The principal components of the tensiometer are shown in Figure 3.1. The porous ceramic tip is a key component of the instrument. This should be correctly inserted in the soil. After the tensiometer has been properly installed, the water in the plastic tube comes in contact with the moisture in the soil pores, flowing in both directions until the equilibrium is reached. It is assumed that the soil moisture tension is same as indicated by the vacuum gage of the tensiometer 
As the soil continues to loose moisture due to water use by the roots, the tension (or the suction) of soil is increased. This tension is measured with a vacuum gage of the tensiometer (Figure 3.1). When the soil is again wetted by the rainfall or irrigation, the tension falls since the soil water flows through the pores of the ceramic tip. The tensiometer readings can be related to water available to plants but cannot be used to determine the amount of water in the soil. However, a soil moisture curve can help to identify the status of soil moisture if one knows the soil tension.