Interpreting Thermistor Tables
Interpreting Thermistor Tables
(OP)
I am trying to substitute a thermistor which gives me resistance values in steps of 10 Ohms from zero to 100.
0=9750. 10=5970, 20=3747 - - - - - -100=204 Ohms
When I look at the thermocouple parts lists they rate the devices in a totally different fashion Rt/R25 (related to 25°C and use some very complicated formulae to describe the slope
Typical 0°C = 2.813 Rt/25C 100°C = 0.95690 Rt/25C
How do I convert these values into Ohms so that I can compare Apples to Apples?
Thanks
Roy
0=9750. 10=5970, 20=3747 - - - - - -100=204 Ohms
When I look at the thermocouple parts lists they rate the devices in a totally different fashion Rt/R25 (related to 25°C and use some very complicated formulae to describe the slope
Typical 0°C = 2.813 Rt/25C 100°C = 0.95690 Rt/25C
How do I convert these values into Ohms so that I can compare Apples to Apples?
Thanks
Roy





RE: Interpreting Thermistor Tables
Or is it RTDs you want to use? Doesn't work either. If you do not change the electronic system as well.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Interpreting Thermistor Tables
I am trying to source a replacement for an existing Thermistor but having trouble.
Nearly every document I find refers to a complex Steinhart-Hart thermistor equation and the tables don't say what the resistance is at any given temperature just refer to the Rt at 25°C
I'm no math whiz but how do you know what Rt is in Ohms from that?
I gather different materials have different slopes, no I don't know what mine is made of
Other lists give the resistance at 25°C and a ratio
I don't need an exact match but I would like to get close at least.
RE: Interpreting Thermistor Tables
http://www.veris.com/docs/support/faq/RTD-Thermist...
the table is quite enlightening, as it lists the thermistor value changes for a 10k Rt with different materials. If you're only operating in the positive temperature ranges, then you might get something like a 5°C error if you have the right Rt, but the wrong material.
TTFN
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RE: Interpreting Thermistor Tables
Check out the thermistor entry on wikipedia. In particular, look at the B or Beta parameter equation:
R=R0eB(1/T-1/T0)
Note that R0 in that equation is the resistance at T0. Temp must be in Kelvin. Basically any R and T that match will do. So you can use R25 for R0 in that equation, and 298.15 for T0.
So to recap, R0 is R at 25C. T0 is 25C, converted to Kelvin. B comes from the datasheet for the resistor. If you can find R0 and B for your current thermistor, you should be able to find a cross easily. If not, you should use the equation to generate a table for some possible crosses, and compare the table to your existing part.
In principle, you could even enter the values from your table and solve for B, which would also make it easy to find a cross.
Good luck!
RE: Interpreting Thermistor Tables
After looking for days I just happened on the exact match from Vechay 3000 Ohms at 25°C
The table I found listed the Ohms in 10° increments, I'm not sure why the other vendors list in such a complicated manner
Thanks for your help
RE: Interpreting Thermistor Tables
TTFN
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RE: Interpreting Thermistor Tables
I can't figure out why they make it so difficult unless it's to cover every different 25 C value for a particular material
Vechay had a table showing resistance for each 10 degrees of C.
RE: Interpreting Thermistor Tables
At a minimum most tables would require an offset calibration.
TTFN
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