Humidity measure falls to 0 when reaching 100%

Hello

I have a domestic HVAC system in my house.

In my basement, I've installed the Honeywell HH4000 sensor in the pipe that takes the wet air from bathroom (+/-15m far away from bathroom)

This sensor is connected to webcontrol Humidity entry.

I measure, when we take a shower, an increase of humidity, that is normal

But the value reaches 100% very rapidely and then falls down to 0% for a while

Check here, you will see the spike and return to 0% very often : https://www.thingspeak.com/channels/3280


It's like the hulidity sensor is saturated ?

Any idea of the root cause ? I have protected the Honeywell sensor with a small coton cover.

Thank you

When humidity reaches to the 100%, if the sensor output any higher, it will cause AD result becoming negative number.
You can add a small resistor 1k to 10k range in the center pin of the humidity sensor, so that its output is reduced little bit, then humidity output will not go beyond 100%.

Thank you. I will add this resistor between sensor output and ground to test.

Please note that I have also some strange fluctuations with DS1820 Temperature sensors: the value changes +/1°c every measure.

have a look on "T1"
https://cosm.com/feeds/80285

I don't have this behaviour on all Temp. See T2,T3,T4... on COSM page sensors. Any idea of the root cause ?

Thomas

Can you add a 470uF 16V capacitor like this http://www.ebay.com/itm/260824182372
to the pins between the terminal 1 and 3 of the temperature or humidity sensor to see if that helps?

We noticed that the noise in the power line is the main cause of the inaccuracy measurement of A/D and other. Adding a capacitor in parallel in terminal pin 1 and 3 will effectively help filter the 5V incoming power noise.

CAI_Support said:

Can you add a 470uF 16V capacitor like this http://www.ebay.com/itm/260824182372
to the pins between the terminal 1 and 3 of the temperature or humidity sensor to see if that helps?

We noticed that the noise in the power line is the main cause of the inaccuracy measurement of A/D and other. Adding a capacitor in parallel in terminal pin 1 and 3 will effectively help filter the 5V incoming power noise.

Click to expand...

I will try but strange as all Dallas temp sensors are together and some give stable values and others fluctuating value

The microcontroller in Dallas sensor might be in different batch with different design.

CAI_Support said:

When humidity reaches to the 100%, if the sensor output any higher, it will cause AD result becoming negative number.
You can add a small resistor 1k to 10k range in the center pin of the humidity sensor, so that its output is reduced little bit, then humidity output will not go beyond 100%.

Click to expand...

Hello

I tried with 4700ohms resistor but measure drops to 0% always

Then I increase gradually the resistor but when I get again correct measures, the sensor is still saturating when reacing 100% and drops to 0% again...

I think there is a problem in the firmware

Thomas

Hi Thomas,

The firmware will check if the output is beyond 100%. If the humidity sensor is greater than 100%, it does not believe the result. That is why you see if display 0.
What value resistor you added in? R12 is a 100K resistor for dividing the humidity sensor output. I think you should keep increase its value till it will not get to beyond 100%.

Thanks,

Hello Strangely, this problem is back, on my WC8. Do you have a electtronic scheme showing how the HH4000 is conenctected to CPU ?
 
Thomas

In HW rev 2.3.8 board, there is a capacitor filter on board already, so that humidity reading is very stable.   Humidity sensor is going through two resistors divide then feed into CPU pin to convert to A/D. In the past, we did have other customers reported the HIH4000 sensors sometimes gone bad over the time. Maybe you can try another humidity sensor to see if that helps

CAI_Support said:

In HW rev 2.3.8 board, there is a capacitor filter on board already, so that humidity reading is very stable.   Humidity sensor is going through two resistors divide then feed into CPU pin to convert to A/D. In the past, we did have other customers reported the HIH4000 sensors sometimes gone bad over the time. Maybe you can try another humidity sensor to see if that helps

Click to expand...

I've Board 2.0.2. I've already changed the HiH4000. does not help.
Possible to tell me where exactly should I install capacity (value ? between data pin & GND i presume ) and extra resistor ?
 
Thank you

On R13, adding a 0.1mF capacitor will help smooth out jitter on humidity input.  However, there are so many hardware changes in later hardware revisions.  For example, 2.3.8 hardware fully tested in above 70C running environment, that alone is a big plus for many installations.

CAI_Support said:

On R13, adding a 0.1mF capacitor will help smooth out jitter on humidity input.  However, there are so many hardware changes in later hardware revisions.  For example, 2.3.8 hardware fully tested in above 70C running environment, that alone is a big plus for many installations.

Click to expand...

 
hello
 
can you summarize which hack should I do on WC8 HW V2.2.2 and WC32 HW V5 to improve behaviour (stability + non saturation) ?
thanks