Temperature sensing for room temperature SQUIDs

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

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

April 1 came early?

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

Cheers

Phil Hobbs

-- Dr Philip C D Hobbs Principal ElectroOptical Innovations

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

Thermistors are resistive.

Why do you think they are magnetic ?

Also, why does it matter ?

don

Two problems:

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

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

Probably because they stick to a magnet. Lots of parts do.

Some parts are repelled by a magnet, which can be just as bad a problem.

John

Do you know of a maker of nonmagnetic ones?

Vladimir beat you here.

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

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.

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

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?

I know they are magnetic. I have measured several types They are a strange sort of metal oxide semiconductor thing. Among the oxides are magnetic ones

It will cause a large error in the measured magnetic field.

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

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.

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

Maybe they have lots of them.

I pointed the

Sounds like a thermocouple is the best idea so far.

John

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?

Kovar leads, for the glass bead type.

Cheers

Phil Hobbs

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

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

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.

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

Can you get

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

Cheers

Phil Hobbs

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.

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