how to understand the LIS3DH temperature reading

[satyajit2]

Posted on June 02, 2015 at 18:20

I have an application using the LIS3DH.  I need to read the values from the on chip Temperature Sensor.  I have properly setup the ADC_PD and TEMP_EN bit in the TEMP_CFG_REF (1Fh).  I'm reading the OUT_3_L (0Ch) and OUT_3_H (0Dh) at an ODR of 50 Hz.  The OUT_3_L seems to be random while OUT_3_H looks like valid data.  Three different chips measure (OUT_3_H)  as follows FA, F6 and FE.  This translates to -6, -9 and -2.  The Datasheet describes the TSDr as Temperature sensor output change vs temperature with a resolution of 1 digital/C.  So my assumption is that the translated values of -6, -9 and -2 are delta (changes) from some reference temperature (possible at MFG calibration).  The ambient temperature in the room is 23 C (~73 F).  My assumption per Datasheet was that the reference temperature is 25 C but this only correlated to the 3rd value.  Is there a reference temperature that is different in each chip? Is there a way to access this reference temperature? Possible in one of the reserved addresses?

Thank you,

#temperature-sensor #lis3dh

[satyajit2]

Posted on June 23, 2015 at 16:00

** BUMP **

Does anyone from ST look this forum? Anyone have information regarding my question?

[zsolt2]

Posted on April 01, 2016 at 15:02 Dear ketkar.satyaji, Have you managed to solve the problem? I have very a similar problem, but I always read out 0 from the OUT3_L/H registers. Chip seems to be configured properly, because other registers of the accelerometer (e.g. X, Y, Z parameters )gives good values. regards, Zsolt

[deval]

Posted on June 21, 2016 at 18:49

Hi ketkar,

I am using lis2dh. If you know then can you please tell me how to convert temperature raw data to actual temperature. I didn't find this info in datasheet.Is there any formula for this?Thanks..

[Miroslav BATEK]

Posted on July 11, 2016 at 09:14

The temperature sensor can be used to measure temperature variations. It isn't suitable to return absolute temperatures measures. 

The value represents difference respect to a reference not specified value.

Do following to correctly work with temperature sensor:

- enable the bits 6 and 7 in TEMP_CFG_REG(1Fh): enable aux ADC and enable temperature sensor.

- enable Block Data Update, BDU, feature. CTRL_REG4(0x23) , BDU (bit#7)=1.

- read both the ADC output 3 registers (because of BDU enabled): OUT_ADC_3_L(0x0C) and OUT_ADC_3_H(0x0D).

Data representation: 2's complement.

Useful bits: 8, left aligned, hence useful data in OUT_ADC_3_H.

Temperature sensor output change vs temperature: 1digit/degrCelsius

Best regards

Miroslav

[wittaya190]

Posted on November 09, 2016 at 16:22

Finally it starts to make sense to me.

I also use the LIS3DH and trying to understand the temperature reading from OUT_ADC3_H (0x0D). You may need a heat source to heat up the sensor to see the changes of the reading from OUT_ADC3_H. Here is the scenario:  -my initial reading from OUT_ADC3_H get a value 0xFA (translated to -6)  -consider this -6 value as a relative indicator of the temperature at the time of the reading.   assuming your ambient temperature was 24degree C.  -heat up the LIS3DH sensor with your choice of heat source.  -reading the OUT_ADC3_H again and you will see the new value goes up.  -each 1 degree C rise in the LIS3DH temperature will increment OUT_ADC3_H value by 1.  -ie, if a person apply a heat source and risen the LIS3DH temperature 10 degree C higher,   the OUT_ADC3_H will now give a new reading of 0x04 (-6+10=4). (The sensor is now 34 degree C)  -after cooling the sensor back down to the ambient temperature,   the OUT_ADC3_H will again give 0xFA (-6)    -According to ketkar.satyajit,  each chip may give different reading from the OUT_ADC3_H even from the same temperature.  Unfortunate, that's why the LIS3DH is not referenceing the reading to any fix reference.    Anyway, Happy Programmming.  Best regards,  Witt

[dehai wo]

Posted on October 26, 2017 at 09:00

when  LIS3DH is in room temperature condition(about 20°C), temperature variation data from the LIS3DH is as below:

temperature viriation is: -2,

temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2, temperature viriation is: -2,

if '

temperature variation' is the

Comparison results

 (current temperature to a base temperature)? if the value -2 represent the temperature variation compared to the last time , then -2-2-2....-2  equal to a very large value . then what is the base temperature? why the 

temperature variation of my sensor is so much while the ambient temperature is about constant?

[Miroslav BATEK]

Posted on October 26, 2017 at 10:01

The temperature sensor can be used to measure temperature variations. The output value represents difference respect to a reference not specified value.

So it is not variation compered to the last measurement. The base temperature is not known, you would have to do a calibration for each device.

Lats say the base temperature for your device is 25°C, so your measurement is 25 - 2 = 23°C 

[dehai wo]

Posted on October 26, 2017 at 10:10

Thanks a lot!!!

[dehai wo]

Posted on October 27, 2017 at 00:49

Then what is the purpose of the embedded temperature device ?