BS EN IEC 62961:2018 pdf download.Insulating liquids -Test methods for the determination of interfacial tension of insulating liquids - Determination with the ring method.
To obtain exact values for surface or interfacial tension， it is necessary to measure themaximum force on pulling the ring out of the liquid.Because of the great risk of detachment inthe case of the manual apparatus，extremely smooth manipulation is necessary since thevalue obtained immediately prior to detachment of the film is not identical to the maximumvalue. Automatic tensiometers can determine the maximum value electronically and reversethe platform movement promptly prior to detachment of the film. This makes it possible toobtain reliable,accurate time-consistent serial measurements without tearing the film.
5 Apparatus
5.1Tensiometer
The tensiometer shall be designed for a ring and shall consist mainly of two parts:
support for the sample vessel in the form of a small horizontal platform which can be moved up and down;
apparatus for measuring the force exerted on the ring; the uncertainty of measurementshall not exceed ± 10-6 N, which corresponds to a maximum error of ± 0,1 mg weightmeasurement.
Instead of a torsion balance as stated in ASTM D971，a lever balance or an electronicbalance (laboratory,analytical or microbalance) can be used.To obtain higher efficiency andreproducibility, it is recommended to use an automatic tensiometer incorporating a balance,motor driven platform and evaluation unit.
