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LMT70A: Engineers may find the following 4 quartic piecewise-polynomial for converting voltage to temperature

Part Number: LMT70A
Other Parts Discussed in Thread: LMT70, TMP117

The LMT70A  seems a very useful device, I am evaluating it as an IceCell 0C reference point replacement for themocouples.

Using the values in : 8.6 Electrical Characteristics Temperature Lookup Table (LUT)

engineers may find the following 4 quartic piecewise-polynomial for converting voltage to temperature :

It consists of 4 quartic polynomials (5 values each), constrained to be continuous in value and gradient at each breakpoint.
The last 2 columns are the breakpoints (voltages) for which each quartic is valid.

125.2532032081 -25.093326337 -0.2163930501 0.0980485104 -0.0323894142 302.785 574.06875
70.19241188 -29.9908860459 -0.17680832 -0.0080389126 -0.0053856012 574.06875 891.11625
15.1587296697 -24.9915729533 -0.1455544095 -0.007279563 -0.0007347763 891.11625 1149.00275
-32.3274977901 -22.4931203736 -0.1640761645 -0.0136061522 -0.0015646034 1149.00275 1375.219

At the quoted table temperature values the following graph shows the output temperature errors as a function of temperature :

So it seems to be better than 1 mK up to 100C. 

Using the table voltage for 0C of 1097.987, we get :

1097.987000      0.000079

Hope that this helps,

Dr. Beau Webber




 

  • Hi Beau,

    Thanks for your interest in LMT70. We are proud of the performance achieved with LMT70. TMP117 is another great high accuracy temperature sensor from TI. I could send you an EVM if you're interested in checking it out!

    ren

  • Ren Schackmann said:

    Hi Beau,

    Thanks for your interest in LMT70. We are proud of the performance achieved with LMT70. TMP117 is another great high accuracy temperature sensor from TI. I could send you an EVM if you're interested in checking it out!

    ren

    Yes very much indeed, I would love an EVM - I did not know that they existed ....
    I have been contemplating trying to lay-out a tiny PCB, and have them etched and assembled, but one could fit 100s or 1000s on the smallest PCB I can get etched !!
    I have a spare channel on the 5 channel 24 bit USB interfaced DVM  I have designed for my thernocouples.

    Can you access my email address / postal address ?
    cheers,

    Beau

  • Oh I see the EVM comes with its own micro-controller and USB port - fantastic,  life just got easier !

    cheers, Beau

  • Hi Beau,

    I'll follow up with you in a private message.

    thanks,

    ren