MPL3115A2 warm-up drifting:

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MPL3115A2 warm-up drifting:

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associationadra
Contributor I

Hi all,

I'm using a MPL3115A2 in an altimeter application; during the 3 to 4 first minutes, the measured altitude decreases of about 40 to 50 ft. Then it becomes more stable. The unit is placed on a table, in a lightproof box. The only light may come from a LED on the same PCB located about 6 cm. The measurement loop is:

if (interrupt){   // interrupt from MPL3115

   read (REG_OUT);   // read result

   read(REG_CTRL1) while(OST_bit == 1);   // read register to make sure OST = 0

  write(REG_CTRL1, 0xBA);   // set OSR = 128, OST=1, mode stand-by

}

My questions are:

1/ has anyone noticed a kind of warm-up period for this device making its accuracy being poor for a while  or is this phenomena specific for mine, meaning a failure of this very device ? (I have not tested any other specimen as I have only one...)

2/ In cas this issue is known, is there any hardware or software workaround ?

3/ is my measurement procedure correct ?

Thanks a lot in advance,

Gerard

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588 Views
associationadra
Contributor I

Thank you Jose for your answer.

I leave a tempo of 6 seconds before the first measurement; the problem occurs the same way, weither the PCB would be inside the box or outside with a litle piece of clothe protecting it from the direct  light. Anyway, the  back side of the box has holes allowing a natural air flow.

The problem happens after the unit has been switched off for a couple of hours. If I switch it off then on in less than a minute time, the problem does not occurs. This is why it makes me think of a "warm-up" time. The loss of read altitude decreases (never increases) during 3 to 4 minutes in a range of 30 to 40 feet before being stable.

Please also notice that the offset I have to set in the OFF-P register is 9 to have the correct altitude with the QNH given by airport when the device is stable.

When you say that it is not normal, should I understand that I should try with another sample ?

Thanks,

Regards

Gerard

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588 Views
reyes
NXP TechSupport
NXP TechSupport

Hi Gerard,

 

Yes, I don’t think that this is normal behavior for the MPL3115A2. This device can be easily damaged when soldering to the PCB, it could be damaged during soldering, I do recommend you to test with another sample.


Have a great day,
Jose

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588 Views
associationadra
Contributor I

Ok, thanks Jose, I'll order à new one, and I'll let you know.

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588 Views
reyes
NXP TechSupport
NXP TechSupport

Hi Gerard,

 

3 to 4 minutes of warm-up time is not normal, altimeter signal should be stable a few seconds after turning on the device.

 

Direct exposure of light to the hole at the top of the sensor does affect the reading of the sensors, but for test purposes please make measurements of the altimeter placed outside of the box, I’m thinking that the sealed box is affecting the altitude readings of the sensor.


Have a great day,
Jose

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588 Views
associationadra
Contributor I

Thank you Jose for your answer.

I leave a tempo of 6 seconds before the first measurement; the problem

occurs the same way, weither the PCB would be inside the box or outside

with a litle piece of clothe protecting it from the direct light.

Anyway, the back side of the box has holes allowing a natural air flow.

The problem happens after the unit has been switched off for a couple of

hours. If I switch it off then on in less than a minute time, the

problem does not occurs. This is why it makes me think of a "warm-up"

time. The loss of read altitude decreases (never increases) during 3 to

4 minutes in a range of 30 to 40 feet before being stable.

Please also notice that the offset I have to set in the OFF-P register

is 9 to have the correct altitude with the QNH given by airport when the

device is stable.

When you say that it is not normal, should I understand that I should

try with another sample ?

Thanks,

Regards

Gerard

Le 10/10/2017 à 19:34, reyes a écrit :

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Re: MPL3115A2 warm-up drifting:

reply from Jose Alberto Reyes Morales

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