Repairing hygrometer transmitter

[hon...@yahoo.com]

I have one of those sort-of cheap Oregon Scientific weather stations with the wireless outdoor temperature/humidity sensors. It's maybe about 6 years old, so normally a person would simply buy a new one but I'm not like that. I like fixing stuff rather than tossing it.

The outdoor unit senses the temperature just fine, but not humidity. When it's not displaying 2% or 98% for RH, it's displaying another number that is more sane but still wrong. I took it apart and the sensor looks exactly like this:

http://www.shinyei.co.jp/stc/humidity_e/images/CL-M53R_L.jpg

Any pointers on how these work or what to look for? I've done nearly everything else but humidity. It appears these aren't driven with DC, which makes things more difficult. How probable is it that the sensor simply needs replacing?

[Tom Miller]

<hon...@yahoo.com> wrote in message
news:25ae0c4c-7e00-4215...@googlegroups.com...

+++++++++++++++++++++++++++

Try cleaning the sensor with isopropyl alcohol, 99% that you can get special
order from the pharmacy.

[Jim Thompson]

DENATURED Alcohol at most hardware stores.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

[hon...@yahoo.com]

On Friday, July 10, 2015 at 8:58:22 PM UTC-5, Tom Miller wrote:
> <h...m@yahoo.com> wrote in message

So is this not the same as standard rubbing alcohol? Incidentally I tried this, but no go.

[Tom Miller]

<hon...@yahoo.com> wrote in message
news:9b9a10ae-abd7-4c29...@googlegroups.com...

Standard rubbing alcohol is 30% water. You can get 91% alcohol OTS. Best for
sensitive electronics is 99+% but you will need to order it.

But this seems moot now.

[Jeff Liebermann]

On Sat, 11 Jul 2015 06:56:14 -0700 (PDT), hon...@yahoo.com wrote:

>On Friday, July 10, 2015 at 8:58:22 PM UTC-5, Tom Miller wrote:
>> <h...m@yahoo.com> wrote in message
>> news:25ae0c4c-7e00-4215...@googlegroups.com...
>> I have one of those sort-of cheap Oregon Scientific weather stations with
>> the wireless outdoor temperature/humidity sensors.

Does the wx station and sensor have model numbers?
Such information is amazingly useful and will tend to produce specific
answers instead generalized guesswork.

>> Try cleaning the sensor with isopropyl alcohol, 99% that you can get special
>> order from the pharmacy.

>So is this not the same as standard rubbing alcohol?

You can buy 99% alcohol at most drug stores and online. For example:
<http://www.ebay.com/sch/i.html?_nkw=99+isopropyl+alcohol>

> Incidentally I tried this, but no go.

Now that you may have trashed the sensor, try cleaning the PCB (both
sides) around the sensor. Greasy and sooty films tend to cause
leakage problems.

However, I think you're wrong about the humidity sensor. The photo
you supplied is what's used for measuring condensation or dew point.

Most cheap weather stations have humidity sensors made from polymer
film capacitors:
<http://www.epluse.com/en/products/humidity-instruments/humidity-sensor/hc201/>
<https://www.google.com/search?q=polymeric+capacitive+humidity+sensor&tbm=isch>
<http://www.sensorsmag.com/sensors/humidity-moisture/choosing-a-humidity-sensor-a-review-three-technologies-840>

There are also solid state sensors:
<http://www.silabs.com/products/sensors/humidity-sensors/Pages/default.aspx>
However, I haven't seen these appearing in commodity wx stations.
Davis and Adafruit use them (from some other vendor):
<http://smg.photobucket.com/user/AVMan86/media/DSCN4162.jpg.html>
<http://www.adafruit.com/products/1638>

Cleaning a capacitive sensor with alcohol is probably ok, but the
recommended solvent is distilled water. If you've touched the exposed
sensor with your fingers, you might as well use alcohol to clean off
the skin oils.




--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[hon...@yahoo.com]

I briefly considered providing the model # but figured this wasn't all that important since it's unlikely anyone here has the same, and if they do, probably hasn't tried fixing it. But anyway the outdoor sensor is THGR122N.

I was careful not to touch it, and used rubbing alcohol with a cotton swab to clean it. It initially seemed to fix it but then began acting up again. Here's a pic of the sensor in my device: http://postimg.org/image/gw0trmygz/

It appears to match the sensor in the link I originally provided, but I of course I can't say for certain.

