Today's Message Index:
----------------------
1. 05:21 AM - Re: Re: Thermocouple leads (Steve Stearns)
2. 07:31 AM - alternator wiring (Kenneth Johnson)
3. 07:43 AM - Re: Re: Thermocouple leads (Robert L. Nuckolls, III)
4. 08:11 AM - Re: Re: Thermocouple leads (Robert L. Nuckolls, III)
5. 08:13 AM - Re: Re: Thermocouple leads (Robert L. Nuckolls, III)
6. 10:19 AM - Re: alternator wiring (Robert L. Nuckolls, III)
7. 12:21 PM - Re: Re: Thermocouple leads (David)
8. 01:37 PM - Shrink tubing shrinker. (rayj)
9. 04:54 PM - Re: Re: Thermocouple leads (Robert L. Nuckolls, III)
10. 05:02 PM - Re: Shrink tubing shrinker. (Robert L. Nuckolls, III)
11. 07:36 PM - Com and Nav Radio and Antenna Questions (Don)
Message 1
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Subject: | Re: Thermocouple leads |
Group,
Although it's made clear enough in the book, I don't think it's come
through clear enough yet in this thread that when using dissimilar
junctions you ALSO have to worry that you don't inadvertently move the
reference (i.e. "cold") junction(s).
As an illustration, my Long-EZ, when received, had a short pigtail on
the under-sparkplug CHT T-couple. It was transitioned to copper pretty
much adjacent to the neighboring cylinder. The copper ran all the way
to a powered (i.e. high impedance) Westach gauge. The Westach is
designed (best I can tell) so that the cold junction(s) (i.e. the final
terminations to non-T-couple wire) are actually made by the junctions
that result from the crimps between what is supposed to be T-couple wire
and fast-on connectors right at the back of the gauge. This allows a
temp sensor in the gauge to compensate for the voltages at the cold
junctions.
By running copper from the T-couple wire pig-tails all the way to the
gauge, there would usually be a significant temperature difference
between the actual cold junctions (next to a cylinder) and the intended
cold junctions (behind the panel) which would show up directly in error
on the reading of the gauge. That's all fixed now...
Steve Stearns
Boulder/Longmont, Colorado
CSA,EAA,IAC,AOPA,PE,ARRL,BARC (but ignorant none-the-less)
Restoring (since 1/07) and flying again (8/11!): N45FC O235 Longeze
Cothern/Friling CF1 (~1000 Hrs)
Flying (since 9/86): N43732 A65 Taylorcraft BC12D
Message 2
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Subject: | alternator wiring |
Bob and All,=0AI have appreciated all the information received during the l
ast year or two as I have been preparing to wire my panel.- The time has
come.- I have a question regarding the wiring of my alternator, a Bosch A
L394X.- I have tried to find wiring schemes on the internet, but have not
been able to download what I need.- I have included a picture to help.
-- At about 12 o'clock, I assume the large, black connecter goes to the
battery.- What should be done with the connector plug at about 10 o'cloc
k above the center hub and the two connector plug at about 6 o'clock below
the center hub?- Thanks for your help!!!- Ken Johnson=0A
Message 3
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Subject: | Re: Thermocouple leads |
At 07:15 AM 2/4/2012, you wrote:
Group,
Although it's made clear enough in the book, I don't think it's come
through clear enough yet in this thread that when using dissimilar
junctions you ALSO have to worry that you don't inadvertently move
the reference (i.e. "cold") junction(s).
As an illustration, my Long-EZ, when received, had a short pigtail on
the under-sparkplug CHT T-couple. It was transitioned to copper
pretty much adjacent to the neighboring cylinder. The copper ran all
the way to a powered (i.e. high impedance) Westach gauge. The
Westach is designed (best I can tell) so that the cold junction(s)
(i.e. the final terminations to non-T-couple wire) are actually made
by the junctions that result from the crimps between what is supposed
to be T-couple wire and fast-on connectors right at the back of the
gauge. This allows a temp sensor in the gauge to compensate for the
voltages at the cold junctions.
By running copper from the T-couple wire pig-tails all the way to the
gauge, there would usually be a significant temperature difference
between the actual cold junctions (next to a cylinder) and the
intended cold junctions (behind the panel) which would show up
directly in error on the reading of the gauge. That's all fixed now...
Exactly. I've often thought that we should perhaps
forsake the term "cold junction" for "reference junction".
Classically, the reference junction was any point in the
system where the transition from thermocouple alloys
and instrumentation was known with accuracy. It could
be hotter or colder than the temperature of interest.
I recall the first thermocouple array I ever saw installed on
a flight test airplane at Cessna. The reference junction
for perhaps a dozen switched thermocouples was submerged
in a Thermos bottle filled with crushed ice made with
distilled water. Pretty durn close to 0 degrees C.
