Thermocouple psychrometers measure the water potential and its components by determining the vapour pressure in a sealed atmosphere in equilibrium with the sample containing liquid water. The liquid does not need to be continuous, making the method more versatile than others requiring liquid continuity. The sample is enclosed in a small, air-tight chamber and allowed to equilibrate. A thermocouple in the chamber above the sample determines the vapour pressure in the atmosphere and thus in the sample (Boyer, 1995).
