Topic: R Humidity way off on my outside unit

[kmahler]

I suspected my outside unit was reading low compared to other stations nearby and the delta between it and the sensor in the display. I know you guys keep your display in the house so the humidity should be very different. But, mine hangs on the wall in the garage near the large garage door. I've been out in the Garage most of the day with the door opened and the delta is significant, 53% on the console and 29% on the outside unit currently. Here is a photo I took earlier of the console.



So I did a little test today. I have a digital Hygrometer I use for my Humidor. I used it as a guide as to which of the two was way off. It turned out to be the outside unit. In the above photo the small Hygrometer is next to the console. They are pretty close at 53% to 56.1%. I then put the small Hygrometer in the radiation shield with the outside unit for about an hour. Before taking it out I took another pic of the console showing the reading from the AW sensor. Then I walked right around the house to the station and removed the small unit. The console was reading 29% and the small unit was reading 53.6%. Does anyone know how to calibrate the RH on the outside unit?

[CW2274]

I'm not an Ambient owner but am confident calibration will get you no where because the error is so significant. You could adjust it, but it'd be pretty much like a broken clock, right only twice a day, then it's way too high or way too low. Sensor replacement is probably your only option.

[DanS]

If you look inside and it uses the resistive type of humidity sensor there's hope. Nowadays, stations almost always use the digital type though and I agree that you would have to replace it.

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[kmahler]

As an added oddity. Now that it's evening, the internal and external sensors (remember the internal is actually in the garage) are within 2% of each other. Earlier today they were off by 24% even though they are both exposed to the outside air.

[DanS]

I guess the ultimate test would be placing the outside unit right up next to the garage mounted console for a couple hours.

My console is inside but all the windows stay open 24/7/365. The outdoor sensor is about 40 feet or so away and get big differences some times and very close other times. When I lay both next to each other for a couple hours they even out.

[kmahler]

I guess the ultimate test would be placing the outside unit right up next to the garage mounted console for a couple hours.

Great idea DanS I was going to do that today anyway. I did so and they are still way off. I had the external unit sitting about 8 inches from the console for several hours today. I then placed it on top of the console just for the picture. Here you can see the console and the external unit together showing the large delta in RH%.



So then I took the outside unit apart. Below are pictures of the circuit board. The only sensor of any type I see on the board is the white box so I'm assuming it's one of the many combo Temp + RH% sensors.

The sensor itself has two contacts going to the small board. Then the small board has a chip on the back side which then connects to the main board with four connections. Could this be an I2C connection? The CPU and another chip on the main board are protected by epoxy so I cannot find out what they are. I know I can purchase another transmitter with a new sensor for $29 from amazon. But, If possible I'd like to install a different sensor on the board if there is reasonable hope it would work.

[DanS]

If that white box has only a meshed comb grid inside (like the top image in my previous post) that would be the humidity sensor. A gel compound on it (hygroscopic gel) is what is losing it's properties causing your readings to be off. I've been trying different compounds on an old sensor I have here to see what replacement gel works best. I've found various skin cosmetic and hair hold/mousse gels that contain an ingredient call PEG# work well. The lower the PEG# (number) the better the results' ie..,  PEG6 much better than PEG400. I recently found out that Zinc Oxide may be another option and waiting for some to arrive and try out. Fun to experiment with anyway.

maybe try a toothbrush moistened with rubbing alcohol to brush the white buildup off the board especially around where those 4 pins come through. Couldn't hurt.