Harold wrote on Wed, 23 Jul 1997 11:48:47 EDT >On Tue, 22 Jul 1997 21:49:15 +0000 Gerald Lewis >writes: >>At 10:00 AM 7/22/97 GMT+0200, you wrote: > >> >>Whats wrong with a 25 cent thermistor and a series 1 % resistor to the >>+5 >>supply and possibly a shunt resistor to control range. The curve of >>the >>thermistor can be linearized by a small look up table in memory or by >>scaling according to the magnitude of the output of the 16C71 or >>equiv. >>on-board A/D converter. > > > Good point! I wonder how interchangable thermistors are. Can >you set up just one table and use it for production? Years and years ago >I discovered that the nonlinearity of therimistor resistance versus >temperature was just about the opposite of the nonlinearity of output >voltage of a voltage divider versus the resistance of the shunt resistor. > Thus, if you choose the pull-up resistor right, you can get a pretty >linear output directly out of the thermistor. It can, of course, always >be improved by a look-up table! > another interesting therimistor to use is an automotive water >temperature sensor. Pretty cheap and nice package fore measuring water >temperature in a pipe. > >Harold Hi, Any one considered the cheap (under $1.0) AD590 from Analog Devices? I use it regularly as it outputs resulsts directly in Deg Kelvin which covers a massive range, down to -273DegC. Deducting kelvin to centigrade is your answer of the measured temperature. A series resistor is all it needs and as it is a current based device distant mesurements are very easy. It also comes precaliberated in various ranges, though I must add that the maximum it can measure is about 150degC, enough for Mike's roof top measurements, unless ofcourse the roof is.....! -- CarryOn, Rajnish(NoEngineer) ************************************************ Rajnish Nischal Challenger's 18,DSIDC Sch - I, HVAC Instruments Okhla Ind - II, rajnischal@hotmail.com New Delhi, Tel : 91-011-6929396 India. 110020 Fax : 91-011-6942222 ************************************************* ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com