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a mysterious sensor

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  a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-04-30 18:19 +0000
    Re: a mysterious sensor tabbypurr@gmail.com - 2017-04-30 12:08 -0700
    Re: a mysterious sensor Hul Tytus <ht@panix.com> - 2017-04-30 21:49 +0000
    a mysterious sensor pcdhobbs@gmail.com - 2017-04-30 15:04 -0700
      Re: a mysterious sensor Cursitor Doom <curd@notformail.com> - 2017-04-30 23:02 +0000
        Re: a mysterious sensor BM2335 <BM265@DMM.com.au> - 2017-05-01 11:19 +0800
      Re: a mysterious sensor Don Kuenz <g@crcomp.net> - 2017-05-01 03:06 +0000
        Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:17 +0000
      Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:16 +0000
    a mysterious sensor Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-04-30 15:46 -0700
      Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:20 +0000
    Re: a mysterious sensor Jon Elson <elson@pico-systems.com> - 2017-04-30 21:27 -0500
      Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:21 +0000
        Re: a mysterious sensor Jon Elson <jmelson@wustl.edu> - 2017-05-01 14:13 -0500
          Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 19:42 +0000
    Re: a mysterious sensor Frank Miles <fpm@u.washington.edu> - 2017-05-01 02:53 +0000
      Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:24 +0000
    Re: a mysterious sensor George Herold <gherold@teachspin.com> - 2017-05-01 05:11 -0700
      Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 14:21 +0000
    Re: a mysterious sensor "nuny@bid.nes" <alien8752@gmail.com> - 2017-05-01 13:17 -0700
      Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-02 07:46 +0000

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#458123 — a mysterious sensor

Hi,
been doing some sensor stuff.
I connect those to a PIC micro and an POE ethernet module, and send UDP data that way.

Today was the turn for the relative humidity and temperature sensor DHP11.

It is supposed to be within a few percent accuracy for RH.

However with 60 % RH it displays 20 %....
I have 2 and both do the same, software is good and checksum of communication is good.

So started googling, seems MANY people have the same problem,
nobody solved it, some people just wrote some correction math...
That is what I am doing now too (and ordered an other sensor type).

But, playing with it, trying to find out what I did wrong or what was wrong with those sensors:

I noticed that if I put my finger on it the reading went way up from 20 % to over 60 %.

Heat? no, also if I put my finger 5 mm away next to it...
Tried a light bulb (Edison type), hot, no effect on RH.
Tried a hot piece of metal: no effect on RH.
Tried a dark screen, tried a high brightness CREE flashlight: no effect.
Tried radiation sources (uranium marbles, thorium rods): no effect.

Tried a wet piece of cloth next to it, way up it goes.
But but, my fingers are DRY.

So dry I need to wet those to open a sandwich bag...

So WTF is going on ?
Interesting physics, it seems to sense blood THROUGH the skin at a distance?? (theory 1).

But HOW come these sensors are wrong for so many people ?
It says in the data sheet that there is an internal lookup table in the on board micro it has for calibration (not use accessible AFAIK).

Now I remember a discussion here years ago about customs using Xrays to check things, erasing chips,
could have happened and would explain why so many people have this problem (theory 2),
especially as datasheet mentions:
 5) Light Affect
        long time exposure to strong sunlight and ultraviolet may debase DHT's performance.
 UV, Xray?

But a sensor that can detect blood through the skin?
Or has our body a moisture halo around it all the time?

Anybody here played with the DHT11?

Any application for this effect?

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#458131

On Sunday, 30 April 2017 19:19:10 UTC+1, Jan Panteltje  wrote:
> Hi,
> been doing some sensor stuff.
> I connect those to a PIC micro and an POE ethernet module, and send UDP data that way.
> 
> Today was the turn for the relative humidity and temperature sensor DHP11.
> 
> It is supposed to be within a few percent accuracy for RH.
> 
> However with 60 % RH it displays 20 %....
> I have 2 and both do the same, software is good and checksum of communication is good.
> 
> So started googling, seems MANY people have the same problem,
> nobody solved it, some people just wrote some correction math...
> That is what I am doing now too (and ordered an other sensor type).
> 
> But, playing with it, trying to find out what I did wrong or what was wrong with those sensors:
> 
> I noticed that if I put my finger on it the reading went way up from 20 % to over 60 %.
> 
> Heat? no, also if I put my finger 5 mm away next to it...
> Tried a light bulb (Edison type), hot, no effect on RH.
> Tried a hot piece of metal: no effect on RH.
> Tried a dark screen, tried a high brightness CREE flashlight: no effect.
> Tried radiation sources (uranium marbles, thorium rods): no effect.
> 
> Tried a wet piece of cloth next to it, way up it goes.
> But but, my fingers are DRY.
> 
> So dry I need to wet those to open a sandwich bag...
> 
> So WTF is going on ?
> Interesting physics, it seems to sense blood THROUGH the skin at a distance?? (theory 1).
> 
> But HOW come these sensors are wrong for so many people ?
> It says in the data sheet that there is an internal lookup table in the on board micro it has for calibration (not use accessible AFAIK).
> 
> Now I remember a discussion here years ago about customs using Xrays to check things, erasing chips,
> could have happened and would explain why so many people have this problem (theory 2),
> especially as datasheet mentions:
>  5) Light Affect
>         long time exposure to strong sunlight and ultraviolet may debase DHT's performance.
>  UV, Xray?
> 
> But a sensor that can detect blood through the skin?
> Or has our body a moisture halo around it all the time?
> 
> Anybody here played with the DHT11?
> 
> Any application for this effect?

