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Home > Archive > Electrical Engineering > May 2006 > moderately resistive materials?
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moderately resistive materials?
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| Grant W. Petty 2006-05-15, 7:21 pm |
|
In connection with a prototype design I'm developing for a meteorological
measurement device, I'm looking for a readily available material with the
following physical properties:
1) Moderately resistive -- it will be used for resistive heating by passing
a current through a thin sheet sandwiched between two metal conductors.
Target resistivity should fall in the range 10 to 10**4 m*ohm at
temperatures between 0 and 100 C.
2) A marked increase in resistivity with increasing temperature (this
apparently rules out silicon, for example).
3) Mechanically stable and easy to work with in sheets or disks of order
0.1 mm thickness, 30 cm diameter.
4) Not subject to significant degradation or aging, even at sustained
temperatures near 100 C.
If anyone either knows offhand of a material matching the above description
or can point me to a good tabulation of candidate materials, please let me
know.
thanks
________________________________________
Prof. Grant W. Petty
Atmospheric and Oceanic Sciences
1225 W. Dayton Street
University of Wisconsin-Madison
Madison, WI 53706
gpetty@aos.wisc.edu
Tel: (608) 263-3265
Fax: (608) 262-0166
| |
| tadchem 2006-05-15, 8:21 pm |
|
Grant W. Petty wrote:
> In connection with a prototype design I'm developing for a meteorological
> measurement device, I'm looking for a readily available material with the
> following physical properties:
>
> 1) Moderately resistive -- it will be used for resistive heating by passi=
ng
> a current through a thin sheet sandwiched between two metal conductors.
> Target resistivity should fall in the range 10 to 10**4 m*ohm at
> temperatures between 0 and 100 C.
If you sandwich a resistive material between two conductors, the
current will flow mainly through the conductors, even at low voltage.
Never mind the 'skin effect' of high voltages.
I would want to *insulate* the resistor to force all the current to go
through the resistive material.
> 2) A marked increase in resistivity with increasing temperature (this
> apparently rules out silicon, for example).
>
> 3) Mechanically stable and easy to work with in sheets or disks of order
> 0.1 mm thickness, 30 cm diameter.
>
> 4) Not subject to significant degradation or aging, even at sustained
> temperatures near 100 C.
>
> If anyone either knows offhand of a material matching the above descripti=
on
> or can point me to a good tabulation of candidate materials, please let me
> know.
Start here:
http://en.wikipedia.org/wiki/Platin...nce_thermometer
Note the parabolic form
R(T) =3D R0 * [1 + AT + BT^2]
with A =3D 3.9083 =D7 10-3
This gives a strong positive slope over the linear range. Standard
Pt-100 sensors have 100 ohms resistance at 0=B0 C.
Platinum also meets your other criteria pretty well. as long as you
aren't working in fluorine or aqua regia.
Tom Davidson
Richmond, VA
| |
| Johnny 2006-05-15, 8:21 pm |
|
"Grant W. Petty" <gpetty@aos.wisc.edu> wrote in message
news:Pine.LNX.4.60.0605151511320.15182@cloud.aos.wisc.edu...
>
> In connection with a prototype design I'm developing for a meteorological
> measurement device, I'm looking for a readily available material with the
> following physical properties:
>
> 1) Moderately resistive -- it will be used for resistive heating by
> passing a current through a thin sheet sandwiched between two metal
> conductors. Target resistivity should fall in the range 10 to 10**4 m*ohm
> at temperatures between 0 and 100 C.
>
> 2) A marked increase in resistivity with increasing temperature (this
> apparently rules out silicon, for example).
>
> 3) Mechanically stable and easy to work with in sheets or disks of order
> 0.1 mm thickness, 30 cm diameter.
>
> 4) Not subject to significant degradation or aging, even at sustained
> temperatures near 100 C.
>
> If anyone either knows offhand of a material matching the above
> description or can point me to a good tabulation of candidate materials,
> please let me know.
>
> thanks
>
call up people who make thermisters, Thermotron (sp?) is one.
resistive heating is typically a type of steel wire,or ............. there
is another type that is used too, forgot what name is.
#3 needs a spec. Mechanically Stable ? thermal expansion? how much?
#1 spec, 10 ohms per square ? that is a high value, for metals, you have
a flat thin wafer
| |
| Grant W. Petty 2006-05-15, 8:21 pm |
| | |
| Mark Walter 2006-05-15, 8:21 pm |
| There does not appear to be sufficient info here, or I am missing something.
Most metals exhibit a positive tempco, and they are approx linear (some more
then others)
If the passage of current can be changed to lengthwise I think a metal
film/foil may perform nicely. You may want to look at Minco. They make some
very nice metal film/foil heaters.
