# tmp36 conversion formula or accuracy?

Question asked by tbarbe on Sep 7, 2014
Latest reply on Sep 19, 2014 by Lluis

Hi ( warning newbie! )

Im running thru the Arduino starter kit stuff and they include a TMP36 to do some temperature sensing on their starter projects...

I was able to get very accurate middle wire voltage readings from the Arduino ADC - that match the output of a multi-meter ( Brymen 869s ) - which I feel is pretty accurate for the voltage settings...

but for the formula's I am seeing everywhere... the temperature conversion from voltage does not come up with a number that makes sense... it seems a tad low... I have two other temperature sensors and they keep showing a 3-5 degree higher reading than the TMP36....but according to TMP36 spec - it should be within 1-2 degrees from accurate.... and since its showing 3-4 degrees out of wack compared to other temperature sensors - I feel like something in the math is wrong....

Is there anything I could do to improve the accuracy of the TMP36? is there some math I should do better with? or is it perhaps the sensor is actually 3-5 degrees off?

Ive been using different formulas from around the web - starting with the Arduino Project Book... and then trying AdaFruit formula here:

Im reading the Vcc voltage actually going into the circuit - and that improves it some.. but its still offset by enough to make me feel like someone is not proposing the proper math technique here.

I see this on the data sheet:

http://www.analog.com/static/imported-files/data_sheets/TMP35_36_37.pdf

the chart shows TMP36 running from .1v to 2.0 = 1.9v range ( 1900 mV )

it says 750mV = 25C

Im getting readings like 450mV to 700mV and its no where near that cold... what could be wrong?

Low voltage operation (2.7 V to 5.5 V) Calibrated directly in °C
10 mV/°C scale factor (20 mV/°C on
TMP37) ±2°C accuracy over temperature (typ)
±0.5°C linearity (typ)