fingers are far from dry.


NT

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#458157

Jan   you might check the data sheet for response time. Most of the ones 
I've seen are very slow.

Hul

Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote:
> Hi,
> been doing some sensor stuff.
> I connect those to a PIC micro and an POE ethernet module, and send UDP data that way.

> Today was the turn for the relative humidity and temperature sensor DHP11.

> It is supposed to be within a few percent accuracy for RH.

> However with 60 % RH it displays 20 %....
> I have 2 and both do the same, software is good and checksum of communication is good.

> So started googling, seems MANY people have the same problem,
> nobody solved it, some people just wrote some correction math...
> That is what I am doing now too (and ordered an other sensor type).

> But, playing with it, trying to find out what I did wrong or what was wrong with those sensors:

> I noticed that if I put my finger on it the reading went way up from 20 % to over 60 %.

> Heat? no, also if I put my finger 5 mm away next to it...
> Tried a light bulb (Edison type), hot, no effect on RH.
> Tried a hot piece of metal: no effect on RH.
> Tried a dark screen, tried a high brightness CREE flashlight: no effect.
> Tried radiation sources (uranium marbles, thorium rods): no effect.

> Tried a wet piece of cloth next to it, way up it goes.
> But but, my fingers are DRY.

> So dry I need to wet those to open a sandwich bag...

> So WTF is going on ?
> Interesting physics, it seems to sense blood THROUGH the skin at a distance?? (theory 1).

> But HOW come these sensors are wrong for so many people ?
> It says in the data sheet that there is an internal lookup table in the on board micro it has for calibration (not use accessible AFAIK).

> Now I remember a discussion here years ago about customs using Xrays to check things, erasing chips,
> could have happened and would explain why so many people have this problem (theory 2),
> especially as datasheet mentions:
>  5) Light Affect
>         long time exposure to strong sunlight and ultraviolet may debase DHT's performance.
>  UV, Xray?

> But a sensor that can detect blood through the skin?
> Or has our body a moisture halo around it all the time?

> Anybody here played with the DHT11?

> Any application for this effect?

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#458160

Welcome back, Jan. We've missed you. 

Skin has liquid water on one side and relatively dry air on the other. The concentration gradient drives a lot of water vapour flow from the skin to the air. 

Cheers

Phil Hobbs

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#458173

On Sun, 30 Apr 2017 15:04:11 -0700, pcdhobbs wrote:

> Welcome back, Jan. We've missed you.

+1

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#458190

On 01-May-17 7:02 AM, Cursitor Doom wrote:
> On Sun, 30 Apr 2017 15:04:11 -0700, pcdhobbs wrote:
> 
>> Welcome back, Jan. We've missed you.
> 
> +1
> 
+2

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#458189

pcdhobbs@gmail.com wrote:
> Welcome back, Jan. We've missed you.

+1

Thank you,

--
Don Kuenz KB7RPU

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#458203

On a sunny day (Mon, 1 May 2017 03:06:28 -0000 (UTC)) it happened Don Kuenz
<g@crcomp.net> wrote in <20170430c@crcomp.net>:

>
>pcdhobbs@gmail.com wrote:
>> Welcome back, Jan. We've missed you.
>
>+1
>
>Thank you,

Thank (or blame) Bil Sloman, he emailed me a while back and reminded me of SED.

 

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#458202

On a sunny day (Sun, 30 Apr 2017 15:04:11 -0700 (PDT)) it happened
pcdhobbs@gmail.com wrote in
<93c89c28-9b1f-455d-949d-588130f5a951@googlegroups.com>:

>Welcome back, Jan. We've missed you. 
>
>Skin has liquid water on one side and relatively dry air on the other. The concentration gradient drives a lot of water vapour
>flow from the skin to the air. 
>
>Cheers
>
>Phil Hobbs

Thank you.
Yes, could be 'sweat fog' to keep body temperature constant.

