Colpitts Coil
 

You call that a coil? That's not a coil.
*This* is a coil!

Ed

Colpitts Coil
 

ehsjr wrote:
You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?

--
Regards, Joerg

http://www.analogconsultants.com/

Colpitts Coil
 

On Wed, 09 Jan 2008 11:11:58 -0800, Joerg
wrote:

ehsjr wrote:
You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?

Demonstrating the poor coupling of air-core inductors ?:-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

America: Land of the Free, Because of the Brave

Colpitts Coil
 

"Joerg" wrote in message
...
ehsjr wrote:
You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

I thought that was a canabis behind the bench

Colpitts Coil
 

Joerg wrote:
ehsjr wrote:

You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?


For a permeability tuned oscillator. It's an experiment to
measure water level, which changes only 3 feet nominal at
the site.

The finished coil is 42" of wire on 46" of PVC. A float
makes the coil ride up and down on a galvanized rod as
the water level changes.

It is accurate to within an inch, with +/- 3" being acceptable,
so that part is good. There is a big (ie 3" change in reading
with a 30F change in ambient) temperature problem to be solved,
but I ran out of warm weather to work on it. Looking for +/- 3"
accuracy between 50 and 100 F.

Ed

Colpitts Coil
 

"ehsjr" wrote in message
news:3qihj.3848$K%6.3695@trndny04...
Joerg wrote:
ehsjr wrote:

You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?


For a permeability tuned oscillator. It's an experiment to
measure water level, which changes only 3 feet nominal at
the site.

The finished coil is 42" of wire on 46" of PVC. A float
makes the coil ride up and down on a galvanized rod as
the water level changes.

It is accurate to within an inch, with +/- 3" being acceptable,
so that part is good. There is a big (ie 3" change in reading
with a 30F change in ambient) temperature problem to be solved,
but I ran out of warm weather to work on it. Looking for +/- 3"
accuracy between 50 and 100 F.

Ed

Where do you think the temperature effect is coming in - the oscillator
portion or the coil?
Some freeze spray is usually a good way to find gross effects of
temperature.

Does the inductance change also with temperature? An inductance bridge would
be helpful here.

How about using a LVDT approach instead?

Colpitts Coil
 

Oppie wrote:
"ehsjr" wrote in message
news:3qihj.3848$K%6.3695@trndny04...

Joerg wrote:

ehsjr wrote:


You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?


For a permeability tuned oscillator. It's an experiment to
measure water level, which changes only 3 feet nominal at
the site.

The finished coil is 42" of wire on 46" of PVC. A float
makes the coil ride up and down on a galvanized rod as
the water level changes.

It is accurate to within an inch, with +/- 3" being acceptable,
so that part is good. There is a big (ie 3" change in reading
with a 30F change in ambient) temperature problem to be solved,
but I ran out of warm weather to work on it. Looking for +/- 3"
accuracy between 50 and 100 F.

Ed


Where do you think the temperature effect is coming in - the oscillator
portion or the coil?
Some freeze spray is usually a good way to find gross effects of
temperature.

Does the inductance change also with temperature? An inductance bridge would
be helpful here.

How about using a LVDT approach instead?




Your question is right on target - it is "where I'm at"
in the experiment. Really, "where I got to" - but now
I have to wait for May with day and night temp over 50.

I think at least some of the temperature effect is coming
from the oscillator, in spite of the fact that it is
temperature compensated. (The output variation with
temperature is "solvable" at this point with a lookup table
and temperature input, but that is really addressing the
symptom, not the cause and adds complexity. Aside from that,
I'm more interested in pursuing it from the cause side of
things.)

The whole thing, at this stage, has to be outdoors - and that
includes the test equipment. The inductance measurement changes
with temperature, AIRC, but I don't know yet how much of that,
if any, is test equipment error. Using the frequency change
approach vs delta L makes a wider input, and small changes
in level were easier to see. I hadn't thought of pulsing a
current and measuring V.

I may have to jury rig something for testing to bring the
equipment inside where the temperature remains the same.

Ed

Colpitts Coil
 

"ehsjr" wrote in message
news:ALthj.4679$tZ6.1291@trndny03...
Oppie wrote:
"ehsjr" wrote in message
news:3qihj.3848$K%6.3695@trndny04...

Joerg wrote:

ehsjr wrote:


You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?


For a permeability tuned oscillator. It's an experiment to
measure water level, which changes only 3 feet nominal at
the site.

The finished coil is 42" of wire on 46" of PVC. A float
makes the coil ride up and down on a galvanized rod as
the water level changes.

It is accurate to within an inch, with +/- 3" being acceptable,
so that part is good. There is a big (ie 3" change in reading
with a 30F change in ambient) temperature problem to be solved,
but I ran out of warm weather to work on it. Looking for +/- 3"
accuracy between 50 and 100 F.

Ed


Where do you think the temperature effect is coming in - the oscillator
portion or the coil?
Some freeze spray is usually a good way to find gross effects of
temperature.

Does the inductance change also with temperature? An inductance bridge
would be helpful here.

