Why are my HTS221s getting bad Humidity values?

[M.Mardini]

Hello,

My company is using since more than one year a combination from HTS221 and stm32f407 uController , I2C is used.

The problem is that on some devices i have from the sensor different results.

also some sensors give correct output where the others give lower values, where both of them have the same circumstanses. like the same board design and the same uController firmware.

in the attachment there are the output data from two sensors.

I wonder where the problem could be?

We use the follwing adjustment :

PD = 1: active mode

1Hz

other CTRL-REG are disabled,

we have activatet the heat register for 4 seconds,but that did not solve the problem.

we are very thankful for any help :grinning_face:

[M.Mardini]

Update, the assmbler company told me that they did not do any re-hydration. what can i do in this situation ?

we are very thankful for any help :grinning_face:

[Eleon BORLINI]

Hi @M.Mardini​ ,

if also the heater doesn't sort any effect (this would have been the first thing I would have suggested you) you could try with a bake procedure at 85° (and 85RH), that should help to remove residual condensation on Sensor1, that seems to have prevented the measurement of the correct humidity.

The temperature you are measuring is ok?

Hope it is not damaged from a contaminating assembly...

-Eleon

[M.Mardini]

Hi @Eleon BORLINI​ , thank you very much for your Answer

we have baked the sensor with 70RH at (35°) for 12 hours (Data sheet). and today with 85RH for 1 hour, but that did not have any effect.

The Temperature measurement is Ok.

[Eleon BORLINI]

Hi @M.Mardini​ ,

which is the failure rate on your sensors? I mean, the number of devices not behaving well

And do the wrong data affect devices since the beginning, or do they fail after some time?

I'm by the way afraid it could be an issue related to the soldering process...

-Eleon

[M.Mardini]

HI @Eleon BORLINI​ , we have 10% failure rate in our sensors, and they failed since the beginning, we are now trying to know if we can solve this problem by adding our own Offset to the firmware, in the attachment there is the output data from a "bad" sensor.

it is obvious that the sensor is working but with a false offset.

[Eleon BORLINI]

Uhm, it looks stuck, compared with the other curve, the blue one (is a reference or goof humidity?)

But does the "failing" devices output vary while changing the environmental humidity, even if at a different level with respect to the correct one?

-Eleon

[M.Mardini]

-Sorry I did not explain very well, this information are from bad sensor, the blue curve is the humidity, and the red is Temperatur,

We put the sensor in climate cabinet at 21°C, and a tried to increase the humidity, the sensor has reacted well but with lower result.

We are now trying to find out the difference and solve this problem with our own offset.

thank you

I wish you a nice weekend

[Eleon BORLINI]

uh ok, I didn't understood... ok, keep me please updated about your progression

Have a nice weekend you too!

-Eleon

[M.Mardini]

Hallo @Eleon BORLINI​ ,

we have just discovered that the sensors do not have the same difference so we can not solve this problem through a new offset.

in the attachment there are output from 2 sensors. the difference are obviously not the same .

is there anything we can do?