Force Tensiometer measures the moistening of an immersed ring or plate body with respect to the related tensile force. The measurement of surface and interfacial tension is carried out with the Du-Noüy ring or the Wilhelmy method. The software-supported Force Tensiometer Sigma 200 automatically starts the surface and interfacial tension after pressing a button. As a standalone device the tensiometer is equipped with a motorized table for the sample vessel. The Du-Noüy ring moves into the medium to be measured. Then the motor moves the sample table slowly downwards. The forces acting on the ring or plate lamella can be read on the display. Analysis of the interfacial tension of oil versus water using the ring method. The analysis of the interfacial tension between insulating oil and water provides an early warning of the oil aging process. Refer to ASTM D971-99 2012.