Correcting data readings of humidity, temperature in building project

rossoreed

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May 17, 2018
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Correcting humidity data readings

I'm trying to find a formula that can help me with a project I'm building and hope that you can help.

I'm taking humidity data readings through sensors, but have found errors occurring as the humidity sensors are temperature sensitive, and need to add temperature compensation to ensure the readings remain accurate.

For example, at 20 deg C, the humidity sensor reads 270, whilst at 30 degrees C, the same sensor reads 237. Both sensor readings should be identical.
Unfortunately, the error is not linear, as the error percentage reduces as the temperature increases.

Any formula would be included within the computer software, but having wrestled with this most of tonight, I have not got anywhere near a solution or a way forward.
:sad:

It's time like this that I wish I'd paid more attention in class!!
 
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Subhotosh Khan

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I'm trying to find a formula that can help me with a project I'm building and hope that you can help.

I'm taking humidity data readings through sensors, but have found errors occurring as the humidity sensors are temperature sensitive, and need to add temperature compensation to ensure the readings remain accurate.

For example, at 20 deg C, the humidity sensor reads 270, whilst at 30 degrees C, the same sensor reads 237. Both sensor readings should be identical.
Unfortunately, the error is not linear, as the error percentage reduces as the temperature increases.

Any formula would be included within the computer software, but having wrestled with this most of tonight, I have not got anywhere near a solution or a way forward.
:sad:

It's time like this that I wish I'd paid more attention in class!!
These types of corrections are dependant on the manufacturer. I suggest you contact them.
 

rossoreed

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May 17, 2018
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These types of corrections are dependant on the manufacturer. I suggest you contact them.
There is no manufacturer as this is a project which I have built to monitor soil humidity in my greenhouse, and the sensors are simply metal probes.

Isn't there a formula for this type of problem?
 

rossoreed

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May 17, 2018
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After some further testing, I have some data which explains the error better.
As the temperature increases, the moisture reading increases exponentially. I am hoping to apply compensation to the moisture reading so that the moisture reading remains constant (should be 81.75)

CHART.jpg

The actual data is;

Temp Moisture
10 81.75
15 83
20 85
25 87.7
30 91
35 95
 

stapel

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Isn't there a formula for this type of problem?
One formula to correct for all possible errors in all types of sensors? I wish! :p

Since, by its very nature, you're working with something that is going wrong, then there can't be a nice, neat formula for "correct" values. Instead, you'll have to decide what all inputs are relevant, take many measurements, and then try doing something like a statistical regression, to create a custom equation for your custom situation. Good luck! ;)
 

rossoreed

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May 17, 2018
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I'd like to say thanks for the help, but unfortunatly there hasn't been any from this forum!!

However, anyone else looking for a solution to this problem, I've shown the formula below;
equation.jpg
C25 is the calculated conductivity at 25°C, Ct is the measured conductivity at t°C, and a is the linear temperature coefficient expressed as a decimal fraction. The linear temperature coefficient is user selectable between 0 and 5% per °C (a = 0.00 to 0.05).

Paul
 
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