But the self powered instruments couldn't be fitted with
ice baths so an alternative reference junction compensation
scheme had to be crafted. I've been meaning to dig through
the old patents someday and see what the popular techniques
were 70 years ago. In that test setup, a flight test technician
had to measure each thermocouple one at a time using a precision
potentiometer bridge in his lap. The millivolt readings were
written to a test data sheet and converted to temperatures
later when he wrote his test report.
Tedious . . .
Emacs!
A modern incarnation for implementing a reference junction
is illustrated here:
Emacs!
I think this is out of an analog devices AppNote illustrating how
an AD592 temperature sensor is situated in thermal proximity to a
T/C-to-Copper
reference junction. Thus, while the "reference" can be wandering around
with ambient temperature, it's effect on output is known and
compensated for. Even this technique is outdated since Analog Devices
and others have created thermocouple conditioner chips that feature
built in reference junction sensing features and offer user friendly
10 mv/degree output signals.
The situation in your airplane as-received could be illustrated
like this:
Emacs!
The indiscriminate insertion of a "rogue" junction added new but
unknown effects that the instrument would not be able to resolve
resulting in wildly inaccurate readings.
Bob . . .
Message 4
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Subject: | Re: Thermocouple leads |
At 03:53 AM 2/2/2012, you wrote:
Another "lightbulb" reply, thank you. I know I've
read this in the Connection, but still, a reminder doesn't go amiss.
Is this effect mitigated by having a common
ground on the firewall, with a braided strap to
the engine? If the instruments are grounded to
the forest of tabs, and that's only a short
distance along a fat piece of copper to the engine...
Yes. If you're using a forest of tabs firewall
ground and have the fat braid to the crankcase,
I'd be surprised if you have a ground loop issue
with the thermocouples.
At 01:20 PM 2/1/2012, you wrote:
I'll second that. On the Dynon an improper ground
on 1 device/sensor can/will impact the reading on
another. I used to have an old Cadillac which
when you moved the electric seat the high beams
flashed. They called it a feature.
Hmmmm . . . how do you mean "improper ground" on a
sensor? Are we talking thermocouples here? In the
case of a thermocouple welded down to it's thermowell,
the installer has no control over the existence or
quality of that ground.
When considering devices like temperature or pressure
sensors, if they're fitted with ground wires, then
that wire should be brought back to the point where
the instrument grounds . . . either the forest of
tabs on the firewall or the instrument panel ground.
If the sensor gets grounded by virtue of it's being
attached to the engine (common with automotive devices)
then again, the installer has little control over
any voltage differentials that the the sensor ground
verus the instrument ground . . . except to bring
the two a close together as possible (forest of tabs)
and use a fat bonding jumper.
If improper delivery of signal to one channel of
the instrument can upset readings of other channels,
then the instrument at least suspected of poor
design. I'd find that hard to believe of Dynon.
Bob . . .
Message 5
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Subject: | Re: Thermocouple leads |
The second image got hosed during a cut-n-paste. Here's
how the message SHOULD have looked. -BN-
-
At 07:15 AM 2/4/2012, you wrote:
Group,
Although it's made clear enough in the book, I don't think it's come
through clear enough yet in this thread that when using dissimilar
junctions you ALSO have to worry that you don't inadvertently move
the reference (i.e. "cold") junction(s).
As an illustration, my Long-EZ, when received, had a short pigtail on
the under-sparkplug CHT T-couple. It was transitioned to copper
pretty much adjacent to the neighboring cylinder. The copper ran all
the way to a powered (i.e. high impedance) Westach gauge. The
Westach is designed (best I can tell) so that the cold junction(s)
(i.e. the final terminations to non-T-couple wire) are actually made
by the junctions that result from the crimps between what is supposed
to be T-couple wire and fast-on connectors right at the back of the
gauge. This allows a temp sensor in the gauge to compensate for the
voltages at the cold junctions.
By running copper from the T-couple wire pig-tails all the way to the
gauge, there would usually be a significant temperature difference
between the actual cold junctions (next to a cylinder) and the
intended cold junctions (behind the panel) which would show up
directly in error on the reading of the gauge. That's all fixed now...
Exactly. I've often thought that we should perhaps
forsake the term "cold junction" for "reference junction".
Classically, the reference junction was any point in the
system where the transition from thermocouple alloys
and instrumentation was known with accuracy. It could
be hotter or colder than the temperature of interest.
I recall the first thermocouple array I ever saw installed on
a flight test airplane at Cessna. The reference junction
for perhaps a dozen switched thermocouples was submerged
in a Thermos bottle filled with crushed ice made with
distilled water. Pretty durn close to 0 degrees C.
