Ultra low temp measuring techniques

[Paul]

Hi,

I need to measure ultra low temperature changes on a 0.5mm x 0.5mm
piece near room temperatures. During "off" state the temperature of
the piece will remain at room temperature. During "on" state the
temperature of the piece will change. Normally I would use two 201
package/case thermistor chips, placing one on the piece and the other
on a neutral area to measure a temp gradient, but I need to measure
down to 1e-7 Kelvin gradient. I've only achieved down to 1e-6 temp
gradient using thermistors with a sampling method by taking thousands
of measurements. Does anyone have recommendations how to achieve this
task? Perhaps a chemical that's highly sensitive to temperature that
would change in hue or reflectivity. I could use a photodiode diode to
detect slight changes in hue to reflectivity. Or perhaps a thermistor
that has less noise.

Thanks,
Paul

 

[[email protected]]

Hi,

I need to measure ultra low temperature changes on a 0.5mm x 0.5mm
piece near room temperatures. During "off" state the temperature of
the piece will remain at room temperature. During "on" state the
temperature of the piece will change. Normally I would use two 201
package/case thermistor chips, placing one on the piece and the other
on a neutral area to measure a temp gradient, but I need to measure
down to 1e-7 Kelvin gradient. I've only achieved down to 1e-6 temp
gradient using thermistors with a sampling method by taking thousands
of measurements. Does anyone have recommendations how to achieve this
task? Perhaps a chemical that's highly sensitive to temperature that
would change in hue or reflectivity. I could use a photodiode diode to
detect slight changes in hue to reflectivity. Or perhaps a thermistor
that has less noise.

Johnson noise limits the sensitivity you can get out of a thermistor
(or a plantinum resistance sensor) to about 1e-6 Kelvin at room
temperature.

I first came acreoss the relationship in Larsens's classic paper

Larsen N T 1968 Rev. Sci. Instrum. 39 1–12

and published a comment that discussed the implications of the
relationship some ten years later

Sloman A W 1978 J. Phys. E: Sci. Instrum. 11 967–8

You may need to think this one out again.

 

[Androcles]

Hi,

I need to measure ultra low temperature changes on a 0.5mm x 0.5mm
piece near room temperatures. During "off" state the temperature of
the piece will remain at room temperature. During "on" state the
temperature of the piece will change. Normally I would use two 201
package/case thermistor chips, placing one on the piece and the other
on a neutral area to measure a temp gradient, but I need to measure
down to 1e-7 Kelvin gradient. I've only achieved down to 1e-6 temp
gradient using thermistors with a sampling method by taking thousands
of measurements. Does anyone have recommendations how to achieve this
task? Perhaps a chemical that's highly sensitive to temperature that
would change in hue or reflectivity. I could use a photodiode diode to
detect slight changes in hue to reflectivity. Or perhaps a thermistor
that has less noise.

Thanks,
Paul

From what you've said already I doubt I can contribute much,
all I can suggest is that you eliminate the noise. The difficulty
is distinguishing unwanted electrical noise from the thermal noise
that you want to measure.
Have you considered an RTD?
http://en.wikipedia.org/wiki/Resistance_temperature_detector

 

[[email protected]]

Hi,

I need to measure ultra low temperature changes on a 0.5mm x 0.5mm
piece near room temperatures. During "off" state the temperature of
the piece will remain at room temperature. During "on" state the
temperature of the piece will change. Normally I would use two 201
package/case thermistor chips, placing one on the piece and the other
on a neutral area to measure a temp gradient, but I need to measure
down to 1e-7 Kelvin gradient. I've only achieved down to 1e-6 temp
gradient using thermistors with a sampling method by taking thousands
of measurements. Does anyone have recommendations how to achieve this
task? Perhaps a chemical that's highly sensitive to temperature that
would change in hue or reflectivity. I could use a photodiode diode to
detect slight changes in hue to reflectivity. Or perhaps a thermistor
that has less noise.

Thanks,
Paul

Google "Sub-microkelvin measurement"

Tom Davidson
Richmond, VA

 

[Uncle Al]

Hi,

I need to measure ultra low temperature changes on a 0.5mm x 0.5mm
piece near room temperatures. During "off" state the temperature of
the piece will remain at room temperature. During "on" state the
temperature of the piece will change. Normally I would use two 201
package/case thermistor chips, placing one on the piece and the other
on a neutral area to measure a temp gradient, but I need to measure
down to 1e-7 Kelvin gradient. I've only achieved down to 1e-6 temp
gradient using thermistors with a sampling method by taking thousands
of measurements. Does anyone have recommendations how to achieve this
task? Perhaps a chemical that's highly sensitive to temperature that
would change in hue or reflectivity. I could use a photodiode diode to
detect slight changes in hue to reflectivity. Or perhaps a thermistor
that has less noise.

Convert 10^(-7) K to kilocal/mole, eV, cm^(-1)... Even if you could
do it with temp-modulated Faraday rotation, how would you prevent the
interrogating beam from swamping the signal?

If the temp gradient deforms the substrate (coefficient of thermal
expansion),

"Ultrasensitive Beam Deflection Measurement via Interferometric Weak
Value Amplification"
Phys. Rev. Lett. 102, 173601 (2009)
http://physics.aps.org/articles/v2/32
<http://physics.aps.org/pdf/10.1103/PhysRevLett.102.173601.pdf>

 

[Paul]

Convert 10^(-7) K to kilocal/mole, eV, cm^(-1)...  Even if you could
do it with temp-modulated Faraday rotation, how would you prevent the
interrogating beam from swamping the signal?

If the temp gradient deforms the substrate (coefficient of thermal
expansion),

"Ultrasensitive Beam Deflection Measurement via Interferometric Weak
Value Amplification"
Phys. Rev. Lett. 102, 173601 (2009)http://physics.aps.org/articles/v2/32
<http://physics.aps.org/pdf/10.1103/PhysRevLett.102.173601.pdf>

Thank for all helpful advice. Bill's reference to a 1e-6 Kelvin
limitation appears to match my 1e-6 K limit. Uncle Al and Robert Baer
made a valid point regarding the sensing device interfering with the
measurements. The only idea that comes to mind is perhaps to measure
the blackbody radiation emitting from the DUT; i.e., a highly
sensitive non-contact FIR thermal chip. Personally I've never heard of
such sensitivity from FIR thermal chips. Perhaps several hours worth
of sampling in a shielded controlled system could achieve sub-
microkelvin measurement?

Regards,
Paul

 

[[email protected]]

Thank for all helpful advice. Bill's reference to a 1e-6 Kelvin
limitation appears to match my 1e-6 K limit. Uncle Al and Robert Baer
made a valid point regarding the sensing device interfering with the
measurements.

The 1e-6 Kelvin limit isn't absolute; it's just the way the numbers
work out in typical situations with resistance sensors. In my comment

Sloman A W 1978 J. Phys. E: Sci. Instrum. 11 967–8

I discussed how you might lower the Johnson noise limit. It involves
dissipating appreciable power in the sensor, which quantifies the
point made by Uncle Al and Robert Baer.