Temperature sensing for room temperature SQUIDs

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Lets say that I needed to sense temperatures around 0C to 50C without
introducing any magnetics (or at least no DC field), any Ideas?

All thermistors appear to be magnetic so I can't use the thermistor
fed with AC.

Re: Temperature sensing for room temperature SQUIDs




MooseFET wrote:

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A conventional alcohol thermometer + optical readout via the fiberoptic
line?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com



Re: Temperature sensing for room temperature SQUIDs


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I hadn't thought of that.  It is an interesting idea because it also
removes the copper wires completely.



Re: Temperature sensing for room temperature SQUIDs



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How about a mirror mounted on a bimetalic strip?

What sort of metals are used on typical bimetalic?  Can you get
one that is sufficiently non-magnetic?  Or make one out of something
you like?

--
These are my opinions, not necessarily my employer's.  I hate spam.


Re: Temperature sensing for room temperature SQUIDs


On Sep 14, 12:29 am, hal-use...@ip-64-139-1-69.sjc.megapath.net (Hal
Murray) wrote:
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One of the two or perhaps both metals will be magnetic.  The only
copper it seems I can trust is made thanks to the audio nuts.


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Cheap stuff and other cheap stuff.  They are optimized for low price.


  Can you get
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Re: Temperature sensing for room temperature SQUIDs


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You can make a 'bimetal' strip out of two kinds of plastic.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
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Re: Temperature sensing for room temperature SQUIDs


On Sep 14, 3:05 am, Phil Hobbs
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Cute idea.  The all optical nature of it appeals to me in a different
application.

If I can use a fiber to measure the deflection, it would be an all non
conductive connection.

I already have a method for measuring the field with no electricals.
It involves three light pipes.  Adding a couple more wouldn't be a bad
thing to do.  The active can be inside a sealed glass with a vacuum.


Re: Temperature sensing for room temperature SQUIDs



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Could you build your own out of materials you like?

It doesn't have to be two metals stuck together.  That just
gets a lot of change for a given temperature.  How about gluing
a mirror across 2 blocks of xxx and yyy?  Brass and plastic?
Plastic and glass?

That won't move much.  How stable is whatever you would be
mounting it on?  Ahh...  Build two of them in opposite
directions.  Then don't measure the position of the reflected
dot but the difference in position between two dots.

--
These are my opinions, not necessarily my employer's.  I hate spam.


Re: Temperature sensing for room temperature SQUIDs


On Sep 14, 8:50A0%am, hal-use...@ip-64-139-1-69.sjc.megapath.net (Hal
Murray) wrote:
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This is basically the bimetal spring idea.  I can't use brass
but perhaps two plasics may be worth a look.

Re: Temperature sensing for room temperature SQUIDs



 >Re: Temperature sensing for room temperature SQUIDs

April 1 came early?

How about a back-to-back dual diode with AC drive?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
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Re: Temperature sensing for room temperature SQUIDs


On Sep 13, 6:54 am, Phil Hobbs
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Two problems:

1) just try to find a diode that really is nonmagnetic.  I bought some
"nonmagnetic diodes" intended for MRI use.  They are magnetic.  They
read about 25nT at 2 inches.

2) The rectified current in the diodes flow in a little circle working
like a little dipole.

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Re: Temperature sensing for room temperature SQUIDs


On a sunny day (Sun, 13 Sep 2009 07:46:05 -0700 (PDT)) it happened MooseFET

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Would it be incorrect to think that making an opposite current next to it,
would cancel that magnetic field?
Like a reverse wire loop in series (sort of folded back) directly above it?

Re: Temperature sensing for room temperature SQUIDs


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Would you tell us what your real application is?  (There's no such thing
as quantum interference at macroscopic scales at room temperature, nor
are there superconductors there, so all that's left of the 'squid' is
'device'.  Or maybe it's for oceanography?

That would make it a bit easier to understand what your actual
requirements are.  (5 nA going around a 1 mm diameter loop is a pretty
small magnetic moment.)