I will be trying distilled water since I have that on hand. Would replacing the sensor with one that looks similar likely work? Again, I know nothing about humidity sensors. I know what the answer would be regarding a temperature sensor.

[krw]

On Fri, 10 Jul 2015 20:35:47 -0700, Jim Thompson
<To-Email-Use-Th...@On-My-Web-Site.com> wrote:

>On Fri, 10 Jul 2015 21:59:37 -0400, "Tom Miller"
><tmille...@verizon.net> wrote:
>
>>
>><hon...@yahoo.com> wrote in message
>>news:25ae0c4c-7e00-4215...@googlegroups.com...
>>I have one of those sort-of cheap Oregon Scientific weather stations with
>>the wireless outdoor temperature/humidity sensors. It's maybe about 6 years
>>old, so normally a person would simply buy a new one but I'm not like that.
>>I like fixing stuff rather than tossing it.
>>
>>The outdoor unit senses the temperature just fine, but not humidity. When
>>it's not displaying 2% or 98% for RH, it's displaying another number that is
>>more sane but still wrong. I took it apart and the sensor looks exactly
>>like this:
>>
>>http://www.shinyei.co.jp/stc/humidity_e/images/CL-M53R_L.jpg
>>
>>Any pointers on how these work or what to look for? I've done nearly
>>everything else but humidity. It appears these aren't driven with DC, which
>>makes things more difficult. How probable is it that the sensor simply
>>needs replacing?
>>
>>+++++++++++++++++++++++++++
>>
>>Try cleaning the sensor with isopropyl alcohol, 99% that you can get special
>>order from the pharmacy.
>>
>
>DENATURED Alcohol at most hardware stores.
>

The hardware stores and BORGs here don't carry denatured ethyl, at
least in their paint departments, rather they carry IPA.

[Jeff Liebermann]

On Sat, 11 Jul 2015 13:00:38 -0700 (PDT), hon...@yahoo.com wrote:

>I briefly considered providing the model # but figured this wasn't
>all that important since it's unlikely anyone here has the same,
>and if they do, probably hasn't tried fixing it. But anyway
>the outdoor sensor is THGR122N.

That would be a THGR122NX:
<http://www.oregonscientificstore.com/Oregon-Scientific-THGR122NX-Wireless-Temperature-and-Humidity-Sensor-with-Display.data>
I have a THR268. Very similar electronics inside, but no humidity
sensor. There's a humidity sensor in the BAR888RA base unit, but I
don't want to tear it apart.

It's amazing what one can find with a model number:
<http://www.wxforum.net/index.php?topic=17911.0> (see photo)

>I was careful not to touch it, and used rubbing alcohol with a
>cotton swab to clean it. It initially seemed to fix it but then
>began acting up again. Here's a pic of the sensor in my device:
><http://postimg.org/image/gw0trmygz/>

Much better. Looks like your original photo is an exact match:
<http://www.shinyei.co.jp/stc/humidity_e/main_CL-M53R.html>
"HPR-MQ is a humidity device formed by distributing a humidity
sensitive macro-molecule onto an electrode substrate. The
resistance of the device varies exponentially with variation
on Relative Humidity."
That's new to me as I'm used to such sensors being used for
condensation and dew point, not humidity. Something like this:
<http://www.conrad.com/ce/en/product/187620/B-B-Thermotechnik-CON-SHSA5-SHS-Resitive-Dew-Point-Sensor-Ceramic-mount-plus-interdigital-structure-for-detecting-wate>
I couldn't find any cleaning recommendations, applications info, real
specs, or test circuits.

Interesting that the Oregon Scientific data sheets offers a humidity
range of 5% to 95%, while the sensor data sheet says 20% to 95%.
Hmmmm...

>It appears to match the sensor in the link I originally provided,
>but I of course I can't say for certain.

It's a match. Good find.

>I will be trying distilled water since I have that on hand. Would
>replacing the sensor with one that looks similar likely work?
>Again, I know nothing about humidity sensors. I know what the
>answer would be regarding a temperature sensor.

After distilled water, try a little heat or hot air to evaporate
the water. My guess(tm) is that the ceramic substrate is porous and
you'll need to evorate any absorbed water before it will work again.

