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Date: Thu, 14 Nov 2002 20:06:04 -0500
From: "Raymond E. Rogers"
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Subject: Re: Temperature Measurement Stability
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Thanks Bill, comments embedded
Bill Sloman wrote:
> RS Components stock DIN B/3 parts, which is to say +/-0.1C
> Hart Scientitic will sell you a calibrated Pt100 four wire sensor assembly
> good to +/-0.02C for a hundred dollars or so, and the electronics to read it
> to that accuracy for about $1500. We use a Thurlby-Thandar 1906 computing
> multimeter as a four-wire ohmeter, and convert the resistances to
> temperature by solving the quadratic in Excel - not quite as good, but much
We bought a $4000 NIST traceable thermsitor Thermometer that I am going
to use for calibration. I have several other thermal problems and
wanted something reliable (if ungainly).
> For a more comprehensive discussion of temperature stabilisation near room
> temperature, see A W Sloman, Paul Buggs, James Molloy and Douglas Stewart "A
> microcontroller-based driver to stabilize the temperature of an optical
> stage to within 1mK inthe range 0-38C, using a Peltier heat pump and a
> thermistor sensor" published in Measurement Science and Technology volume
> 7,. pages 1653-64 (1996), which is not only useful in its own right (if I
> say so myself) but cites about a dozen earlier papers with useful content.
> The +/-0.2C Betatherm thermistors we used are claimed to drift less than
> 11mK per year at 75C. Yellow Springs Instruments offers some +/-0.05C
> tolerance parts that ought to be even more stable, and are available off the
> shelf from Newark - they have 16 of the 10k at 25C part 46006 (stock no
> 46F3197) for $47.60 each.
Yes we bought some from YSI that in fact have data to back up the
stability claims; and they are costing about $100. Okay for research
but probably to much for production.
> A couple of the papers we cited achieved much better than millidegree
> stability. Larsen's classic paper describes a 50 microdegree stability water
> bath built around a 500R platinum resistance sensor, and Priel got down to
> +/-3.5 microdegrees with a Fenwall thermistor sensor. Preil complained that
> dissipating more than 16uW in his sensor produced appreciable long term
> drift, but probably within the +/0.03C range asked for by the original
> Interchangeable thermistors from reputable suppliers should be pretty
> stable. Their great advantage is their high sensitivity - about -4% per
I will make a calibration fixture. We can spend money on capitol
equipment but the shipped instrument must be cheap (relatively
speaking). I gave up on interchangability.
> degree C, compared with +0.39% for Pt100 and Pt1000 sensors. This not only
> makes the job of the measuring electronics much easier, but lets you get
> away with cheaper and more easily accessible current-setting resistors and
> so forth. A DIN B/3 Pt100 is a +/-0.04% resistor, and using anything less
> than $10 Vishay 0.01% resistor throws away most of the accuracy you've paid
> for. The YSI +/-0.05C thermistors are +/-0.2% resistors ...
> The National Semiconductor LM35 semiconductor temperature sensor is a bit
> noiser than a good thermistor or a platinum resistance sensor, but even
> easier to use. My office mate at Nijmegen University used the metal-packaged
> part for some millidegree stability temperature calibration baths and was
I found the national data sheets .1 - .2 degC/khr , not good enough.
> very happy with their long term stability. The Dallas parts may be suspect -
> we had a posting here a couple of years ago about some nasty temperature
> drifts that turned out to be humidity driven. Water vapour was getting
> through the plastic packaging. I'm sure that the problem has been solved by
> now, at least at the level of performance guaranteed on the data sheet.
I have yet to find the Dallas drift specs. I will try to look up your
paper and follow the references.
Maybe I can use your paper as an authoritative reference instead of the
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