Humidity input bug?

[rossw]

3 months ago I built a force-aspirated temperature and humidity sensor using a WC board, two DS18B20 sensors and the specified Honeywell humidity sensor. Yesterday we had rain for only the second time in 3 months. Temperature plunged rapidly, humidity rose quickly (entirely as expected) - but then the humidity sensor started returning stupid (nonsense) values - I suspect you are not doing any "bounds checking" on the value returned, and if it's over about 98%, your code simply fails and returns 0. (See graphs)
 

 
I would argue this is a bug, and even if the input "shouldn't" go over 100%, returning 0 is far more problematic.

 

[CAI_Support]

Ross,
 
What is your firmware version?  We had changed humidity sensor logic in some later version firmware to not treating just over 100 as false reading. We originally treated anything reading above 100% as false and set that to zero. Now, we realized sensors could have slightly different readings, so that we treat anything reading back slightly above 100% voltage as 100%.

 

[rossw]

Ross,
 
What is your firmware version?  We had changed humidity sensor logic in some later version firmware to not treating just over 100 as false reading. We originally treated anything reading above 100% as false and set that to zero. Now, we realized sensors could have slightly different readings, so that we treat anything reading back slightly above 100% voltage as 100%.

 
Version: v03.02.15

 

[CAI_Support]

Change made in 3.02.16.

 

[XRinger]

I have Version: v03.02.09 and it's been raining for days.. The RH has been 98 to 100 % for a few days now..
Yesterday, the CAI control over my basement ventilation went nuts. RH was displaying "0"..
 
The Vcc to the outdoor pod is 5.02V and the RH input to the CAI is 4.22V  
I think the spec for 100% says 4.07V, not sure.
 
What's the max usable RH voltage I can use with v03.02.09?  
Maybe I can make a voltage divider..  

 

[CAI_Support]

Do you want to update your firmware to the latest one?  We had made changes in our logic will automatically adjust for the input voltage to compensate sensor and resistor differences a year ago.

 

[rossw]

I have Version: v03.02.09 and it's been raining for days.. The RH has been 98 to 100 % for a few days now..
Yesterday, the CAI control over my basement ventilation went nuts. RH was displaying "0"..
 
The Vcc to the outdoor pod is 5.02V and the RH input to the CAI is 4.22V  
I think the spec for 100% says 4.07V, not sure.
 
What's the max usable RH voltage I can use with v03.02.09?  
Maybe I can make a voltage divider..  

 
It is unlikely you will see 0% RH. In my application, I simply check the value and replace 0 with 100. Was a simple kludge that didn't require going out in the field to address the problem and didn't affect the accuracy across the rest of the range.

 

[XRinger]

Do you want to update your firmware to the latest one?  We had made changes in our logic will automatically adjust for the input voltage to compensate sensor and resistor differences a year ago.

 
How would that work?

 

[XRinger]

It is unlikely you will see 0% RH. In my application, I simply check the value and replace 0 with 100. Was a simple kludge that didn't require going out in the field to address the problem and didn't affect the accuracy across the rest of the range.

 
Might see 0% if there was a fire under the sensor..
 also went with the kludge last night, but replaced the 0 with 666 , trying to be funny. Then changed it to 101 in the end. Not too funny.  ^_^ 
 
My first guess was water was dripping right into the holes in the outdoor pod.. 
So, I was outside late at night, in the rain with my flashlight looking under the overhang.. Nope, no water falling on the sensors..
 
Thanks,
Rich

 

[rossw]

Might see 0% if there was a fire under the sensor..
 also went with the kludge last night, but replaced the 0 with 666 , trying to be funny. Then changed it to 101 in the end. Not too funny.  ^_^
 
My first guess was water was dripping right into the holes in the outdoor pod.. 
So, I was outside late at night, in the rain with my flashlight looking under the overhang.. Nope, no water falling on the sensors..
 
Thanks,
Rich

 
 
I built my latest weatherstation with two DS18B20 chips and the humidity sensor all bunched together in the middle of a long tube.
Mounted the tube inside a second, larger tube.
Put a fan and a complete covering cowl over the top and a fine stainless gauze mesh over both ends.
The fan runs slowly and constantly draws fresh air in the bottom and out the top. It would be impossible for rain to get onto the sensors.
Yet during fog (particularly), and with constant rain, I was often seeing %RH toggling between 99% and 0%. With the simple test it has been perfect ever since.

 

[XRinger]

My first attempt at a weather 'pod'  was going to be a RH sensor and a DS18B20 (looks like a transistor)
bunched up on some 4 conductor wire. +5 & Gnd and two sensor wires.
 
But after I soldered on the DS18B20, it seemed to be reading funky, way too high for too long, like it wasn't ever gonna cool off.
So, I turned off the CAI and added another DS18B20 right under it. Turned on the CAI and within a few minutes they were almost in sync. 
Running just fine withing 0.2 or less difference. Then, I soldered the RH on top of the device tree. Insulated the with some tape,
jammed the tree into a 1/2 PVC pipe (pre-drilled with 1/8" holes) and pushed water resistant foam insulation into both ends. 
 
The pair of DS18B20s is on 3 & 4. #1 is the basement temperature and #2 is the hot water tank (DHW).