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Where to mount the Temp/Humid sensor?
#1
Hello all,
Doing some more planning for the build and placement of the WeatherDuino TX unit and had a thought.

Where should I place the temp sensor to get an accurate reading?

I currently have a Fine Offset weather station that's mounted on top of a poll about 20 feet in the air. I believe the temp sensor in it is under the rain gauge and inside a 'radiation shield'. Is this the best place to mount my new SHT31-D temp/humid sensor (I assume that's the recommended sensor)? Would it be better placed somewhere nearer ground level in the shade?

I guess the concept of an accurate temperature is a bit open to interpretation... should the temperature be at 20 feet in the air in the sun or at ground level in the shade?
I guess what I'm saying is that I'm sure the reading the sensor takes will be accurate, I'm just not sure where a 'real' temperature should be measured... if that makes any sense!! 

What do you think?
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#2
Pretty good summary to where to place things here: https://www.wunderground.com/weatherstat...nguide.asp
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#3
(05-01-2019, 01:06)uncle_bob Wrote: Pretty good summary to where to place things here: https://www.wunderground.com/weatherstat...nguide.asp

That's a pretty good summary UB Smile
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#4
(05-01-2019, 01:06)uncle_bob Wrote: Pretty good summary to where to place things here: https://www.wunderground.com/weatherstat...nguide.asp

Thanks very much, I'll try to keep that all in mind as I decide where to put this.

Cheers,
Gord
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#5
(04-01-2019, 23:14)WetCoast Wrote: ... Is this the best place to mount my new SHT31-D temp/humid sensor (I assume that's the recommended sensor)? Would it be better placed somewhere nearer ground level in the shade?

Just a note: Connect the SHT31-D sensor only to the I2C port on the TX interface. If you need to use a long cable (more than 2 or 3 meters) you can use the Extended I2C port, but in this case you will need to use another I2C bus extender chip at the end of the cable. Connecting the SHT31 sensor directly to the EI2C port will reduce their life significantly.

Some older models of the SHT31 modules have level shifters on the module board, these ones (realy hard to find nowadays) can safely be connected directly to the EI2C port without using a second I2C bus extender chip.
MeteoCercal - Air Quality Data
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#6
Are you meaning in regard to it being 5v levels due to the extended bus?

I have made sure that any modules I buy are 5v compatible such as this one from Adafruit. Or is there another issue to be aware of?

https://www.adafruit.com/product/2857
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#7
(05-01-2019, 09:23)41south Wrote: Are you meaning in regard to it being 5v levels due to the extended bus?

I have made sure that any modules I buy are 5v compatible such as this one from Adafruit. Or is there another issue to be aware of?

https://www.adafruit.com/product/2857

Its not about the voltage, its about the current required on the Extended I2C bus.

After having noticed a considerable drop on the lifetime of the new SHT31 modules, engolling and t3gathome, did a research on this matter, and have concluded that the SHT31 chip can only drive 5mA while the Extended I2C bus may require up to 30mA.
Older models of the SHT31 modules used some transistors to act as levels shifters, those transistors can deal with the current required by the Extended I2C bus, that's why they can work connected directly on the EI2C port.

I trust on the engolling and t3gathome conclusions, that's why I'm talking about it.
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#8
Many thanks. I did some reading afterwards and concluded that the bus current must have been the issue. I will read more but should be able to avoid using the extension bus.

Thanks again for the information.

Colin
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#9
For those (many of us) who may need to use long cables between the TX and the T/H sensor, I'm designing a very small adapter, which includes a second I2C bus expander chip. The design will allow the mounting of the SHT31 sensor on the adaptor, so connections remain the same.
This adaptor should be available in one or two months.
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#10
Thumbs Up 
(05-01-2019, 23:53)Werk_AG Wrote: For those (many of us) who may need to use long cables between the TX and the T/H sensor, I'm designing a very small adapter, which includes a second I2C bus expander chip. The design will allow the mounting of the SHT31 sensor on the adaptor, so connections remain the same.
This adaptor should be available in one or two months.

Smile
Best Regards
Zdenek

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