[werk_ag]

I am also seeing humidity values over 100%. My current humidity display is 106.1%! The humidity of other stations in the area is currently 95-96%. My station has only been running for about a week and in that time the outside humidity readings have been consistantly high by about 10%. The LCD display shows Hn instead of In.

The humidity sensor is a Davis 7346.166 from a Vanatge Pro 2. I beleive that the sensor is a SHT11. I have used as many parts from the old Davis system as I could. All has worked well other than the high outdoor humidity readings. Is it possible for the sensor to output data higher than 100%?

Other than this small problem, the WeatherDuino works great! Thanks for your hard work.

Hi, Rvrlabs

Is good to know that you already have built your WeatherDuino Pro2, and that is working well (almost) with a lot of parts recovered from your used Davis weather station.

I'm not sure about that, but despite the symptoms you describe are the same related by others, (readings of %RH above 100%) your case may have another explanation.

You said you are reusing an SHT11 sensor from your old Davis. I'm not sure, but I think that the SHT11 module used by Davis is made to be povered by around 3,3V. You can also have it powered by 3.3V , from your TX unit, BUT the used library do the calculations based in a 5.0V powered sensor, and this can affect the results. Please try to check that.

There is another possibility for the erroneous readings:
If your SHT11 is a few years old, maybe it is a v3 sensor. By default, the library used by the WeatherDuino Pro2 do the calculations for SHT11 v4 sensors.
You can try edit the library and change the default to v3 sensors.

Code:

// V3 Sensors
  //const float C1 = -4.0;       // for 12 Bit
  //const float C2 =  0.0405;    // for 12 Bit
  //const float C3 = -0.0000028; // for 12 Bit

  // V4 Sensors
  const float C1 = -2.0468;       // for 12 Bit
  const float C2 =  0.0367;       // for 12 Bit
  const float C3 = -1.5955E-6;    // for 12 Bit

[Rvrlabs]

I am also seeing humidity values over 100%. My current humidity display is 106.1%! The humidity of other stations in the area is currently 95-96%. My station has only been running for about a week and in that time the outside humidity readings have been consistantly high by about 10%. The LCD display shows Hn instead of In.

The humidity sensor is a Davis 7346.166 from a Vanatge Pro 2. I beleive that the sensor is a SHT11. I have used as many parts from the old Davis system as I could. All has worked well other than the high outdoor humidity readings. Is it possible for the sensor to output data higher than 100%?

Other than this small problem, the WeatherDuino works great! Thanks for your hard work.

Hi, Rvrlabs

Is good to know that you already have built your WeatherDuino Pro2, and that is working well (almost) with a lot of parts recovered from your used Davis weather station.

I'm not sure about that, but despite the symptoms you describe are the same related by others, (readings of %RH above 100%) your case may have another explanation.

You said you are reusing an SHT11 sensor from your old Davis. I'm not sure, but I think that the SHT11 module used by Davis is made to be povered by around 3,3V. You can also have it powered by 3.3V , from your TX unit, BUT the used library do the calculations based in a 5.0V powered sensor, and this can affect the results. Please try to check that.

There is another possibility for the erroneous readings:
If your SHT11 is a few years old, maybe it is a v3 sensor. By default, the library used by the WeatherDuino Pro2 do the calculations for SHT11 v4 sensors.
You can try edit the library and change the default to v3 sensors.

Code:

// V3 Sensors
  //const float C1 = -4.0;       // for 12 Bit
  //const float C2 =  0.0405;    // for 12 Bit
  //const float C3 = -0.0000028; // for 12 Bit

  // V4 Sensors
  const float C1 = -2.0468;       // for 12 Bit
  const float C2 =  0.0367;       // for 12 Bit
  const float C3 = -1.5955E-6;    // for 12 Bit

Hi,

Thanks for the information. I will check that the sensor is set to 3.3 volts and try changing the library default to the V3 sensor. My Davis hardware is about 6 years old and is most likely the version 3. I will let you know what happens!

[AllanG]

Until now, with the sensors I have, I was unsuccessful in trying to reproduce that behaviour. So, where the problem resides?
Sincerely I don't know! But must be something related to the sensor itself.

Yes, the problem with buying parts very cheaply from China is that we know only what the supplier tells us and we have no way of knowing whether it's true or not. Unless it's a very bad copy, I doubt it's possible to tell if there's a genuine sensiron chip on a board!

Since that one very brief occasion I've not seen above 100% recorded here. I'm going to try a little experiment though. A couple of months ago I bought a SHT25 on a small board which was sold and manufactured here in the UK, so I'm going to install that instead of the SHT21 from China. I'll leave the software as it is now and see if the SHT25 records anything over 100% during the next few months.

Maybe the lesson for us is that it may be a good idea to spend a little more money on some of the critical components to make sure we get genuine and reliable ones!

Happy New Year to the whole WeatherDuino family.

Allan.

[werk_ag]

Hi Allan

I never tested an SHT25, is seems very good. Tell us how it performs.
My votes of a great 2016 year to you too.