It triggered memories of Kirlian photography:
 https://en.wikipedia.org/wiki/Kirlian_photography
 look at the picture of the finger tip.
  Sure moisture would do something in HV environment. 
   <myth destroyed? ;-) >

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#458171

I seem to rember those sensor needing to be reconditioned if they have been stored wrong. Some like a 2 hour bake at 100c 

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#458204

On a sunny day (Sun, 30 Apr 2017 15:46:44 -0700 (PDT)) it happened Lasse
Langwadt Christensen <langwadt@fonz.dk> wrote in
<977767d7-23a5-49b7-b20c-0e2fd9a5e7d4@googlegroups.com>:

>I seem to rember those sensor needing to be reconditioned if they have been stored wrong. Some like a 2 hour bake at 100c 

Well datasheet says 

(1) Operating conditions
Applying the DHT11 sensor beyond its working range stated in this datasheet can result in 3%RH
signal shift/discrepancy. The DHT11 sensor can recover to the calibrated status gradually when
it gets back to the normal operating condition and works within its range. Please refer to (3) of
this section to accelerate its recovery. Please be aware that operating the DHT11 sensor in the
non-normal working conditions will accelerate sensor's aging process.

(2) Attention to chemical materials
Vapor from chemical materials may interfere with DHT's sensitive-elements and debase its
sensitivity. A high degree of chemical contamination can permanently damage the sensor.

(3) Restoration process when (1) & (2) happen
Step one: Keep the DHT sensor at the condition of Temperature 50~60Celsius, humidity <10%RH
for 2 hours;
Step two:K keep the DHT sensor at the condition of Temperature 20~30Celsius, humidity
>70%RH for 5 hours.
(4) Temperature Affect

This refers to a 3% error...
Mine have a 300 % error (20 % versus 60 %)
Not sure baking would help.

I tried running it outside last night with my compensation math:
 http://panteltje.com/pub/humitidy_temp_outside.gif
seems usable, seems to match the local weather station (few miles away).

Need to fix the display algo for leading zero... (position).
red is temperature, blue is humidity, once every hour.

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#458184

Jan Panteltje wrote:

> Hi,
> been doing some sensor stuff.
> I connect those to a PIC micro and an POE ethernet module, and send UDP
> data that way.
> 
> Today was the turn for the relative humidity and temperature sensor DHP11.
> 
I've been using Phys_Chem Scinetific humidity sensors in my environmantal 
monitoring system for 20+ years.  They seem to work quite well, and although 
I have not rechecked the calibration, it seems to still be reasonable.
These are capacitive sensors, and need a circuit built out of an Analog 
Devices audio chip.

Jon

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#458205

On a sunny day (Sun, 30 Apr 2017 21:27:53 -0500) it happened Jon Elson
<elson@pico-systems.com> wrote in
<H5idnVTVQpa1AJvEnZ2dnUU7-dWdnZ2d@giganews.com>:

>Jan Panteltje wrote:
>
>> Hi,
>> been doing some sensor stuff.
>> I connect those to a PIC micro and an POE ethernet module, and send UDP
>> data that way.
>> 
>> Today was the turn for the relative humidity and temperature sensor DHP11.
>> 
>I've been using Phys_Chem Scinetific humidity sensors in my environmantal 
>monitoring system for 20+ years.  They seem to work quite well, and although 
>I have not rechecked the calibration, it seems to still be reasonable.
>These are capacitive sensors, and need a circuit built out of an Analog 
>Devices audio chip.
>
>Jon

Interesting, frequency change based? Or leakage based?

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#458257

Jan Panteltje wrote:

> On a sunny day (Sun, 30 Apr 2017 21:27:53 -0500) it happened Jon Elson
> <elson@pico-systems.com> wrote in
> <H5idnVTVQpa1AJvEnZ2dnUU7-dWdnZ2d@giganews.com>:
> 
>>Jan Panteltje wrote:
>>
>>> Hi,
>>> been doing some sensor stuff.
>>> I connect those to a PIC micro and an POE ethernet module, and send UDP
>>> data that way.
>>> 
>>> Today was the turn for the relative humidity and temperature sensor
>>> DHP11.
>>> 
>>I've been using Phys_Chem Scinetific humidity sensors in my environmantal
>>monitoring system for 20+ years.  They seem to work quite well, and
>>although I have not rechecked the calibration, it seems to still be
>>reasonable. These are capacitive sensors, and need a circuit built out of
>>an Analog Devices audio chip.
>>
>>Jon
> 
> Interesting, frequency change based? Or leakage based?
Oh, boy, this requires deep digging in the old memory banks.  I THINK it 
uses constant frequency, and measures the capacitance by how much AC is 
coupled to a resistive load.  I THINK that's how it works.  I built these 
from an app note almost 30 years ago, and they've just been perking along 
since.  I think these sensors are the same type as used in a number of VCRs 
to shut them down if close to dew conditions.

