De-Macro'd Vishay Thermistor Data

Jan 17, 2018 4 Replies

That "risky click" thread reminded me of something else:



Vishay publishes data for all their thermistors ... in an Excel spreadsheet, that's not actually a spreadsheet, well not just, but mostly a /VBA application/ that runs on top of the spreadsheet. Not even signed.



Risky click of the day right there. I don't recommend it. It's terrible. Fortunately it didn't seem to contain malicious code, but eugh...



I took it upon myself to strip away all the junk. It turns out, they wrote a quite serviceable spreadsheet underlying everything. You enter a part number, and see if one sheet or another turns up a match. You get the part specs, all the Steinhart-Hart parameters, and a table of R(T) if you don't want to faff with the parameters. Or you can look up the coefficients in the master table, which looks like it's straight from their corporate database. Very convenient; if only they had provided it in usable form in the first place!



Teaser:

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Unfortunately, I can't link a direct download. Request via e-mail.



P.S. A reminder how nasty VBA is. It can hook anything on the system; it's a proper application, not even a sandbox like JS in your browser. For example, one of the steps in the procedure involved temporarily intercepting a user32.dll call...



Tim


Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/

Good work, Tim! Thanks!

Thanks, - Win

I took my Beta value and plugged it into a couple of online thermistor calculators, which agreed. One of them did the voltage divider math for me. (Resistor to +3 Vref, thermistor to ground, into ADC using that same vref.)

The 12 voltage points went into Excel for the polynomial.

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This will be to control the fan and do some temperature comps in an instrument, so it doesn't need to be super accurate.

I'm thinking about using an up/down counter as the fan control algorithm. Increment or decrement an integer by N if the temp is below or above some target, and map the integer into the 24V fan voltage. That is simple and not acoustically dramatic. Small N might take a minute to slew the fan voltage.

John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com

We use Yellow springs (YSI) thermsitors, last time I went to their web site all I could find was an equation. With several constants for my thermistor. But I mostly care about dR/dT, and not accuracy.

George H.

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Steinhart-Hart can be accurate to about a thousandth of a degree Celcius.

YSI sells interchangable thermistors which are accurate to 0.2C or better ( depending how much money you spend) but a single point calibration in a wel l stirred ice bath (0.000 Celcius to about 0.001 degrees Celcius) can get y ou there with those thermistors over quite a range of temperatures.

Bill Sloman, Sydney

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