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#1
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Colpitts Coil
You call that a coil? That's not a coil.
*This* is a coil! Ed |
#2
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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/ |
#3
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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 Voice480)460-2350 | | | E-mail Address at Website Fax480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | America: Land of the Free, Because of the Brave |
#4
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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 |
#5
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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 |
#6
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Colpitts Coil
"ehsjr" wrote in message news:3qihj.3848$K%6.3695@trndny04... Joerg wrote: ehsjr wrote: You call that a coil? That's not a coil. *This* is a coil! No, it's a petunia. Or whatever. (I am not a botanical expert) So, what's that super-stretch edition of coil for? For a permeability tuned oscillator. It's an experiment to measure water level, which changes only 3 feet nominal at the site. The finished coil is 42" of wire on 46" of PVC. A float makes the coil ride up and down on a galvanized rod as the water level changes. It is accurate to within an inch, with +/- 3" being acceptable, so that part is good. There is a big (ie 3" change in reading with a 30F change in ambient) temperature problem to be solved, but I ran out of warm weather to work on it. Looking for +/- 3" accuracy between 50 and 100 F. Ed Where do you think the temperature effect is coming in - the oscillator portion or the coil? Some freeze spray is usually a good way to find gross effects of temperature. Does the inductance change also with temperature? An inductance bridge would be helpful here. How about using a LVDT approach instead? |
#7
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Colpitts Coil
Oppie wrote:
"ehsjr" wrote in message news:3qihj.3848$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 |
#8
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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. |
#9
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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 |
#10
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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/ |
#11
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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 |
#12
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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/ |
#13
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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 |
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