Weather board 2 time response

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Weather board 2 time response

Unread postby bournej » Fri Jun 09, 2017 2:42 am

I have about 8 weatherboard 2 sensors hooked up with a i2c multiplexer to handle the fixed address. When observing the humidity data I notice that the response time of the green data line is significantly lower. The bme280 data sheet says its humidity sensor response time is 1s (tau 63%), however I am finding that this can vary a lot. I have tried running different configurations of weather boards and it seems that a slow sensor is consistently slow without any dependency on the number of sensors or the ordering of the sensors in the multiplexer. I have briefly looked into the bme280 api, but does anyone know if I have a calibration issue or just faulty sensors. I have bought 25 sensors in total and 8 of them I consider fast 1s response times and the rest are slow where the response times are roughly 10 seconds or more. Any ideas are greatly appreciated.

Screenshot from 2017-06-08 11-41-17.png
humidity data
Screenshot from 2017-06-08 11-41-17.png (1.62 MiB) Viewed 1129 times
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Re: Weather board 2 time response

Unread postby odroid » Fri Jun 09, 2017 10:32 am

We've not tested the time response.

Can you check "Forced mode" and "Normal mode" as described on Datasheet Page 13?
Also try to disable oversampling option on "pressure" for 1Hz sampling on Datasheet Page 17.
https://ae-bst.resource.bosch.com/media ... 001-11.pdf
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Re: Weather board 2 time response

Unread postby bournej » Sat Jun 10, 2017 1:30 am

I run this snippet of code for each sensor.

Code: Select all
if(bme280_begin(device)<0){
std::cerr<<"bme280 failed on sensor: "<<j<<std::endl;
return -1;
}
else{
bme280_set_power_mode(BME280_NORMAL_MODE);
bme280_set_oversamp_pressure(BME280_OVERSAMP_SKIPPED);
}


I have verified that the function bme280_set_* returns 0 for each sensor which implies success. However this doesn't change the time response of the slow sensor or any sensor from what I can notice.
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Re: Weather board 2 time response

Unread postby odroid » Fri Jul 14, 2017 1:13 pm

Sorry. I forgot this topic.
I think some of BME280 sensors could be damaged and it slowed down the response time.
In the SMT process or cleaning process, the humidity reading parts could be coated/polluted by extra particles even I am not sure.

Can you try to clean the sensors by dipping the slow sensor boards into a cup of clean Alcohol?
If possible, hardly shake the sensor board in the cup to remove the particles.
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Re: Weather board 2 time response

Unread postby bournej » Sat Jul 15, 2017 5:27 am

I measured the response of two humidity sensors, one fast and one slow. I am mainly concerned with the initial rise time of the sensor. As you can see the one is slower than the other when applying humidity and restoring from a high humidity. I have some "slow" sensors that are much slower than the one in the figure.
before_Acetone.png
before_Acetone.png (96.02 KiB) Viewed 977 times


I dipped the slow wb sensor into acetone about 4-5 times and let it dry out for about 5-10 min.
after_Acetone.png
after_Acetone.png (94.29 KiB) Viewed 977 times


The first thing I notice is that the bias of the sensor is much different and maybe a little bit faster of a response (its hard to tell). Acetone is the only thing I had on hand, but will try alcohol later.

I am probably just going to order more of these sensors, is there anyway you guys can ensure that the response of the sensor is as described in the data sheet (i.e. 1 sec.)?
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Re: Weather board 2 time response

Unread postby odroid » Sat Jul 15, 2017 10:56 am

Please don't try the Acetone. It will damage the sensor probably.
Use clean Alcohol and dry the sensor board.
I still think the very thin extra particle might cover the sensor and it slows down the response time perhaps.
Because we don't have any equipment(chamber) to change the humidity quickly, it is really hard to check the response time on our side.