But the self powered instruments couldn't be fitted with
ice baths so an alternative reference junction compensation
scheme had to be crafted. I've been meaning to dig through
the old patents someday and see what the popular techniques
were 70 years ago. In that test setup, a flight test technician
had to measure each thermocouple one at a time using a precision
potentiometer bridge in his lap. The millivolt readings were
written to a test data sheet and converted to temperatures
later when he wrote his test report.
Tedious . . .
Emacs!
A modern incarnation for implementing a reference junction
is illustrated here:
Emacs!
I think this is out of an analog devices AppNote illustrating how
an AD592 temperature sensor is situated in thermal proximity to a
T/C-to-Copper
reference junction. Thus, while the "reference" can be wandering around
with ambient temperature, it's effect on output is known and
compensated for. Even this technique is outdated since Analog Devices
and others have created thermocouple conditioner chips that feature
built in reference junction sensing features and offer user friendly
10 mv/degree output signals.
The situation in your airplane as-received could be illustrated
like this:
Emacs!
The indiscriminate insertion of a "rogue" junction added new but
unknown effects that the instrument would not be able to resolve
resulting in wildly inaccurate readings.
Bob . . .
Message 6
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Subject: | Re: alternator wiring |
At 09:23 AM 2/4/2012, you wrote:
Bob and All,
I have appreciated all the information received during the last year
or two as I have been preparing to wire my panel. The time has
come. I have a question regarding the wiring of my alternator, a
Bosch AL394X. I have tried to find wiring schemes on the internet,
but have not been able to download what I need. I have included a
picture to help. At about 12 o'clock, I assume the large, black
connecter goes to the battery.
Yes
What should be done with the connector plug at about 10 o'clock
above the center hub . . .
Leave it open
and the two connector plug at about 6 o'clock below the center
hub? Thanks for your help!!! Ken Johnson
Ignore the "lamp" connection. Connect your control
input wire to "IGN". Do you have a plan for dealing with
an OV condition?
Emacs!
Bob . . .
Message 7
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Subject: | Re: Thermocouple leads |
Bob, I'm using the AD594/595 and it is my understanding that even with
all the magic inside the chip, one has to compensate for the extra cold
junctions aka reference junctions.
David
Robert L. Nuckolls, III wrote:
> At 07:15 AM 2/4/2012, you wrote:
> <steve@tomasara.com>
>
> Group,
>
> Although it's made clear enough in the book, I don't think it's come
> through clear enough yet in this thread that when using dissimilar
> junctions you ALSO have to worry that you don't inadvertently move the
> reference (i.e. "cold") junction(s).
>
> As an illustration, my Long-EZ, when received, had a short pigtail on
> the under-sparkplug CHT T-couple. It was transitioned to copper
> pretty much adjacent to the neighboring cylinder. The copper ran all
> the way to a powered (i.e. high impedance) Westach gauge. The Westach
> is designed (best I can tell) so that the cold junction(s) (i.e. the
> final terminations to non-T-couple wire) are actually made by the
> junctions that result from the crimps between what is supposed to be
> T-couple wire and fast-on connectors right at the back of the gauge.
> This allows a temp sensor in the gauge to compensate for the voltages
> at the cold junctions.
>
> By running copper from the T-couple wire pig-tails all the way to the
> gauge, there would usually be a significant temperature difference
> between the actual cold junctions (next to a cylinder) and the
> intended cold junctions (behind the panel) which would show up
> directly in error on the reading of the gauge. That's all fixed now...
>
> Exactly. I've often thought that we should perhaps
> forsake the term "cold junction" for "reference junction".
> Classically, the reference junction was any point in the
> system where the transition from thermocouple alloys
> and instrumentation was known with accuracy. It could
> be hotter or colder than the temperature of interest.
> I recall the first thermocouple array I ever saw installed on
> a flight test airplane at Cessna. The reference junction
> for perhaps a dozen switched thermocouples was submerged
> in a Thermos bottle filled with crushed ice made with
> distilled water. Pretty durn close to 0 degrees C.
>
> But the self powered instruments couldn't be fitted with
> ice baths so an alternative reference junction compensation
> scheme had to be crafted. I've been meaning to dig through
> the old patents someday and see what the popular techniques
> were 70 years ago. In that test setup, a flight test technician
> had to measure each thermocouple one at a time using a precision
> potentiometer bridge in his lap. The millivolt readings were
> written to a test data sheet and converted to temperatures
> later when he wrote his test report.
>
> Tedious . . .
>
> Emacs!
>
> A modern incarnation for implementing a reference junction
> is illustrated here:
>
> Emacs!
>
> I think this is out of an analog devices AppNote illustrating how
> an AD592 temperature sensor is situated in thermal proximity to a
> T/C-to-Copper
> reference junction. Thus, while the "reference" can be wandering around
> with ambient temperature, it's effect on output is known and
> compensated for. Even this technique is outdated since Analog Devices
> and others have created thermocouple conditioner chips that feature
> built in reference junction sensing features and offer user friendly
> 10 mv/degree output signals.