M Walter PE
>
> 1) Moderately resistive -- it will be used for resistive heating by
> passing a current through a thin sheet sandwiched between two metal
> conductors. Target resistivity should fall in the range 10 to 10**4 m*ohm
> at temperatures between 0 and 100 C.
>
> 2) A marked increase in resistivity with increasing temperature (this
> apparently rules out silicon, for example).
>
>
> If anyone either knows offhand of a material matching the above
> description or can point me to a good tabulation of candidate materials,
> please let me know.
>
> thanks
>
> ________________________________________
> Prof. Grant W. Petty
> Atmospheric and Oceanic Sciences
> 1225 W. Dayton Street
> university of Wisconsin-Madison
> Madison, WI 53706
>
> gpetty@aos.wisc.edu
> Tel: (608) 263-3265
> Fax: (608) 262-0166
| |
| tadchem 2006-05-15, 10:21 pm |
|
Grant W. Petty wrote:
> On Mon, 15 May 2006, tadchem wrote:
>
>
> To clarify, one conductor is at one potential, the other is at a different
> potential. So the current flow is through (perpendicular to) the resistive
> sheet.
OK. That configuration sounds more like what they called a 'leaky
capacitor' back on the soldering bench.
You need a poor dielectric. Paper runs about 5*10^4 ohm-cm resistivity
according to my old copy of Eshbach's Handbook of Engineering
Fundamentals. This can be 'adjusted' by impregnating the paper with
different liquids. You willl probably need to do a little testing and
literature searching.
Tom Davidson
Richmond, VA
| |
| Grant W. Petty 2006-05-16, 2:21 am |
| On Mon, 15 May 2006, tadchem wrote:
> OK. That configuration sounds more like what they called a 'leaky
> capacitor' back on the soldering bench.
Good analogy. Of course, in this case, the leakiness would be both
deliberate and carefully calibrated.
> You need a poor dielectric. Paper runs about 5*10^4 ohm-cm resistivity
> according to my old copy of Eshbach's Handbook of Engineering
> Fundamentals. This can be 'adjusted' by impregnating the paper with
> different liquids.
I worry that liquid-impregnated paper wouldn't hold up well to continual
heating. So I would probably prefer something graphite-like, or maybe
some composite material, if it exists with the right electrical and thermal
properties.
> You willl probably need to do a little testing and
> literature searching.
Any suggestions concerning reference literature to look at? I'm delving
into areas somewhat outside my normal practical expertise, though I
understand the theory pretty well.
Thanks.
________________________________________
Prof. Grant W. Petty
Atmospheric and Oceanic Sciences
1225 W. Dayton Street
University of Wisconsin-Madison
Madison, WI 53706
gpetty@aos.wisc.edu
Tel: (608) 263-3265
Fax: (608) 262-0166
| |
| Grant W. Petty 2006-05-16, 2:21 am |
|
On Mon, 15 May 2006, Johnny wrote:
>
> #3 needs a spec.
I don't know how to give a spec for this. Basically I'm ruling out anything
that I'd have a hard time handling without breaking or degrading it. For
that matter, I suppose a paste-like goo squeezed between the two conductors
could work, if it won't change properties over time.
> thermal expansion? how much?
TBD. I'd say as long as it's not unusually high it's probably okay.
> #1 spec, 10 ohms per square ? that is a high value,
Yes. I'm thinking something comparable to graphite. In fact, maybe some
kind of conductive graphite composite wafer, if such a thing exists.
________________________________________
Prof. Grant W. Petty
Atmospheric and Oceanic Sciences
1225 W. Dayton Street
University of Wisconsin-Madison
Madison, WI 53706
gpetty@aos.wisc.edu
Tel: (608) 263-3265
Fax: (608) 262-0166
| |
| Rheilly Phoull 2006-05-16, 7:21 am |
| Grant W. Petty wrote:
> In connection with a prototype design I'm developing for a
> meteorological measurement device, I'm looking for a readily
> available material with the following physical properties:
>
> 1) Moderately resistive -- it will be used for resistive heating by
> passing a current through a thin sheet sandwiched between two metal
> conductors. Target resistivity should fall in the range 10 to 10**4
> m*ohm at temperatures between 0 and 100 C.
>
> 2) A marked increase in resistivity with increasing temperature (this
> apparently rules out silicon, for example).
>
> 3) Mechanically stable and easy to work with in sheets or disks of
> order 0.1 mm thickness, 30 cm diameter.
>
> 4) Not subject to significant degradation or aging, even at sustained
> temperatures near 100 C.
>
> If anyone either knows offhand of a material matching the above
> description or can point me to a good tabulation of candidate
> materials, please let me know.
