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#1 27-08-2013 23:00:14

brianmca
Member
Registered: 29-08-2012
Posts: 9

T3511 humidity sensor problem

We have a T3511 with an external probe, about 1 year old.  The humidity sensor appears to falsely jump to 100% and get stuck there.  Here's an example (blue line is temp, green is dewpoint):
http://blast02.mit.edu/tmp/ext_comet-day.png
Here's what another (non-Comet) sensor showed for the same time:
http://blast02.mit.edu/tmp/ext_tempf-day.png
Is the probe damaged ? Defective ?  It did not behave like this when we got it.
Note: the deviation in the temperature at 18:00 is due to an inadequate sun shield, as is the bump at 07:00 on the other sensor.

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#2 28-08-2013 07:19:01

HonzaD
Administrator
Registered: 11-08-2008
Posts: 293

Re: T3511 humidity sensor problem

Hi brianmca,

You wrote too few information and I am not able say what can be wrong.

But let me guess ... your dew point is very close to condensation. And I think condensation is your problem. When condensation occurs watter vapour from air change state to liquid. And if there is liquid under sensor cover, device shows 100%RH. If you were carefully remove sensor cover in this state you find under sensor cover liquid water. IMPORTANT! If you decide to remove sensor cover, do not touch the sensors. Any touch can damage them.



Jan

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#3 28-08-2013 21:59:36

brianmca
Member
Registered: 29-08-2012
Posts: 9

Re: T3511 humidity sensor problem

HonzaD wrote:

You wrote too few information and I am not able say what can be wrong.

This is what I have.  If you can suggest something specific to look at, please do.

HonzaD wrote:

But let me guess ... your dew point is very close to condensation. And I think condensation is your problem. When condensation occurs watter vapour from air change state to liquid. And if there is liquid under sensor cover, device shows 100%RH. If you were carefully remove sensor cover in this state you find under sensor cover liquid water. IMPORTANT! If you decide to remove sensor cover, do not touch the sensors. Any touch can damage them.

Jan

That something I've considered but can't easily investigate.  However, it wasn't doing this when we installed it.  Here's a typical day from September 2012:

http://blast02.mit.edu/tmp/ext_comet-day0912.png

Why would we be having condensation issues now ?

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#4 29-08-2013 07:13:58

PetrS
Administrator
Registered: 29-05-2007
Posts: 34

Re: T3511 humidity sensor problem

There is necessary to provide more information about place of instalation and application (where and how the equipment is used). Place instalation photo welcomed. From your graph it seems to be condensation during night (from 2 AM till morning).

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