Please try Alcohol cleaning and let me know the result.
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Re: Weather board 2 time response

Unread postby bournej » Tue Jul 18, 2017 4:57 am

Good to know. And BTW I don't have any chamber equipment either, I have been using my thumbs to apply a "step" input in humidity by pressing them onto the active sensors. So there could be some discrepancies between my thumbs, but I doubt this have much of a difference.

Before alcohol, comparing 1 slow and fast sensor.
before_Alcohol.png
before_Alcohol.png (96.66 KiB) Viewed 935 times


So I tried alcohol by dipping the slow sensor and rubbing it with a paper towel.
after_alcohol_1.png
after_alcohol_1.png (93.65 KiB) Viewed 935 times


I notice a slight difference in the response but still is slower so I try again.
after_alcohol_2.png
after_alcohol_2.png (91.81 KiB) Viewed 935 times


I don't think there is much of a difference, but I try again a couple of more times and the response still is much slower than the fast sensors.

For comparison, here are two fast sensors and so this is what I want my slow sensors to look like.
two_fast.png
two_fast.png (77.78 KiB) Viewed 935 times



I am probably just going to order more of these sensors, is there anyway you guys can ensure that the response of the sensor is as described in the data sheet (i.e. 1 sec.)?
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Re: Weather board 2 time response

Unread postby odroid » Tue Jul 18, 2017 11:45 am

Thank you for the test.
Did you use only your thumb to block the hole on the sensor? :o
Any other method to block the hole to reduce the side effect of a warm finger?

Anyway, we will try the thumb blocking soon.
How many sensors do you need more?
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Re: Weather board 2 time response

Unread postby bournej » Tue Jul 18, 2017 11:58 am

Basically, I would try to get both my thumbs the same temperature by pressing them together for a couple of seconds and then directly pressing them onto the two humidity sensors specifically the BME280. So to answer your question, yes my thumbs were blocking the hole on the sensor. I don't think this is the issue though, because I have tried just breathing on both sensors and still have a slower respond on some sensors and fast on others.

Maybe 20 sensors. I need 25 total for a sensor grid, and at least 3 more for some differential drive robots. I have about 8 sensors (from the original 25 sensor PO) are fast; the rest are slow.
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Re: Weather board 2 time response

Unread postby bournej » Fri Jul 28, 2017 2:39 pm

Have you guys figured anything out?
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Re: Weather board 2 time response

Unread postby lsc1117 » Fri Jul 28, 2017 8:05 pm

Hi,

We tested WEATHER-BOARD2 the way you used it.
But, the temperature and humidity environment in our office is not stable.
so, we'll test again next week.
wb2_test.png
wb2_test.png (289.63 KiB) Viewed 820 times


But we think 4 of 10 seem to have slow response time as you observed.
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Re: Weather board 2 time response

Unread postby bournej » Tue Aug 01, 2017 12:51 am

lsc1117 wrote:Hi,

We tested WEATHER-BOARD2 the way you used it.
But, the temperature and humidity environment in our office is not stable.
so, we'll test again next week.
wb2_test.png


But we think 4 of 10 seem to have slow response time as you observed.


Thank you Isc1117 for validating my observations of the performance of the weather board 2 sensor. Correct me if I am wrong, but would the instability of the temperature and humidity of your office have a drastic effect on the performance of the weather board 2 sensor?
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Re: Weather board 2 time response

Unread postby odroid » Tue Aug 01, 2017 9:23 am

I don't think so. So the test result seems to be enough to screen slow sensors.

Once you order the sensors, let me know your Order Number via PM.
We will collect faster sensors and ship it to you.
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Re: Weather board 2 time response

Unread postby bournej » Thu Sep 28, 2017 4:24 am

odroid wrote:I don't think so. So the test result seems to be enough to screen slow sensors.

Once you order the sensors, let me know your Order Number via PM.
We will collect faster sensors and ship it to you.



Do I need to order from a specific vender?
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Re: Weather board 2 time response

Unread postby odroid » Thu Sep 28, 2017 9:23 am

No. you can order from our e-store and let me know the order number via PM.
http://www.hardkernel.com/main/shop/goo ... hp?lang=en
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