A prototype for the automation of a pressure pump type Schölander is being developed. Determining the total water potential (TWP) using a pressure pump (Schölander pump) depends on the proper use and training of the operator but this does not ensure the accuracy and precision of the measurements being made. To avoid this problem, we are developing an automatic control and measurement system. The prototype system consists in of automatic controller that controls a valve with differential step pressure control (which allows gradual increases in pressure inside the chamber) and optical sensor (which determine when water runs out of the petiole). With the integration of these components, it is possible to make the measurement automatically and it eliminates the human error in determining the TWP. On the other hand, this prototype allows the standardization of the speed and the increment of the pressure differential on the determination of TWP.