Greetings,

I'm working up a demonstration of an antique electronic temperature
controller which needs a sensor with a PTC of about 5 to 6 ohms/degree F
average (at 20 degrees C); nickel-iron resistance wire fits the bill
fairly well, and I would like to find a coil on a low-mass substrate,
like ceramic, of roughly 1150 ohms at 20 degrees C, hopefully no more
than a few inches long (up to 5 inches is OK). I have some resistance
wire salvaged from old soldering iron heater cores, but its gauge is
a bit large such that to get 1150 ohms would require quite a lot of it
on a rather large form.

Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range, or
for sensing, that might come in at around 1150 ohms, so that I might
avoid a tedious winding of hair-fine wire under magnification.
Surprisingly (to me), my cannibalization of some 10 Watt heating tools
(like hot melt glue guns) revealed not resistance wire, but some form
of semiconductor with a NTC (isn't thermal runaway an issue here?).

Michael

In article t, msg wrote:
Greetings,

I'm working up a demonstration of an antique electronic temperature
controller which needs a sensor with a PTC of about 5 to 6 ohms/degree F
average (at 20 degrees C); nickel-iron resistance wire fits the bill
fairly well, and I would like to find a coil on a low-mass substrate,
like ceramic, of roughly 1150 ohms at 20 degrees C, hopefully no more
than a few inches long (up to 5 inches is OK). I have some resistance
wire salvaged from old soldering iron heater cores, but its gauge is
a bit large such that to get 1150 ohms would require quite a lot of it
on a rather large form.

Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range, or
for sensing, that might come in at around 1150 ohms, so that I might
avoid a tedious winding of hair-fine wire under magnification.
Surprisingly (to me), my cannibalization of some 10 Watt heating tools
(like hot melt glue guns) revealed not resistance wire, but some form
of semiconductor with a NTC (isn't thermal runaway an issue here?).


I don't know your linearity requirments. I might suggest using a thermsiter.
The only thing I know of, 1 K are hard to find, are some SMT thermisters.
I had used one soldeing leads on to it. Typical 1097 ohms @ 25C
You can add series resistanc eto calibrate scale. Linearity might
be off which is gain of device.

http://www.vishay.com/docs/28762/28762.pdf



greg

msg wrote:
Greetings,

I'm working up a demonstration of an antique electronic temperature
controller which needs a sensor with a PTC of about 5 to 6 ohms/degree F
average (at 20 degrees C); nickel-iron resistance wire fits the bill
fairly well, and I would like to find a coil on a low-mass substrate,
like ceramic, of roughly 1150 ohms at 20 degrees C, hopefully no more
than a few inches long (up to 5 inches is OK). I have some resistance
wire salvaged from old soldering iron heater cores, but its gauge is
a bit large such that to get 1150 ohms would require quite a lot of it
on a rather large form.

Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range, or
for sensing, that might come in at around 1150 ohms, so that I might
avoid a tedious winding of hair-fine wire under magnification.
Surprisingly (to me), my cannibalization of some 10 Watt heating tools
(like hot melt glue guns) revealed not resistance wire, but some form
of semiconductor with a NTC (isn't thermal runaway an issue here?).

Michael
Why not use the filament of a Vacuum Tube ?
Try a battery operated one like 1B???
Or one like 12AX??
Might have to break the Glass envelope
This would solve all the mounting problems
How about a 25 watt 110 Volt Light Bulb?

I have often wondered how these might work in a Thermal Conductivity
Vacuum Pressure Gage ?

Yukio YANO

On Mar 2, 9:28*am, msg wrote:

I'm working up a demonstration of an antique electronic temperature
controller which needs a sensor with a PTC of about 5 to 6 ohms/degree F
average (at 20 degrees C); nickel-iron resistance wire fits the bill
fairly well, and I would like to find a coil on a low-mass substrate,
like ceramic, of roughly 1150 ohms at 20 degrees C

What alloy, exactly, of 'nickel-iron' do you have in wire form?
5.5 ohms/F at 1150 ohms is about 0.5% per F, 0.9% per C.
That's rather high (0.3% per C at room temperature is 'normal'
for pure metals like Cu). Usually, alloys have LOWER
temperature coefficient than pure metals.

Chrome-nickel (like 80% Ni/20% Cr, "Chromel A") heater
wire comes in at 0.007% per F.

In article , (GregS) wrote:
In article t, msg
wrote:
Greetings,

I'm working up a demonstration of an antique electronic temperature
controller which needs a sensor with a PTC of about 5 to 6 ohms/degree F
average (at 20 degrees C); nickel-iron resistance wire fits the bill
fairly well, and I would like to find a coil on a low-mass substrate,
like ceramic, of roughly 1150 ohms at 20 degrees C, hopefully no more
than a few inches long (up to 5 inches is OK). I have some resistance
wire salvaged from old soldering iron heater cores, but its gauge is
a bit large such that to get 1150 ohms would require quite a lot of it
on a rather large form.

Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range, or
for sensing, that might come in at around 1150 ohms, so that I might
avoid a tedious winding of hair-fine wire under magnification.
Surprisingly (to me), my cannibalization of some 10 Watt heating tools
(like hot melt glue guns) revealed not resistance wire, but some form
of semiconductor with a NTC (isn't thermal runaway an issue here?).


I don't know your linearity requirments. I might suggest using a thermsiter.
The only thing I know of, 1 K are hard to find, are some SMT thermisters.
I had used one soldeing leads on to it. Typical 1097 ohms @ 25C
You can add series resistanc eto calibrate scale. Linearity might
be off which is gain of device.

http://www.vishay.com/docs/28762/28762.pdf



No words from the OP. ??

