Help me with ultrasonic and capactive way for soil moisture!

[kamelian_20]

soil mosture

hi all
i try to builed a kind of system to measure the soil moisture. i need a kind of accurate and economical system.amonge my research i found lots of way like TDR , chilled mirror hygrometer , thin films,ultrasonic and capacitive sensing. i need some help for ultrasonic and capacitive way.

regard

 

[ehsanelahimirza]

soil mosture

what kind of help do u need?
if recommendation then i will say to use capacitive devices. most humidity sensors based upon variable capacitance and have good results and even dont require any calibration.

 

[kamelian_20]

Re: soil mosture

i think the capacitance method are easy to implement and also reasonable but i am not sure about the precision and accuracy.
how do you think about it?
i also need some reliable and good circuits for implement this system.
the TDR and some other methods are so complicated and expensive.

 

[FvM]

Re: soil mosture

basically, you should ask: what property you want or you need to know. "Soil moisture" is rather a colloquial term than designating an exact property. In enviromental engineering (don't know about agriculture), water content is mostly defined as percentage of dry material contained in a sample, a gravimetric measure. It can be excactly determined only by drying the sample.

As an approximate value, a capacitive measurement is often used, but it has to be calibrated with similar material. In contrast, vapour pressure respectively dew-point, as measured with the said hygrometer, is a completely different property,
although the two are apparently related.

 

[kamelian_20]

Re: soil mosture

hi all
you know the way you said like taking some samples from the soil we want to measure the water content and trying to dry it and then measure the weight differences is a kind of old method.
today agricultral engineers calculate the soil moisture with lots of very accurate and complex method like TDR, Microwave,frequency domain, and also ultrasonic.
the goal of all this method is just water content of soil.in most new method they measure the dielectric constant of the soil because there is a large differences between the water dielectric constant and other content dielectric constant of the soil.
also i think the capacitance method use this theory but i think it is typically use for air humidity measurment.
i want to know how exactly the ultrasonic and capacitance method work