Topic: Measuring Temp/Hum using two different sensors/shields with Weather Display

[hwcorder]

So I wasn't sure which thread to put this in the Radiation Shield or SHT31 Reliability, so I just started a new one.
I have found a way to measure temperature and humidity using two different sensors in two different radiation shields using the Advanced/Misc Settings option in Weather Display (WD).

You can substitute the main display readings from a second temp/hum station.  For example my current setup I placed the sht31 back in my FARS unit and am using that for temperature.  I have had an sht75 probe which I put together and inserted it into the MeteoPro passive shield which I have been testing against the Davis FARS for a few days now.  Using the advanced setup tab which is under the setup menu in the WD main screen then click the Temp / Hum / Extra Temp / Custom Vertical Meter / Black Globe Temp tab.  About 3/4 of the way down you will see this.
Use this extra temp sensor # for Davis VP outdoor temp (0 for not in use (defualt)).
Use this extra hum sensor # for Davis VP outdoor hum ( 0 for not in use).
Replace the 0 with whatever number station your extra temp/hum sensor is. 

For example I have switched the humidity reading in the main window on WD to my temp/hum station 1.  WD is now using the temperature from the 31(FARS) and the humidity from the 75(passive) to calculate my dewpoint temperature.  This is similar to ASOS which measures the temperature in a FARS and dewpoint using a sensor housed in a passive shield.  For those of you maybe not familiar with some of the resent conversations on this board it has been shown that active aspiration can rapidly age temp/hum sensors and throw them out of specs at least in humid climates. More so with the humidity readings then temperature.     

I will still do temperature comparisons on the shields. Right now as both are still heavily shaded the FARS is reading 81.2 and the MeteoPro 81.3.

[dendrite]

Interesting. That's along the lines of what I would like to do. FARS/75 for temp and dewpoint in a separate passive.

The only caveat is that I wanted to provide light supplemental heat inside of the passive shield to prevent the SHTxx from ever approaching condensation. I'd use the dewpoint from that and the temp from my FARS to calculate a new RH to send to CWOP.

I know Brian from WD is pretty flexible with his customers so maybe he could make an update for me with that option.

Not to jump into your thread with my own question, but is it possible to add a small resistor to the temp/hum voltage line to provide a little heat? I figure the sensor is getting a steady supply of voltage so the current will change. All I really need is enough heat to keep a dewpoint depression of at least 5F (80% RH). Where I live, if there's wind, usually it's accompanied with drier air anyway. So during those high RH times (precip or rad cooling) the wind is usually light and the supplemental heat should do its job. Maybe a resistor that will put out 5-10W? What does the voltage to the sensor usually run at? ~3V?

Again, not trying to steal your thread. It's just running tangent to the ideas I have in my head right now. Nice find though. I may have to pony up for WD. I just wish I could get 0.1F resolution with the 2nd sensor.

[hwcorder]

Interesting. That's along the lines of what I would like to do. FARS/75 for temp and dewpoint in a separate passive.

The only caveat is that I wanted to provide light supplemental heat inside of the passive shield to prevent the SHTxx from ever approaching condensation. I'd use the dewpoint from that and the temp from my FARS to calculate a new RH to send to CWOP.

I know Brian from WD is pretty flexible with his customers so maybe he could make an update for me with that option.

Not to jump into your thread with my own question, but is it possible to add a small resistor to the temp/hum voltage line to provide a little heat? I figure the sensor is getting a steady supply of voltage so the current will change. All I really need is enough heat to keep a dewpoint depression of at least 5F (80% RH). Where I live, if there's wind, usually it's accompanied with drier air anyway. So during those high RH times (precip or rad cooling) the wind is usually light and the supplemental heat should do its job. Maybe a resistor that will put out 5-10W? What does the voltage to the sensor usually run at? ~3V?

Again, not trying to steal your thread. It's just running tangent to the ideas I have in my head right now. Nice find though. I may have to pony up for WD. I just wish I could get 0.1F resolution with the 2nd sensor.

No problem, I have also thought about supplemental heating of the second sensor, but like you stated we would have to find a program that could use the dewpoint to calculate RH like ASOS does and yes it would be great if Brian could help us out there.  I'm by no means an electronics expert so somebody else can weigh in here but adding a resistor should give you the result you are looking for I would think.  According to the spec sheet from senserion the supply voltage can run from 2.4 to 5.5V with 3.3V being typical.

[dendrite]

Interesting. That's along the lines of what I would like to do. FARS/75 for temp and dewpoint in a separate passive.

The only caveat is that I wanted to provide light supplemental heat inside of the passive shield to prevent the SHTxx from ever approaching condensation. I'd use the dewpoint from that and the temp from my FARS to calculate a new RH to send to CWOP.

I know Brian from WD is pretty flexible with his customers so maybe he could make an update for me with that option.

Not to jump into your thread with my own question, but is it possible to add a small resistor to the temp/hum voltage line to provide a little heat? I figure the sensor is getting a steady supply of voltage so the current will change. All I really need is enough heat to keep a dewpoint depression of at least 5F (80% RH). Where I live, if there's wind, usually it's accompanied with drier air anyway. So during those high RH times (precip or rad cooling) the wind is usually light and the supplemental heat should do its job. Maybe a resistor that will put out 5-10W? What does the voltage to the sensor usually run at? ~3V?

Again, not trying to steal your thread. It's just running tangent to the ideas I have in my head right now. Nice find though. I may have to pony up for WD. I just wish I could get 0.1F resolution with the 2nd sensor.

No problem, I have also thought about supplemental heating of the second sensor, but like you stated we would have to find a program that could use the dewpoint to calculate RH like ASOS does and yes it would be great if Brian could help us out there.  I'm by no means an electronics expert so somebody else can weigh in here but adding a resistor should give you the result you are looking for I would think.  According to the spec sheet from senserion the supply voltage can run from 2.4 to 5.5V with 3.3V being typical.

Ditto on the electronics.



So R = V²/P

But I = V/R

So if we keep a constant voltage and increase the resistance, the current has to drop? We'd just need to keep it high enough for the sensor specs. I'm sure someone more knowledgeable on this than me can chime in.