>
> thanks
>
> ________________________________________
> Prof. Grant W. Petty
> Atmospheric and Oceanic Sciences
> 1225 W. Dayton Street
> university of Wisconsin-Madison
> Madison, WI 53706
>
> gpetty@aos.wisc.edu
> Tel: (608) 263-3265
> Fax: (608) 262-0166
Dont suppose a peltier array would be any help ??
--
Regards ......... Rheilly Phoull
| |
|
|
"Grant W. Petty" <gpetty@aos.wisc.edu> wrote in message
news:Pine.LNX.4.60.0605151511320.15182@cloud.aos.wisc.edu...
>
> In connection with a prototype design I'm developing for a meteorological
> measurement device, I'm looking for a readily available material with the
> following physical properties:
>
> 1) Moderately resistive -- it will be used for resistive heating by
passing
> a current through a thin sheet sandwiched between two metal conductors.
> Target resistivity should fall in the range 10 to 10**4 m*ohm at
> temperatures between 0 and 100 C.
>
> 2) A marked increase in resistivity with increasing temperature (this
> apparently rules out silicon, for example).
>
> 3) Mechanically stable and easy to work with in sheets or disks of order
> 0.1 mm thickness, 30 cm diameter.
>
> 4) Not subject to significant degradation or aging, even at sustained
> temperatures near 100 C.
>
> If anyone either knows offhand of a material matching the above
description
> or can point me to a good tabulation of candidate materials, please let me
> know.
>
> thanks
>
> ________________________________________
> Prof. Grant W. Petty
> Atmospheric and Oceanic Sciences
> 1225 W. Dayton Street
> university of Wisconsin-Madison
> Madison, WI 53706
>
> gpetty@aos.wisc.edu
> Tel: (608) 263-3265
> Fax: (608) 262-0166
>
You might pose your question on sci.materials.
Mike
| |
| Grant W. Petty 2006-05-16, 12:21 pm |
| On Tue, 16 May 2006, Rheilly Phoull wrote:
>
> Dont suppose a peltier array would be any help ??
I don't know what that is ... is it related to the Peltier effect?
________________________________________
Prof. Grant W. Petty
Atmospheric and Oceanic Sciences
1225 W. Dayton Street
University of Wisconsin-Madison
Madison, WI 53706
gpetty@aos.wisc.edu
Tel: (608) 263-3265
Fax: (608) 262-0166
| |
| operator jay 2006-05-17, 2:21 am |
|
"Johnny" <nospam@nospam.com> wrote in message
news:44690170$0$80513$892e7fe2@authen.yellow.readfreenews.net...
>
> "Grant W. Petty" <gpetty@aos.wisc.edu> wrote in message
> news:Pine.LNX.4.60.0605151511320.15182@cloud.aos.wisc.edu...
meteorological[color=darkred]
the[color=darkred]
m*ohm[color=darkred]
>
> call up people who make thermisters, Thermotron (sp?) is one.
> resistive heating is typically a type of steel wire,or .............
there
Nichrome?
<http://www.google.ca/search?hl=en&q=nichrome>
> is another type that is used too, forgot what name is.
> #3 needs a spec. Mechanically Stable ? thermal expansion? how much?
> #1 spec, 10 ohms per square ? that is a high value, for metals, you
have
> a flat thin wafer
>
>
| |
| Roy L. Fuchs 2006-05-17, 4:21 am |
| On 15 May 2006 15:31:01 -0700, "tadchem" <tadchem@comcast.net> Gave
us:
> even at low voltage.
>Never mind the 'skin effect' of high voltages.
Skin effect is a function of frequency, not voltage.
It is just easier to prove in higher voltage settings.
| |
| jalegris@sympatico.ca 2006-05-19, 11:21 am |
|
Grant W. Petty wrote:
> In connection with a prototype design I'm developing for a meteorological
> measurement device, I'm looking for a readily available material with the
> following physical properties:
>
> 1) Moderately resistive -- it will be used for resistive heating by passing
> a current through a thin sheet sandwiched between two metal conductors.
> Target resistivity should fall in the range 10 to 10**4 m*ohm at
> temperatures between 0 and 100 C.
>
> 2) A marked increase in resistivity with increasing temperature (this
> apparently rules out silicon, for example).
>
> 3) Mechanically stable and easy to work with in sheets or disks of order
> 0.1 mm thickness, 30 cm diameter.
>
> 4) Not subject to significant degradation or aging, even at sustained
> temperatures near 100 C.
>
> If anyone either knows offhand of a material matching the above description
> or can point me to a good tabulation of candidate materials, please let me
> know.
>
> thanks
>
Perhaps you can get some of the the material used in self-resetting
fuses: a conductive polymeric concoction with a non-linear PTC.
http://www.circuitprotection.com/polyswitch.asp
http://www.circuitprotection.com/06...undamentals.pdf
--
Joe Legris
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