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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.

 125.253 -25.0933 -0.216393 0.0980485 -0.0323894 302.785 574.069 70.1924 -29.9909 -0.176808 -0.00803891 -0.0053856 574.069 891.116 15.1587 -24.9916 -0.145554 -0.00727956 -0.000734776 891.116 1149 -32.3275 -22.4931 -0.164076 -0.0136062 -0.0015646 1149 1375.22

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.

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