How long does it take to turn on the heater in MEMS HTS221?

[iAlien]

[Uwe Bonnes]

Probably the heater turns on immediate with the command, but thermal capacitance together with the heating power (100 mW @3.3V) will result in a slope. You can perhaps estimate with the data from the material datasheet.

[iAlien]

How long is it safe to turn it on? microseconds? milliseconds? seconds? Sorry for my google translator

[S.Ma]

I guess the heater is to heat the sensing element and flush the humidity out. Monitoring the humidity and temperature should be possible while heater is on.... Normally datasheet will give you the operating range in temperature and humidity, so the answer could be it.

[iAlien]

Monitoring the humidity and temperature should be possible while heater is on.... 

No.

The Heater bit is used to control an internal heating element, that can effectively be used to

speed up the sensor recovery time in case of condensation.

Humidity and temperature output should not be read during the heating cycle; valid data can

be read out once the heater has been turned off, after the completion of the heating cycle. (c) Datasheet.

Thought that ST would open the veil of secrecy.

I will try to turn it on periodically until the humidity readings stop dropping.

[Eleon BORLINI · Accepted solution]

Hi @iAlien​ ,

the Heater is intended to recover condensation, so it is an "environmental" process that should last at least some seconds.

Typically, lab tests leave the heater on for 60s, but this helps recovering the full HTS221 operativity in 1/8 of the time than in the "No-Heater case"

Here some experimental data:

If my reply answered your question, please click on Select as Best at the bottom of this post. This will help other users with the same issue to find the answer faster.

-Eleon