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal
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Re: Temperature sensing for room temperature SQUIDs


On Sep 14, 12:42 am, Phil Hobbs
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Ok it is just a "device".  The active area is about 3mm in size.  I
want to know the temperature of the active part or the assembly
without creating a DC field greater than about 0.3nT.  Because of the
physics involved frequencies above several KHz, are not seen by the
sensor.

I only really need to know the temperature to an accuracy of about
0.5C.
I can wait a large fraction of a second for the measurement so very
low currents are ok.

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Re: Temperature sensing for room temperature SQUIDs


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Over what range of temperature(s) do you need it to work?

Some of the LCD thermal paints are non-magnetic and accurate to 0.5C
with a relatively slow response time. The other way would be to put the
sensor into a temperature controlled flow of dry nitrogen, argon or
helium. The latter gives the best thermal transfer.

Or are you saying the part dissipates real amounts of power?

Regards,
Martin Brown

Re: Temperature sensing for room temperature SQUIDs


On Sat, 12 Sep 2009 15:30:10 -0700 (PDT), MooseFET

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Platinum or copper RTD, very low level DC or AC excitation

Fiberoptic thermometer

Infrared

Diode, at pulsed nanoamp currents

Varicaps have huge dC/dT

FR4, about 900 PPM/K capacitance TC

IC sensor, LM45, LM71


What's a room temperature SQUID? The "S" stands for "superconducting."

John


Re: Temperature sensing for room temperature SQUIDs


On Sep 13, 6:59 am, John Larkin
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Do you know of a maker of nonmagnetic ones?

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Vladimir beat you here.

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This will be a bit costly because it would need calibration. Won't it?

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This is why I bought the "nonmagnetic diodes" that turned out to be
magnetic.

Voltronics as an "extensive line of nonmagnetic diodes" which turns
out to be exactly one type of back to back Schottky.  I pointed the
issue out to them.  They have neither introduced another type of diode
nor fixed the wording the last time I looked.  I still haven't ruled
them out because it wasn't their diode that turned out to be magnetic.
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Re: Temperature sensing for room temperature SQUIDs


On Sun, 13 Sep 2009 07:54:41 -0700 (PDT), MooseFET

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No, but all it takes is platinum and copper, so it should be available
somewhere. Or just all-copper, a small coil of fine wire with maybe a
4-wire connection.

Cryo-con sells an RTD with platinum leads, no nickel. I think Omega
may, too. Try Lakeshore Cryo, too.

Copper is faintly paramagnetic, so messes up fields at the 1e-9 sort
of levels. The NMR guys plate their copper antennas with a secret
sauce to null that out.

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I meant the kind with a temperature-sensitive fluorescent end. They
input short-wave light and bounce back a temperature-dependent
spectrum. Not cheap.

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Maybe they have lots of them.


  I pointed the
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Sounds like a thermocouple is the best idea so far.

John


Re: Temperature sensing for room temperature SQUIDs


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You can excite a platinum resistance thermometer with 15kHz AC and
read the temperature to an accuracy of a few microdegrees if you try
hard enough. You'd need a bifilar-wound transformer in your Blumlein
bridge to do that well, but getting to +/-0.5C would be less
demanding.

--
Bill Sloman, Nijmegen


Re: Temperature sensing for room temperature SQUIDs


On Sun, 13 Sep 2009 14:32:38 -0700 (PDT), the renowned Bill Sloman

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That's an awfully high frequency for an AC bridge of ppm-level
accuracy, given the approximately PTAT change in resistance of a noble
metal RTD. I'd fear going much beyond the hundreds of Hz due to stray
capacitances and such like. If it was not a problem, I'd suggest
synching it to the modulation frequency of the SQUIDs (usually 100kHz
or higher, but they're working to a null).



Best regards,
Spehro Pefhany
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"it's the network..."                          "The Journey is the reward"
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