How about using a LVDT approach instead?


Your question is right on target - it is "where I'm at"
in the experiment. Really, "where I got to" - but now
I have to wait for May with day and night temp over 50.

I think at least some of the temperature effect is coming
from the oscillator, in spite of the fact that it is
temperature compensated. (The output variation with
temperature is "solvable" at this point with a lookup table
and temperature input, but that is really addressing the
symptom, not the cause and adds complexity. Aside from that,
I'm more interested in pursuing it from the cause side of
things.)

The whole thing, at this stage, has to be outdoors - and that
includes the test equipment. The inductance measurement changes
with temperature, AIRC, but I don't know yet how much of that,
if any, is test equipment error. Using the frequency change
approach vs delta L makes a wider input, and small changes
in level were easier to see. I hadn't thought of pulsing a
current and measuring V.

I may have to jury rig something for testing to bring the
equipment inside where the temperature remains the same.

Ed

You've also got a lot of copper wire there in the coil that has a positive
tempco. Does a + tempco figure into your experimental results?

Does the frequency output stabilize immediately after power up or does it
drift to a 'stable' point? Perhaps pulsing the operation of the sensor is a
reasonable strategy.

What range of frequency are you expecting? You mentioned that the coil
assembly is attached to a float and rides over the fixed iron rod.
Hysteresis effects in the iron and capacitive effects between the coil and
surrounding water/air should be considered.

LVDTs are interesting since they ammount to a balanced bridge and the output
is the ratio of coupling between an excitation coil and two sensing coils.
Being balanced, common mode stuff falls out of the equation.

Colpitts Coil
 

On Thu, 10 Jan 2008 18:48:00 GMT, ehsjr
wrote:


The whole thing, at this stage, has to be outdoors - and that
includes the test equipment. The inductance measurement changes
with temperature, AIRC, but I don't know yet how much of that,
if any, is test equipment error. Using the frequency change
approach vs delta L makes a wider input, and small changes
in level were easier to see. I hadn't thought of pulsing a
current and measuring V.

I may have to jury rig something for testing to bring the
equipment inside where the temperature remains the same.

Ed

As a test, could you not bring everything into the kitchen? Measure
the inductance at room temperature, then put the coil in the fridge,
and watch for inductance changes as it cools.



--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Colpitts Coil
 

ehsjr wrote:
Joerg wrote:
ehsjr wrote:

You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?


For a permeability tuned oscillator. It's an experiment to
measure water level, which changes only 3 feet nominal at
the site.

The finished coil is 42" of wire on 46" of PVC. A float
makes the coil ride up and down on a galvanized rod as
the water level changes.

It is accurate to within an inch, with +/- 3" being acceptable,
so that part is good. There is a big (ie 3" change in reading
with a 30F change in ambient) temperature problem to be solved,
but I ran out of warm weather to work on it. Looking for +/- 3"
accuracy between 50 and 100 F.


Can't you run some additional DC through the coil and regulate that so
you get a constant DC resistance through the coil?

--
Regards, Joerg

http://www.analogconsultants.com/

Colpitts Coil
 

On Wed, 09 Jan 2008 11:11:58 -0800, Joerg wrote:
ehsjr wrote:
You call that a coil? That's not a coil.
*This* is a coil!

No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?

It looks kind of like a marigold, next to some pot. ;-)

Cheers!
Rich

Colpitts Coil
 

Peter Bennett wrote:
On Thu, 10 Jan 2008 18:48:00 GMT, ehsjr
wrote:



The whole thing, at this stage, has to be outdoors - and that
includes the test equipment. The inductance measurement changes
with temperature, AIRC, but I don't know yet how much of that,
if any, is test equipment error. Using the frequency change
approach vs delta L makes a wider input, and small changes
in level were easier to see. I hadn't thought of pulsing a
current and measuring V.

I may have to jury rig something for testing to bring the
equipment inside where the temperature remains the same.

Ed


As a test, could you not bring everything into the kitchen? Measure
the inductance at room temperature, then put the coil in the fridge,
and watch for inductance changes as it cools.




I don't think my wife would allow me the privilege
of living if I stuffed a 46" long PVC tube in
the fridge. :-)

Ed

Colpitts Coil
 

Joerg wrote:
ehsjr wrote:

Joerg wrote:

ehsjr wrote:

You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?


For a permeability tuned oscillator. It's an experiment to
measure water level, which changes only 3 feet nominal at
the site.

The finished coil is 42" of wire on 46" of PVC. A float
makes the coil ride up and down on a galvanized rod as
the water level changes.

It is accurate to within an inch, with +/- 3" being acceptable,
so that part is good. There is a big (ie 3" change in reading
with a 30F change in ambient) temperature problem to be solved,
but I ran out of warm weather to work on it. Looking for +/- 3"
accuracy between 50 and 100 F.


Can't you run some additional DC through the coil and regulate that so
you get a constant DC resistance through the coil?


Hadn't thought of that. As I recall, there's no DC in the
coil. My notes, circuit, schematic and coil are all buried
in the garage waiting for warm weather. But I'm fairly sure
it's a standard Colpitts with the coil connected to the base,
with no DC path.