Jon

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#458260

On a sunny day (Mon, 01 May 2017 14:13:49 -0500) it happened Jon Elson
<jmelson@wustl.edu> wrote in <guOdnf4xx4zzFZrEnZ2dnUU7-YOdnZ2d@giganews.com>:

>Jan Panteltje wrote:
>
>> On a sunny day (Sun, 30 Apr 2017 21:27:53 -0500) it happened Jon Elson
>> <elson@pico-systems.com> wrote in
>> <H5idnVTVQpa1AJvEnZ2dnUU7-dWdnZ2d@giganews.com>:
>> 
>>>Jan Panteltje wrote:
>>>
>>>> Hi,
>>>> been doing some sensor stuff.
>>>> I connect those to a PIC micro and an POE ethernet module, and send UDP
>>>> data that way.
>>>> 
>>>> Today was the turn for the relative humidity and temperature sensor
>>>> DHP11.
>>>> 
>>>I've been using Phys_Chem Scinetific humidity sensors in my environmantal
>>>monitoring system for 20+ years.  They seem to work quite well, and
>>>although I have not rechecked the calibration, it seems to still be
>>>reasonable. These are capacitive sensors, and need a circuit built out of
>>>an Analog Devices audio chip.
>>>
>>>Jon
>> 
>> Interesting, frequency change based? Or leakage based?
>Oh, boy, this requires deep digging in the old memory banks.  I THINK it 
>uses constant frequency, and measures the capacitance by how much AC is 
>coupled to a resistive load.  I THINK that's how it works.  I built these 
>from an app note almost 30 years ago, and they've just been perking along 
>since. 

OK, datasheet of the new sensors I ordered (google AM2302.pdf many links) says it is capacitive too.
This DHT11 I am having problems with, says it uses a resistive type.
The fact that yours works so well for so long gives me hope the new sensors will be OK.
The DHT11 that gave 20 % RH now gives 48 % RH while it is 60 % RH, fast aging, was outside all night and it rained :-)
Just wrote the PIC asm code for that AM2302, slightly different from the DHT11, so am ready when those arrive.


>I think these sensors are the same type as used in a number of VCRs 
>to shut them down if close to dew conditions.

Ha, Sony Umatic helical scan, I remember in Rome in a sports hall needed to record, and the d*mn thing would not.
used an electric heater blower to get it working just in time :-)
Now that was long ago too.

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#458188

On Sun, 30 Apr 2017 18:19:05 +0000, Jan Panteltje wrote:

> Hi,
> been doing some sensor stuff.
> I connect those to a PIC micro and an POE ethernet module, and send UDP
> data that way.

Welcome back!

Have you tried checking the calibration of the device?
One fairly straightforward/cheap way is to create a slurry of a salt and 
water.  The particular salt (in a small enclosed space) forces a 
particular humidity.  Do a web search and you'll find a few examples.

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#458206

On a sunny day (Mon, 1 May 2017 02:53:06 -0000 (UTC)) it happened Frank Miles
<fpm@u.washington.edu> wrote in <oe67ui$url$1@dont-email.me>:

>On Sun, 30 Apr 2017 18:19:05 +0000, Jan Panteltje wrote:
>
>> Hi,
>> been doing some sensor stuff.
>> I connect those to a PIC micro and an POE ethernet module, and send UDP
>> data that way.
>
>Welcome back!
>
>Have you tried checking the calibration of the device?
>One fairly straightforward/cheap way is to create a slurry of a salt and 
>water.  The particular salt (in a small enclosed space) forces a 
>particular humidity.  Do a web search and you'll find a few examples.

Yes, clearly the calibration is wrong
I did the wet salt test etc to calibrate my old 'analog' mechanical humidity sensor years ago,
that one is still OK.