[Palmyweather]

Implementing a limitation to 100% it's easy. In next software release, I will implement a check to limit the display value to 100%

Hi there

Could I make an additional suggestion for limit checking in future updates?

Today I needed to briefly unplug my temperature sensor, forgetting to turn off the transmitter. When I checked the display, the temperature had dropped from a nice +25*C to a chilly -40*C which also when though and logged onto my weather station website.

I know it was my own fault for not turning off the transmitter first, but could there be coded protection in the receiver unit that assesses the new temperature reading from the transmitter and says for example "the last value was +25*C, it simply can not drop to -40*C in the next instant, therefore ignore the last reading". This would also help limit any spikes from the cable on the temperature sensor or missed data packets.

I must say however, the new humidity limiting code worked well and stopped it from reading from over 100% while I was undertaking my maintenance.

Just a thought anyway.

[werk_ag]

Hi, thanks for your suggestion...

I really would like to add such and other nice things, but the Nano SRAM is very short... and despite it seems still there is some free, for the system to run stable, we should keep at least 400 bytes of SRAM free, otherwise strange things will start to happen, maybe not in one day or two, but they will happen... I'm sure you understand what I mean.

This is an important hint to everyone who wants to implement some mods on the code.

[Rvrlabs]

I changed the sensor voltage to 3.3vdc and updated the library to the V3 sensor. All is good now. Humidity and temperature readings are back where they should be. I have not seen any humidity readings over 99%. Thanks for the help.

I am also seeing humidity values over 100%. My current humidity display is 106.1%! The humidity of other stations in the area is currently 95-96%. My station has only been running for about a week and in that time the outside humidity readings have been consistantly high by about 10%. The LCD display shows Hn instead of In.

The humidity sensor is a Davis 7346.166 from a Vanatge Pro 2. I beleive that the sensor is a SHT11. I have used as many parts from the old Davis system as I could. All has worked well other than the high outdoor humidity readings. Is it possible for the sensor to output data higher than 100%?

Other than this small problem, the WeatherDuino works great! Thanks for your hard work.

Hi, Rvrlabs

Is good to know that you already have built your WeatherDuino Pro2, and that is working well (almost) with a lot of parts recovered from your used Davis weather station.

I'm not sure about that, but despite the symptoms you describe are the same related by others, (readings of %RH above 100%) your case may have another explanation.

You said you are reusing an SHT11 sensor from your old Davis. I'm not sure, but I think that the SHT11 module used by Davis is made to be povered by around 3,3V. You can also have it powered by 3.3V , from your TX unit, BUT the used library do the calculations based in a 5.0V powered sensor, and this can affect the results. Please try to check that.

There is another possibility for the erroneous readings:
If your SHT11 is a few years old, maybe it is a v3 sensor. By default, the library used by the WeatherDuino Pro2 do the calculations for SHT11 v4 sensors.
You can try edit the library and change the default to v3 sensors.

Code:

// V3 Sensors
  //const float C1 = -4.0;       // for 12 Bit
  //const float C2 =  0.0405;    // for 12 Bit
  //const float C3 = -0.0000028; // for 12 Bit

  // V4 Sensors
  const float C1 = -2.0468;       // for 12 Bit
  const float C2 =  0.0367;       // for 12 Bit
  const float C3 = -1.5955E-6;    // for 12 Bit

[werk_ag]

I changed the sensor voltage to 3.3vdc and updated the library to the V3 sensor. All is good now. Humidity and temperature readings are back where they should be. I have not seen any humidity readings over 99%. Thanks for the help.

I'm glad to know. Thanks for the feedback.

[JT118]

Please advise step by step, how to change to a V3 library. I have, I think, got an older sensor. At first I had reading within a few parts of a degree of the Davis Groweather. When the SHT10 blew up (wrong connections on new TX board) and I replaced with an SHT11 it has always read +0.5C (at 2 to 10C) to + 1C (at 10C to 20C) above other sensors. The SHT25 (Chinese copy I think) has always read a few degrees over but I do not trust this sensor (cable length etc) and have always had it as extra sensor 1 ((0,1) on the RX). Now I have put a few other sensors on the system they are agreeing with the Davis. I must assume that the error is this version difference. Worth trying anyway. But I am a little confused as to how to do this change.

[werk_ag]

Locate the SHT1X.cpp file in your libraries folder.
Open it with a text editor like Notepad++.
Change to this:

Code:

// Conversion coefficients from SHT15 datasheet
  // V3 Sensors
  const float C1 = -4.0;       // for 12 Bit
  const float C2 =  0.0405;    // for 12 Bit
  const float C3 = -0.0000028; // for 12 Bit

  // V4 Sensors
  //const float C1 = -2.0468;       // for 12 Bit
  //const float C2 =  0.0367;       // for 12 Bit
  //const float C3 = -1.5955E-6;    // for 12 Bit

Edited: Forgot to say, you have to reprogram the TX unit again.