Are you worried about self heating ??

greg

Yukio YANO wrote:

msg wrote:

snip

Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range, or
for sensing, that might come in at around 1150 ohms

snip

Why not use the filament of a Vacuum Tube ?
Try a battery operated one like 1B???
Or one like 12AX??
Might have to break the Glass envelope
This would solve all the mounting problems
How about a 25 watt 110 Volt Light Bulb?

I have often wondered how these might work in a Thermal Conductivity
Vacuum Pressure Gage ?

Thanks for your reply.

I suppose one could work up an R-T chart for various filaments, however
for my application, I need more sensitivity than tungsten and other
conventional filaments could provide. It would be fun to test a filament
and/or heater from a 117V tube and also various low wattage light bulbs
in a temp bridge, but I do need to approximate the nickel-iron RTC of
about .00518 ohm/ohm/degC.

Michael

GregS wrote:

msg wrote:


snip
Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range, or
for sensing, that might come in at around 1150 ohms

snip



I don't know your linearity requirments. I might suggest using a thermsiter.
The only thing I know of, 1 K are hard to find, are some SMT thermisters.
I had used one soldeing leads on to it. Typical 1097 ohms @ 25C
You can add series resistanc eto calibrate scale. Linearity might
be off which is gain of device.

Thanks for your reply.

I had originally hoped to find a compatible PTC thermistor but decided that
I probably would find it easier to scrounge enough nickel-iron wire to do
the job, as that was what the controller originally expected for its sensor
and is matched to its RTC.

Michael

whit3rd wrote:

On Mar 2, 9:28 am, msg wrote:


I'm working up a demonstration of an antique electronic temperature
controller which needs a sensor with a PTC of about 5 to 6 ohms/degree F
average (at 20 degrees C); nickel-iron resistance wire fits the bill
fairly well, and I would like to find a coil on a low-mass substrate,
like ceramic, of roughly 1150 ohms at 20 degrees C


What alloy, exactly, of 'nickel-iron' do you have in wire form?
5.5 ohms/F at 1150 ohms is about 0.5% per F, 0.9% per C.
That's rather high (0.3% per C at room temperature is 'normal'
for pure metals like Cu). Usually, alloys have LOWER
temperature coefficient than pure metals.

Chrome-nickel (like 80% Ni/20% Cr, "Chromel A") heater
wire comes in at 0.007% per F.


I was hoping that folks could recollect some consumer or industrial
items to cannibalize for various nickel-iron alloy wires to try, such
as curling irons (of a certain vintage), kitchen appliances, etc.
I have some nichrome wire in different gauges but nothing fine enough
to make 1k to 2k ohms in a small space yet. The published data for the
RTC of (unspecified alloy) nickel-iron I took from the white paper
by Minco: "Resistance Thermometry: Principles and Applications"
http://www.minco.com/download-media.aspx?id=2284 as .00527 ohm/ohm/deg C.

The control range is about 17 deg. C and delta R is 175 ohms over that
range; recalculating for nickel-iron shows I should be using a sensor
of about 1950 ohm at 20 deg. C; my previous value of 1150 ohms was
derived by measurement using a variable resistor to balance the bridge.
Evidently component aging (dates from 1946) are to blame and I will need
to recalibrate the bridge to use a 2k ohm sensor.

Michael

msg wrote:

Greetings,

I'm working up a demonstration of an antique electronic temperature
controller which needs a sensor with a PTC of about 5 to 6 ohms/degree F
average (at 20 degrees C); nickel-iron resistance wire fits the bill
fairly well, and I would like to find a coil on a low-mass substrate,
like ceramic, of roughly 1150 ohms at 20 degrees C, hopefully no more
than a few inches long (up to 5 inches is OK). I have some resistance
wire salvaged from old soldering iron heater cores, but its gauge is
a bit large such that to get 1150 ohms would require quite a lot of it
on a rather large form.

Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range...

snip

I disassembled a wooden-handled curling iron (unknown mfg, made in USA
perhaps in the 1940s or 50s) and discovered only an eight inch length
of heater cable doubled up and crimped to twin-lead line cord.

I would very much appreciate some recollections of appliances which
contain lengths of fine-gauge resistance wire.

Regards,

Michael

In article t,
msg wrote:

Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range, or
for sensing, that might come in at around 1150 ohms, so that I might
avoid a tedious winding of hair-fine wire under magnification.

Michael-

Look for a 5 or 10 watt, 1200 Ohm wire wound resistor at Radio Shack.
Perhaps its temperature coefficient would not be what you need, but it
would give you a point of reference.

I wonder if a very old wire wound resistor from someone's junk box,
would be more like what you need?

Fred

Fred McKenzie wrote:

In article t,
msg wrote:


Perhaps someone has recollections of small assemblies of resistance wire
either used for heating, in the 10 to 12 Watt (at 120 VAC) range, or
for sensing, that might come in at around 1150 ohms, so that I might
avoid a tedious winding of hair-fine wire under magnification.


Michael-

Look for a 5 or 10 watt, 1200 Ohm wire wound resistor at Radio Shack.
Perhaps its temperature coefficient would not be what you need, but it
would give you a point of reference.

I wonder if a very old wire wound resistor from someone's junk box,
would be more like what you need?

Perhaps some 'antique' wirewound resistors would have a useful R-T
characteristic; I tried some post-war types and they seem to be
somehow temp compensated and not very sensitive, but I have not by
any means exhausted the subset of potential candidates that deserve
to be tested. I assumed that the alloys used for (modern) wirewound
resistors would also be chosen to reduce temperature sensitivity.

Michael