let it go. It's his contribution to
the effort, do not minimize it.
You never know, there may be 5 GHz RF fields and the CM filters help.
You never know, some issue, EMI or otherwise, may come up in the
future and having those CM filter pads on the PWB may be helpful.
It's cheap insurance.
Most importantly, maintaining a good working relationship with other
members of the team is worth ,much more then the few cents for the
parts. If the customer insists on the EMI guy being part of the
team, I would even suggest soliciting the EMI guys input at the start
of the next project.
The real issues here are much larger then engineering.
Mark
John Larkin
May 23, 2013, 12:09:57 AM5/23/13
to
--
John Larkin Highland Technology Inc
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
Jasen Betts
May 23, 2013, 4:04:06 AM5/23/13
to
On 2013-05-21, Joerg <inv...@invalid.invalid> wrote:
--
⚂⚃ 100% natural
--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---
> Jim Thompson wrote:
>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>> <har...@tdsystems.org> wrote:
>>
>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>> What is my best arugment to have them replaced with a short?
>>>
>>> Harry
>>
>
>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>> <har...@tdsystems.org> wrote:
>>
>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>> What is my best arugment to have them replaced with a short?
>>>
>>> Harry
>>
>
> Hmm, for some reason I can't see the original post.
Have you killfiled google?
--
⚂⚃ 100% natural
--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---
Joerg
May 23, 2013, 9:57:48 AM5/23/13
to
Jasen Betts wrote:
> On 2013-05-21, Joerg <inv...@invalid.invalid> wrote:
>> Jim Thompson wrote:
>>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>>> <har...@tdsystems.org> wrote:
>>>
>>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>>> What is my best arugment to have them replaced with a short?
>>>>
>>>> Harry
>> Hmm, for some reason I can't see the original post.
>
> Have you killfiled google?
>
I used to, until my news provider (www.individual.de) began to do a
> On 2013-05-21, Joerg <inv...@invalid.invalid> wrote:
>> Jim Thompson wrote:
>>> On Tue, 21 May 2013 08:45:08 -0700 (PDT), Harry D
>>> <har...@tdsystems.org> wrote:
>>>
>>>> I'm working with a group designing avionics equipment and they recently hired an EMI guru. He insists on placing CM chokes on every single ended I/O signal line. These signals can be floating 100K thermistors that are received by a Pi filter (100K resistor and two 1.0uF caps to ground). The miniture CM chokes are 1k at 100MHz (1.6uH).
>>>> What is my best arugment to have them replaced with a short?
>>>>
>>>> Harry
>> Hmm, for some reason I can't see the original post.
>
> Have you killfiled google?
>
really good job of hosing off spam. The ads for the fake Gucci handbags
and all that. But it let posts from David Jones (who unfortunately uses
googlemail) through without a problem, something my own filter wasn't
able to do. Then I took my filter out, there is no killfile in my
newsreader.
The news provider occasionally filter out some other legit posts, but
mostly only Jim's, for whatever reason. Maybe they use a routine that a
certain agency lately ... well, let's not go there :-)
Spehro Pefhany
May 23, 2013, 11:19:47 AM5/23/13
to
On Wed, 22 May 2013 21:09:57 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Wed, 22 May 2013 11:55:28 -0700 (PDT), whit3rd <whi...@gmail.com> wrote:
>
>>On Tuesday, May 21, 2013 11:58:27 AM UTC-7, Mark wrote:
>>> it's a team effort, you really have no choice now but to leave the CM
>>> chokes in because..
>>
>>> if you convince the EMI guru to take them out now ,,,, and in the
>>> future, there is ANY kind of an EMI issue, it will be YOUR fault.
>>
>>Yeah, if you're wrong when you say to take them out. It's never
>>going to be a 'no choice now' situation, though: stand and fight.
>>The defensive "do EVERYTHING we can" style is bad engineering,
>>bad tactics. Your job is to use planning time and resources to
>>good effect, and project hardware bloat is NOT a good effect.
>>
>>> If they don't hurt anything, leave them in and move on.
>>
>>"No evil, no matter how small, ought to be tolerated." -- Aesop
>
>Clearly Aesop wasn't an engineer.
If the level of evil is guaranteed to be substantially less than the
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Wed, 22 May 2013 11:55:28 -0700 (PDT), whit3rd <whi...@gmail.com> wrote:
>
>>On Tuesday, May 21, 2013 11:58:27 AM UTC-7, Mark wrote:
>>> it's a team effort, you really have no choice now but to leave the CM
>>> chokes in because..
>>
>>> if you convince the EMI guru to take them out now ,,,, and in the
>>> future, there is ANY kind of an EMI issue, it will be YOUR fault.
>>
>>Yeah, if you're wrong when you say to take them out. It's never
>>going to be a 'no choice now' situation, though: stand and fight.
>>The defensive "do EVERYTHING we can" style is bad engineering,
>>bad tactics. Your job is to use planning time and resources to
>>good effect, and project hardware bloat is NOT a good effect.
>>
>>> If they don't hurt anything, leave them in and move on.
>>
>>"No evil, no matter how small, ought to be tolerated." -- Aesop
>
>Clearly Aesop wasn't an engineer.
specified limit, it's probably overdesigned.
josephkk
May 23, 2013, 10:36:47 PM5/23/13
to
On Tue, 21 May 2013 11:58:27 -0700 (PDT), Mark <mako...@yahoo.com> wrote:
>it's a team effort, you really have no choice now but to leave the CM
>chokes in because..
>
>if you convince the EMI guru to take them out now ,,,, and in the
>future, there is ANY kind of an EMI issue, it will be YOUR fault.
>
>it's a team effort, you really have no choice now but to leave the CM
>chokes in because..
>
>if you convince the EMI guru to take them out now ,,,, and in the
>future, there is ANY kind of an EMI issue, it will be YOUR fault.
>
>If they don't hurt anything, leave them in and move on.
>
>Mark
>
>
But they do hurt. They cost money. They do not provide the intended
value. And worst of all they teach erroneous design techniques to the
easily swayed. Costing lots of money permanently.
A far better design would use a tapped inductor 2 turns to the outside
world per turn to inside on the two sides of the tap; then place a cap to
ground at the tap. Toroids or closed pot cores preferred.
Measure the performance difference in front of management.
?-)
josephkk
May 23, 2013, 10:56:28 PM5/23/13
to
On Tue, 21 May 2013 12:25:36 -0700 (PDT), Harry D <har...@tdsystems.org>
wrote:
>
That is a very different case. The CM choke might actually help. Drawing
the circuit diagram.
___________@@@@___________> to measuring circuit
Therm O=======CMchoke===<_ | |
| _|_ _|_
| ___ ___
| | |
|_____|___________|
_|_
//// Pi filter
Do you see how it is not a transformer with a shorted secondary in this
case?
?-)
wrote:
>
> If the CM choke is not used then the other lead goes to ground and the signal is "single ended".
> But you knew that already.
> Cheers, Harry
> But you knew that already.
That is a very different case. The CM choke might actually help. Drawing
the circuit diagram.
___________@@@@___________> to measuring circuit
Therm O=======CMchoke===<_ | |
| _|_ _|_
| ___ ___
| | |
|_____|___________|
_|_
//// Pi filter
Do you see how it is not a transformer with a shorted secondary in this
case?
?-)
Joerg
May 24, 2013, 12:04:22 PM5/24/13
to
it's a cheese, right? Yes, it is a cheese!
http://www.thelaughingcow.com/about-us/
John Larkin
May 24, 2013, 12:50:22 PM5/24/13
to
Why not a 5-cent dual ferrite bead?
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
0 new messages