Looks like no PCB to clean. However, follow the wires from the
humidity sensor to the PCB and clean up with alcohol and water around
the pads on the PCB. Leakage between the leads is another possible
culprit. However, if there's some kind of wax coating on the PCB,
forget about cleaning it. That's a seal to prevent the PCB from
acting like a sponge and soaking up water. Looking at the photo,
there is a stringy blob of the stuff covering the thin wires going to
the PCB from either the humidity sensor or temperature sensing
thermistor. Leave that alone.

Replacing the sensor might be an option if nothing else works. Looks
like a few sources on Alibaba at $3.00/ea, but nothing from the usual
US distributors. Nothing on eBay or Amazon.

Good luck.

[bloggs.fred...@gmail.com]

That sensor is fairly wild with resistance varying over four decades through the RH measurement range in addition to several thousand ppm change per oC at fixed RH. Manufacturer reference design is simple ac- drive into thermistor compensated voltage divider actively peak detected by OA. If the reading is bouncing around all over the place, I would suspect the peak detector hold capacitor.

[hon...@yahoo.com]

On Saturday, July 11, 2015 at 10:12:01 PM UTC-5, Jeff Liebermann wrote:

> On Sat, 11 Jul 2015 13:00:38 -0700 (PDT), h..gm@y..oo.com wrote:
>
>
> It's amazing what one can find with a model number:
> <http://www.wxforum.net/index.php?topic=17911.0> (see photo)

Yes I found that, but there was no help in that forum.

>
> Looks like no PCB to clean. However, follow the wires from the
> humidity sensor to the PCB and clean up with alcohol and water around
> the pads on the PCB. Leakage between the leads is another possible
> culprit. However, if there's some kind of wax coating on the PCB,
> forget about cleaning it. That's a seal to prevent the PCB from
> acting like a sponge and soaking up water. Looking at the photo,
> there is a stringy blob of the stuff covering the thin wires going to
> the PCB from either the humidity sensor or temperature sensing
> thermistor. Leave that alone.

No conformal coat on this PCB, which is a bit surprising considering it's for outdoors. But then again this is a cheap consumer grade device.

>
> Replacing the sensor might be an option if nothing else works. Looks
> like a few sources on Alibaba at $3.00/ea, but nothing from the usual
> US distributors. Nothing on eBay or Amazon.
>
> Good luck.

I actually found some on eBay that look the same, but without the big "3"; look for HR202L. $3 shipped for 2 from China. It's worth a shot. The specs appear very similar.

After cleaning, currently the reading is stable but the RH is too low (it's super humid here right now, A/C is a great invention). I'll update once I replace the sensor.

[hon...@yahoo.com]

On Sunday, July 12, 2015 at 8:48:30 AM UTC-5, bloggs.fred...@gmail.com wrote:
> That sensor is fairly wild with resistance varying over four decades through the >RH measurement range in addition to several thousand ppm change per oC at fixed >RH. Manufacturer reference design is simple ac- drive into thermistor compensated >voltage divider actively peak detected by OA. If the reading is bouncing around >all over the place, I would suspect the peak detector hold capacitor.

Hmmm, good to know. I never found a decent schematic for this type of sensor. I knew these were AC driven so I thought about hooking my DSO to it but then realized I don't know what I'm looking for. I'll see what happens when I replace the sensor.

[hon...@yahoo.com]

I replaced the sensor with the model I mentioned earlier off eBay, shipped from China for a few bucks, and that fixed it! The RH seems to line up more or less with what is reported by NOAA, which is much better than the abnormally low numbers it was displaying before. It might be off by up to 5% but I don't believe this thing was all the accurate to begin with.

A new unit would have cost about $30, which isn't horrible considering it's at least 6 years old. But repairing something instead of trashing it sure is nice (and at 1/20 the cost). Not much gets thrown out due to breakdown in my house.

[Jeff Liebermann]

On Fri, 24 Jul 2015 04:42:29 -0700 (PDT), hon...@yahoo.com wrote:

>I replaced the sensor with the model I mentioned earlier off eBay, shipped from China for a few bucks, and that fixed it! The RH seems to line up more or less with what is reported by NOAA, which is much better than the abnormally low numbers it was displaying before. It might be off by up to 5% but I don't believe this thing was all the accurate to begin with.
>
>A new unit would have cost about $30, which isn't horrible considering it's at least 6 years old. But repairing something instead of trashing it sure is nice (and at 1/20 the cost). Not much gets thrown out due to breakdown in my house.