Then the idea came to put a camera on that, and scan the image circular in ever bigger circles,
correlation of brightness changes in the circles then gives the position of the hands,...
It has 2 hands, one moves, and one you can set as reference,.
Difference in color can tell which one is which..
But the 2 $ sensor is faster, cheaper, smaller, and better,
But if it MUST be ;-)

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#458217

On Sunday, April 30, 2017 at 2:19:10 PM UTC-4, Jan Panteltje wrote:
> Hi,
> been doing some sensor stuff.
> I connect those to a PIC micro and an POE ethernet module, and send UDP data that way.
> 
> Today was the turn for the relative humidity and temperature sensor DHP11.
> 
> It is supposed to be within a few percent accuracy for RH.
> 
> However with 60 % RH it displays 20 %....
> I have 2 and both do the same, software is good and checksum of communication is good.
> 
> So started googling, seems MANY people have the same problem,
> nobody solved it, some people just wrote some correction math...
> That is what I am doing now too (and ordered an other sensor type).
> 
> But, playing with it, trying to find out what I did wrong or what was wrong with those sensors:
> 
> I noticed that if I put my finger on it the reading went way up from 20 % to over 60 %.
> 
> Heat? no, also if I put my finger 5 mm away next to it...
> Tried a light bulb (Edison type), hot, no effect on RH.
> Tried a hot piece of metal: no effect on RH.
> Tried a dark screen, tried a high brightness CREE flashlight: no effect.
> Tried radiation sources (uranium marbles, thorium rods): no effect.
> 
> Tried a wet piece of cloth next to it, way up it goes.
> But but, my fingers are DRY.
> 
> So dry I need to wet those to open a sandwich bag...
> 
> So WTF is going on ?
> Interesting physics, it seems to sense blood THROUGH the skin at a distance?? (theory 1).
> 
> But HOW come these sensors are wrong for so many people ?
> It says in the data sheet that there is an internal lookup table in the on board micro it has for calibration (not use accessible AFAIK).
> 
> Now I remember a discussion here years ago about customs using Xrays to check things, erasing chips,
> could have happened and would explain why so many people have this problem (theory 2),
> especially as datasheet mentions:
>  5) Light Affect
>         long time exposure to strong sunlight and ultraviolet may debase DHT's performance.
>  UV, Xray?
> 
> But a sensor that can detect blood through the skin?
> Or has our body a moisture halo around it all the time?
> 
> Anybody here played with the DHT11?
> 
> Any application for this effect?

Jan! 
I never measured RH, but it should be a strong function of temperature.
(I think temperature is the "relative" part in relative humidity.) 

Find a different sensor? 
George H. 

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#458228

On a sunny day (Mon, 1 May 2017 05:11:37 -0700 (PDT)) it happened George
Herold <gherold@teachspin.com> wrote in
<4057b28b-5cb6-42c0-bb6e-3915f87a8037@googlegroups.com>:

>Jan! 
>I never measured RH, but it should be a strong function of temperature.
>(I think temperature is the "relative" part in relative humidity.) 

Indeed, that is why the temp sensor is in the same unit, and its
micro does the correction, or at least it should.


>Find a different sensor? 

This is the DHT11, I now ordered 2 AM2302, supposed to be equal to the DHT22.

AM2302 has a RH range of 0-99.9% in steps of .1 %
DHT11 of 20-90% in steps of 1%.
Software and hardware interface seem the same, no need for new code AFAIK.
Both are 'factory calibrated'.
Of course that does not work if customs xrays those and erases the on board micro's calibration constants (my guess what happened).

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#458266

On Sunday, April 30, 2017 at 11:19:10 AM UTC-7, Jan Panteltje wrote:
> Hi,
> been doing some sensor stuff.
> I connect those to a PIC micro and an POE ethernet module, and send UDP data
> that way.
> 
> Today was the turn for the relative humidity and temperature sensor DHP11.
> 
> It is supposed to be within a few percent accuracy for RH.
> 
> However with 60 % RH it displays 20 %....
> I have 2 and both do the same, software is good and checksum of communication
> is good.
> 
> So started googling, seems MANY people have the same problem,
> nobody solved it, some people just wrote some correction math...
> That is what I am doing now too (and ordered an other sensor type).
> 
> But, playing with it, trying to find out what I did wrong or what was wrong
> with those sensors:
> 
> I noticed that if I put my finger on it the reading went way up from 20 % to
> over 60 %.
> 
> Heat? no, also if I put my finger 5 mm away next to it...
> Tried a light bulb (Edison type), hot, no effect on RH.
> Tried a hot piece of metal: no effect on RH.
> Tried a dark screen, tried a high brightness CREE flashlight: no effect.
> Tried radiation sources (uranium marbles, thorium rods): no effect.
> 
> Tried a wet piece of cloth next to it, way up it goes.
> But but, my fingers are DRY.
> 
> So dry I need to wet those to open a sandwich bag...
> 
> So WTF is going on ?

  Seems electrostatic to me.


  Mark L. Fergerson

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