Range of -30 to 50 C is more than enough. I'm going to have a total of 6 probes but i can just mirror the circuitry for the rest. I found linear thermistors sold by omega and honeywell but they are expensive and from the schematics they only look like resistor networks. I found some circuits online which are nothing more than a voltage divider but i'm unable to verify there temperature accuracy. Or how well they linearize the curve. Also on some circuits i see that the solution calls for two thermistors along with a resistor network, any ideas what the benefits are to the second?
is one paper that describes linearization with one resistor. It is possible to make that combination even more linear (and less sensitive) with one additional resistor. I used to have an Excel sheet for that on my computer, but that seems to have been a few computers ago.
Resistors are temperature dependent, too and there are
thermistors with different -- even positive or negative --
temp. coeff. The networks you have found combine these
effects to improve the linearity.
On a single 6 thermistor temp. sensor you may reach .5C accuracy by calibration. The simplest would be using a microcomputer ( OP.AMP with noise filter, A/D converter and calibration table in the uC)
If you think for mass production, I would use some different e.g. resistive sensor . A welldesigned
diode-sensor may only have to be calibrated at two
points ( 0 and 100 C) to satisfy your need -- less
than 5 minutes per assembly.
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Please read FAQ240-1032
My WEB: <
Resolution and accuracy are two different matters. If you get a thermistor or PRT, you'll need something with about 0.1ºC accuracy just to do the calibration:
Thanks guys. I appreciate all your posts. I would like to use the micro except i'm using a PIC and i'm not that fluent in programming them (still learning) which is why i was looking for a hardware solution. I will probably just get the resistance tables from the manufacturer and try and program that into the controller. It seems to be the most accurate and most inexpensive method.
JKelly (and anyone):
I've found myself in the same situation of trying to find a simple hardware solution. Unfortunately I haven't found a solution yet.
I'm not trying to hi-jack your thread, nor do I want to start a new one since your issue is very similar. I figure an inquiry on how far along you have come might be more appropriate.
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