Nicely done. Repair is always better than recycling or trashing. I'm
also impressed that you actually found the part. I don't recall the
specs, but 5% is probably better than the sensor accuracy
specifications. Also RH varies radically with height above the ground
(water vapor is heavier than dry air), so don't be surprised if it's
not the same as NOAA.

If you want the official standards, it's probably buried somewhere in
the docs here:
<http://novalynx.com/reference/nfes-2140/>

There's also quite a bit scattered around this web pile on sensor
location and weather station construction:
<http://www.weatherforschools.me.uk>

I'm still having problems believing that the sensor in the picture is
for humidity and not for dew point.

[Phil Hobbs]

On 07/24/2015 01:35 PM, Jeff Liebermann wrote:
> On Fri, 24 Jul 2015 04:42:29 -0700 (PDT), hon...@yahoo.com wrote:
>
>> I replaced the sensor with the model I mentioned earlier off eBay, shipped from China for a few bucks, and that fixed it! The RH seems to line up more or less with what is reported by NOAA, which is much better than the abnormally low numbers it was displaying before. It might be off by up to 5% but I don't believe this thing was all the accurate to begin with.
>>
>> A new unit would have cost about $30, which isn't horrible considering it's at least 6 years old. But repairing something instead of trashing it sure is nice (and at 1/20 the cost). Not much gets thrown out due to breakdown in my house.
>
> Nicely done. Repair is always better than recycling or trashing. I'm
> also impressed that you actually found the part. I don't recall the
> specs, but 5% is probably better than the sensor accuracy
> specifications. Also RH varies radically with height above the ground
> (water vapor is heavier than dry air), so don't be surprised if it's
> not the same as NOAA.

Water vapour is much lighter than air. Air has a mean molecular weight
of around 29 AMU (basically 80% N2 @ 28 and 20% O2 @ 32), whereas water
is 18 AMU. But gases are fully miscible, so they don't separate
meaningfully in the troposphere except by condensation. I suspect it's
proximity to a large reservoir that makes the difference, but that the
altitude effect is probably mostly temperature--I doubt that the dew
point varies as much with height. But then I'm not an atmospheric
physicist.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

[hon...@yahoo.com]

On Friday, July 24, 2015 at 12:35:36 PM UTC-5, Jeff Liebermann wrote:
> On Fri, 24 Jul 2015 04:42:29 -0700 (PDT), hon...@yahoo.com wrote:
>
>
> Nicely done. Repair is always better than recycling or trashing. I'm
> also impressed that you actually found the part.

I can thank Google Images. I don't know how else I would have found it if I couldn't search for "humidity sensor" and look at pictures. Comes in handy for looking for other parts too.

>I don't recall the
> specs, but 5% is probably better than the sensor accuracy
> specifications. Also RH varies radically with height above the ground
> (water vapor is heavier than dry air), so don't be surprised if it's
> not the same as NOAA.

I'm likely stretching it by saying 5%. Without knowing the exact RH at my location I can't say for sure. But it's in the ballpark which is good enough in my situation.

> If you want the official standards, it's probably buried somewhere in
> the docs here:
> <http://novalynx.com/reference/nfes-2140/>
>
> There's also quite a bit scattered around this web pile on sensor
> location and weather station construction:
> <http://www.weatherforschools.me.uk>
>
> I'm still having problems believing that the sensor in the picture is
> for humidity and not for dew point.

There's a clear, slightly sticky layer over the interlocking fingers part of the sensor that apparently absorbs moisture and affects its conductivity. I know it's sticky not because I touched it, but because the two sensors were stuck together in the bag they were shipped in. My guess is this layer went bad on original sensor.

[Techman]

You can check the RH (at least at one point) using some salt and a
sealed container. If you're interested just Google RH calibration salt
and you should find all you need.

[bob.blar...@gmail.com]

I solved this problem with a minimum of fuss.

I opened the external case and carefully opened the compartment that holds the RH sensor and thermistor by cutting through the hotmelt wit a scalpel blade. >>>Be careful of the RH and temp sensor wires!<<< The sensor compartment was full of sticky insect cocoon material. I cleaned it out carefully with a toothpick and Q-tip, while avoiding touching of the sensors. Then I gave it a liberal spraying with CRC QD Electronics Cleaner, which removed any residue. The device works again, reading close to that of a certified Extech hygrometer.