Humidity Bounce

[CAI_Support]

Humidity sensor is different from most other sensors, it is exposed to the air and humidity.  The oxygen in the air as well as humidity will corrode the sensor elements.  Our experience with this sensor is that it may last 3 to 5 years. If the sensor output start jumping up and down, it is time to replace it.
 
We calibrated the Honeywell sensor output using chemical chambers. That process is long and expensive.  That curve is stored in our firmware, so that input is adjusted for proper display.  From 3.02.16 firmware, we also added auto adjustment feature for the humidity sensor input to compensate the differences from resistors and sensors.  Adding resistor divider and capacitor may affecting the accuracy of the reading.

 

[XRinger]

Thanks for the info. I'll start looking for a new sensor. I guess letting the sensor sit unused in the basement for ~2 years wasn't good for it. 
(When it was delivered, it wasn't inside a sealed package).
It may have been dying of old age before I got it. Since it's always been bouncy..
 
I need something that reads RH within 10% to 15%, or the basement ventilation part of my  project will fail..

 

[XRinger]

Found one that seems cheaper.. Maybe hook it up to a A/D input and DIY calibrate. All I need to dectect 70% RH..
 
http://www.newark.com/jsp/search/productdetail.jsp?SKU=11R0670&CMP=KNC-GPLA&mckv=|pcrid|27090074181|plid|
 HONEYWELL S&C - HIH-5030-001 - IC HUMIDITY SENSOR, 3.3V, SMD
 
The spec says 5.5V max operating voltage.. Just has lower sense output..
 
Anyone have experience with it?

 

[CAI_Support]

Found one that seems cheaper.. Maybe hook it up to a A/D input and DIY calibrate. All I need to dectect 70% RH..
 
http://www.newark.com/jsp/search/productdetail.jsp?SKU=11R0670&CMP=KNC-GPLA&mckv=|pcrid|27090074181|plid|
 HONEYWELL S&C - HIH-5030-001 - IC HUMIDITY SENSOR, 3.3V, SMD
 
The spec says 5.5V max operating voltage.. Just has lower sense output..
 
Anyone have experience with it?

Interesting, this one is designed for 3V, but it may work for 5V, since its max voltage is 5.5V.  The concern is the output curve, that may or may not match the one we have tested.  However, it may provide stable reading, as long as you know what would be the reading for 70% with this sensor,

 

[XRinger]

When I searched and saw the HIH-5030-001 a few prices were displayed..
I should have looked a little deeper. I don't think single unit prices are very good..
 
This afternoon, I was looking at the old analog (no battery required) RH gauge.
and started wondering if I could use an TCRT5000 sensor to 'see' the indicator needle.
 
Last year, in an experiment to detect Ice, I tested an IR reflector type sensor using the RH sensor input on my CAI board
and it seemed to work pretty well..  Maybe it could see a mechanical indicator with a small reflector,
that would move in front of the sensor..
 
http://ecorenovator.org/forum/geothermal-heat-pumps/2412-automatic-defrost-circuit.html
 
Too Rube Goldberg?
 
Cheers,
Rich

 

[CAI_Support]

Adding a protection block in front of the HIH sensor, so that it will not directly hit by water drop, light ray, or dust, that will help the sensor last lot longer.

 

[XRinger]

My RH sensor is inside a 1/2" PVC tube, sealed on both ends, with a few 1/8" holes for air flow.
It's installed about 2.5 feet off the (dry)ground, well back under a solid structure, so that rain and snow can't hit it.
 
It's not shielded from dust. When I make the next one, I'll line the tube with Tyvek to keep out the dust.
It might react slower, but I'm not real interested in picking up a rapid RH change,
since once the fan starts, the sample rate drops to 4 times an hour.

 

[CAI_Support]

I see. If it is sealed in a tube and sensing surface face down, it should be well protected. A lot of higher end thermostat A/C control has this sensor inside, they seem last long time..

 

[XRinger]

That's good news. I might not have to replace this for while..
We had a pretty dry day today.  And oddly, the RH was only bouncing 1 or 2 percent today.
Now that it's late at night and 88% RH outdoors, it's still very stable at 1 to 2 percent bounce..

 

[CAI_Support]

Interesting.  I don't know if that means the sensor had something on its surface before yesterday?
We have humidity sensors gone bad in our lab before, we tossed them out. Maybe we should clean then and let them dry out to see if that helps.

 

[XRinger]

 
It was really wet last week and I think some moisture may have accumulated in the probe and there may have been droplets on the sensor elelement..?.
When the dew-point is equal the air temp, (as it was on the 7th) everything out there can get wet.. 
Today is cool and overcast. RH is now bouncing between 86 & 87%  Which is likely normal operation..
 
See data here.. Those pictures seem to be updating..
http://pauland.net/wxwuhistory.php?ID=KMAWOBUR2&month=10&day=9&year=2013&units=E&mode=2

 

[CAI_Support]

Nice chart and great web site!
 
What can we do to make this working better for you, so that when this happened, you don't get bounced reading?  It seems WC8 is reading from sensor whatever it provides. If there is someway to tell that bounces were caused by the droplet, so that when this extreme condition happened, it would stay up at 100% instead of following the sensor?  I heard before that some pressure sensors would do similar thing when RH reached 100%.

 

[XRinger]

That site is only about 1/2 a mile from me, at a similar elevation, so I like to use it as a quick calibration source.
 
When I went outdoors this morning at 8:15AM, the RH was around 100% and the dewpoint was at air temp..
I couldn't see droplets on the PVC deck railing, but when laid my hand on the rail, it had a very thin coating of cool water all over the top surface.
I think that's because the PVC has thermal Mass. It stays colder than the air temperature, so condensation forms.
 
If the temperature inside the sensor tube was 45F and the outside dewpoint started to climb, (as air temp climbed toward 55F)
Any warmer air entering the sensor tube would likely condensate on all the cool surfaces. (cool running devices).
If I took a cold beer out outside and sat it on the rail, it would be soaking wet within seconds..
 
Humm, I need a beer..
 
 
I think the main problem is with the matching of the sensor to the calibration of the CAI firmware. That's fixed in newer versions.
When water coats the sensor, it goes to it's limit, and provides it's max voltage output. And that's just a tad too much voltage..
Instead of displaying 102% RH, it defaults to zero. I use PLC code to turn that zero into 101 for my code use and it works fine.
 
Bottom line:
It must be dew on the sensor. Makes it go to max output voltage.. Results in over 100% RH..
 

 

[Tschmidt]

Now that it's late at night and 88% RH outdoors, it's still very stable at 1 to 2 percent bounce..

I'm using the Honeywell in our greenhouse and during the winter humidity gets pretty high when temperature goes down. Have not noticed a problem.
 
BTW what software are you using to graph the humidity? My winter project is to pretty up the user interface on the WebControl and present historical data.
 
/tom

 

[XRinger]

I don't how these sensors work, I just assume they don't like water splashed right on the sensor element.
My Honeywell sensor came from Ebay, so it might be a clone for all I know.
Or it might have been from the Honeywell production line Reject box.?
 
The plots I use all the time, are from a friend who lives a few blocks over. He's got a weather station.
http://pauland.net/wxdaily.php
It has 'Local' historical data and I've found it very useful for looking at the very local weather in real-time.. 
I really like the Radar page, since it has a Visible Satellite button (Vis Sat at the bottom of the page)
that shows the clouds. Stuff you can't see on Radar. Nice for predicting solar condix..