HP Forum Archive 19

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The lost formula Message #1 Posted by designnut on 16 Jan 2011, 11:49 a.m. I thought the knowledge that this ccould be done migtht inspire someone to find it again. The formula for the resisttance of negative temperature coeffient thermistors. is agonizingly ccomplex and works in a limited range. When I bought my HP65 I was working with thermistors and tried to match the resistance temperature curve by trying various things. I used only 3 constants for the particular one I was trying to match. The part I recall is adding a large number (~1200) to the temperature in C and taking ln. I used one constant to fit the resistance of that particular size device. It was dirt simple and truly accurate over the full range. I looked in my books for marginal references to what I had done and found none. I thought the knowledge that itt had been done might stimulate others to find it. sam

Re: The lost formula Message #2 Posted by Garth Wilson on 16 Jan 2011, 3:00 p.m., in response to message #1 by designnut I'm sure it's on the manufacturers' websites.

Re: The lost formula Message #3 Posted by Dan W on 16 Jan 2011, 6:50 p.m., in response to message #1 by designnut Are you talking about the Steinhart-Hart equation?

Re: The lost formula Message #4 Posted by John B. Smitherman on 16 Jan 2011, 7:10 p.m., in response to message #3 by Dan W A bit of wikipedia: Thermistors Regards, John

Re: The lost formula Message #5 Posted by designnut on 17 Jan 2011, 12:20 a.m., in response to message #4 by John B. Smitherman On reading something everyone impress it on the matrix of "what they know". There can be nothing new under the sun, everything that can be learned has always been learned. You miss a lot of information that way. The impact of what I wrote is that there is a simple accurate method not disclosed by usual methods. Read the message with an open mind, your brains won't fall out. Sam

Re: The lost formula Message #6 Posted by Walter B on 17 Jan 2011, 2:05 a.m., in response to message #5 by designnut Sam, things which have been (very) tedious in the past may be far easier nowadays and become even easier in the future, caused by new insight or just compilations of older insights. This process goes on and on. As a famous scientist once said: "We are standing on the shoulders of giants." HTH, Walter Edited: 17 Jan 2011, 2:09 a.m.

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