Zetex ZNI1000 nickel RTD in a SOT-23 package. The third lead is the isolated substrate, the thermal contact.
Nickel resistance curves up with temperature, so it's linearized by loading.
+5------+ | 4K | | +----- V | | RTD | | gndgives +1 volt at 0 C, 1.440 at 100 C, pretty linear.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Within better than a tenth over 0-150°C (nominal RTD curve) so not much degradation of the 0.4°C+ tolerance, 4.206K is a bit better for linearity.
The < 1.5K source impedance is also okay to go directly into most microcontroller ADCs. A bit converter with 5V Vdd reference would yield 0.27°C resolution and ratiometric operation, fine for HVAC and such like.
I got the 4K by fiddling with a calculator; your number is no doubt better. I forget the platinum value, something like -2750 for a 100 ohm RTD.
This is part of my evolving (never-ending?) design of a realtime mosfet SOAR shutdown circuit, to push pulsed, linear-mode mosfets to the eve of destruction. This part can solder down right between the legs of a D2PAK.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
I numerically minimized the least squares error over the range. Weird equation for T(R).. I wonder how they came up with that.
Maybe too expensive, but have you considered a chipscale thermopile?
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
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