>
> The situation in your airplane as-received could be illustrated
> like this:
>
> Emacs!
>
> The indiscriminate insertion of a "rogue" junction added new but
> unknown effects that the instrument would not be able to resolve
> resulting in wildly inaccurate readings.
>
> Bob . . .
>
--
Tell the truth. Be honest. Be responsible to and for yourself.
We want our freedoms back. Strike the illegal legislations called: 1) obamacare,
2) "Patriot (HA!) Act", and 3) 'presidential orders' that affect anyone besides
gubmnt worker bees.
Hate crime laws? Really? Thought police? Orwell would be proud.
Every gram of cocaine you buy from elsewhere contributes to an innocent being murdered
in Central and South America. Grow your own or Stop taking it.
Message 8
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Subject: | Shrink tubing shrinker. |
Greetings listers,
I have been using a heat gun type thing that I got at a g-sale and the
results are consistently satisfactory so I thought I'd share the info
with the list. The tool is called an "embossing heat tool". They are
sold at fabric craft stores and are used to heat embossing ink that is
applied to fabric and then heated to create embossed patterns. The one
I have is 360 watts. It's hot enough to melt the glue inside and shrink
the tubing but you would have to work really hard to melt even PVC
insulation. I find I can apply the heat for as long as I need to get
the max shrink without really worrying about burning it.
--
Raymond Julian
Kettle River, MN
"And you know that I could have me a million more friends,
and all I'd have to lose is my point of view." - John Prine
Message 9
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Subject: | Re: Thermocouple leads |
At 01:48 PM 2/4/2012, you wrote:
>
>Bob, I'm using the AD594/595 and it is my understanding that even
>with all the magic inside the chip, one has to compensate for the
>extra cold junctions aka reference junctions.
No. See
http://tinyurl.com/6xp4xc
In the features list right on the front cover we see
the statement "Built-In Ice Point Compensation".
In Figure 13 we see an interesting use of the 594/595
as a Celsius thermometer. Just short the t/c pins together
and the chip reports it's own internal temperature (very
close to ambient).
In the data acquisition signal conditioner I illustrated
at:
http://aeroelectric.com/Pictures/Data_Acquisition/Weeder_Module_DAS_4.jpg
. . . one of those thermocouple conditioner chips was used
for just that purpose. This gizmo was installed in the nose
of a Beechjet for some pitot temperature studies at high
altitude. Some of the integrated circuits were qualified
down only to 0 degrees C. If you look at the picture
you can see a power resistor peeking out from under the
perf-board. That resistor and three others were used as
heaters controlled by one of the T/C chips to maintain
10C inside the box.
So, I'm happy to report that these critters are very complete
and require no ice-point reference junctions.
Bob . . .
Message 10
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Subject: | Re: Shrink tubing shrinker. |
At 03:33 PM 2/4/2012, you wrote:
>
>Greetings listers,
>
>I have been using a heat gun type thing that I got at a g-sale and
>the results are consistently satisfactory so I thought I'd share the
>info with the list. The tool is called an "embossing heat tool".
Cool find sir! I'll pick one up when I'm in Wichita
this weekend and see what they're like. Years ago
I was pretty attached to my Weller "Princess" model
heat guns. They were something on the order of 250W
and delivered heat out a very compact nozzle. Nice
for close quarters work. They were not very robust
and the two I had eventually died but I was loath to
spend the $100+ to replace them.
These look like they might be an attractive, low cost
alternative. Thanks for the heads-up.
Bob . . .
Message 11
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Subject: | Com and Nav Radio and Antenna Questions |
Bob and Listers
When taking a standing wave ratio reading is it necessary to key the
transmit button?
If the above is correct how does one match nav radios to coax and antennas?
I am trying to help a friend with a Pitts that has radio problems. He flew
today and could not hear the attis at KWHP on the ground or in the air. The
attis was functioning . Frequency 132,1
On the downwind departure leg he lost contact with the tower at less than a
mile from the airport frequency 135.0
He also lost ground at the same time frequency 125.0
He was able to hear KBUR attis and tower frequencies 135.125 and 134-5
tower 118.7 even though Burbank is in a straight line with Whitman and
further away.
He was able to hear KVNY attis and tower frequencies 118.45 tower 1193 and
continued to hear them for at least 10 miles further away. Burkank also
continued to be heard. Radio is an Icom and there have been two antennas
tried a Rami bent whip mounted on the only piece of flat plate in the
aircraft and an archer mounted inside the wooden turtle deck. It was
suggested that the arched was having problems because of the anti UV coating
on the fabric so the Rami was installed and does not seem to work any
better.
Any ideas on where to start would be appreciated
Don
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