I'm measuring frequency, which is what changes with temperature
change - I don't remember the direction. As I recall, it makes
an excellent thermometer, implying linear change. Anyway, my
assumption has been that either or both the capacitance and the
inductance are changing with delta T, and I expect the biggest
change is in C, not L. It seems highly probable that the caps
are the biggest source of the delta in Hz. Those assumptions are
what I need to examine next.

BTW - that's just one of the wacko coils I made. :-)
It started out only as a proof of concept thing, but
since I had already Rube Goldberged the "coil winder",
I did a few more of various configurations.

Ed

Colpitts Coil
 

ChairmanOfTheBored wrote:
On Thu, 10 Jan 2008 12:57:32 -0800, Peter Bennett
wrote:


On Thu, 10 Jan 2008 18:48:00 GMT, ehsjr
wrote:



The whole thing, at this stage, has to be outdoors - and that
includes the test equipment. The inductance measurement changes
with temperature, AIRC, but I don't know yet how much of that,
if any, is test equipment error. Using the frequency change
approach vs delta L makes a wider input, and small changes
in level were easier to see. I hadn't thought of pulsing a
current and measuring V.

I may have to jury rig something for testing to bring the
equipment inside where the temperature remains the same.

Ed

As a test, could you not bring everything into the kitchen? Measure
the inductance at room temperature, then put the coil in the fridge,
and watch for inductance changes as it cools.



How is he going to get three feet of water into his fridge? Also the
float rod?

:-)

Maybe I could move it to the twilight zone?

Ed

Colpitts Coil
 

ehsjr wrote:
Joerg wrote:
ehsjr wrote:

Joerg wrote:

ehsjr wrote:

You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?


For a permeability tuned oscillator. It's an experiment to
measure water level, which changes only 3 feet nominal at
the site.

The finished coil is 42" of wire on 46" of PVC. A float
makes the coil ride up and down on a galvanized rod as
the water level changes.

It is accurate to within an inch, with +/- 3" being acceptable,
so that part is good. There is a big (ie 3" change in reading
with a 30F change in ambient) temperature problem to be solved,
but I ran out of warm weather to work on it. Looking for +/- 3"
accuracy between 50 and 100 F.


Can't you run some additional DC through the coil and regulate that so
you get a constant DC resistance through the coil?


Hadn't thought of that. As I recall, there's no DC in the
coil. My notes, circuit, schematic and coil are all buried
in the garage waiting for warm weather. But I'm fairly sure
it's a standard Colpitts with the coil connected to the base,
with no DC path.


Well, you would need a mux. Don't know your frequency but it's not a big
deal.


I'm measuring frequency, which is what changes with temperature
change - I don't remember the direction. As I recall, it makes
an excellent thermometer, implying linear change. Anyway, my
assumption has been that either or both the capacitance and the
inductance are changing with delta T, and I expect the biggest
change is in C, not L. It seems highly probable that the caps
are the biggest source of the delta in Hz. Those assumptions are
what I need to examine next.

BTW - that's just one of the wacko coils I made. :-)
It started out only as a proof of concept thing, but
since I had already Rube Goldberged the "coil winder",
I did a few more of various configurations.


Yep, once you have built a toy it has to be used :-)

--
Regards, Joerg

http://www.analogconsultants.com/

Colpitts Coil
 

"ehsjr" wrote in message
news:EZMhj.5$cz3.2@trnddc06...
ChairmanOfTheBored wrote:
On Thu, 10 Jan 2008 12:57:32 -0800, Peter Bennett
wrote:



How is he going to get three feet of water into his fridge? Also the
float rod?

:-)

Maybe I could move it to the twilight zone?

Ed

That's why I suggested freeze spray.

Colpitts Coil
 

Oppie wrote:
"ehsjr" wrote in message
news:EZMhj.5$cz3.2@trnddc06...
ChairmanOfTheBored wrote:
On Thu, 10 Jan 2008 12:57:32 -0800, Peter Bennett
wrote:



How is he going to get three feet of water into his fridge? Also the
float rod?
:-)

Maybe I could move it to the twilight zone?

Ed

That's why I suggested freeze spray.


Ok, and then the other temperature extreme?

http://web.archive.org/web/200106030...~ghg/grill.jpg

BTW that is someone starting a barbeque really fast.

--
Regards, Joerg

http://www.analogconsultants.com/

Colpitts Coil
 

Joerg wrote:
Oppie wrote:

"ehsjr" wrote in message
news:EZMhj.5$cz3.2@trnddc06...

ChairmanOfTheBored wrote:

On Thu, 10 Jan 2008 12:57:32 -0800, Peter Bennett
wrote:



How is he going to get three feet of water into his fridge? Also the
float rod?

:-)

Maybe I could move it to the twilight zone?

Ed


That's why I suggested freeze spray.


Ok, and then the other temperature extreme?

http://web.archive.org/web/200106030...~ghg/grill.jpg

BTW that is someone starting a barbeque really fast.


:-)

That'll do it!

Ed