ASTM D6181 – Standard Test Method for Measurement of Turbidity in Mineral Insulating Oil of Petroleum Origin (Withdrawn 2012)
Significance and Use
This test method uses a ratio turbidimetric optical system to measure the turbidity of insulating oils relative to turbidity standards. Cloudiness or turbidity is attributed to matter whose diameter is approximately 20 % of the wavelength of the incident light. Increasing turbidity signifies increasing transformer fluid contamination, either from external sources or internal chemical reactions (such as oxidation) that produce fine particulate matter. Other turbidity sources, such as water droplets or gas bubbles, are not of interest in this evaluation of insulating oils. The elimination of these interferences is described in 6.2 and 6.6. This test method quantifies changes which may not be apparent to the unaided human eye.
1.1 This test method covers the laboratory procedure that ascertains the quantity of suspensions in insulating oils of petroleum origin using a nephelometric measurement technique to determine the fluid’s turbidity. This test method is designed to reveal changes that may occur to these oils.
1.2 This test method is applicable for turbidities in the range of 0.1 to 500 Nephelometric Turbidity Units (NTU).
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.