IEC 61868 Mineral insulating oils - Determination of kinematic viscosity at very low temperatures
1 Scope
This International Standard specifies a procedure for the determination of the kinematic viscosity of mineral insulating oils, both transparent and opaque, at very low temperatures, after a cold soaking period of at least 20 h, by measuring the time for a volume of liquid to flow under gravity through a calibrated glass capillary viscometer.
It is applicable at all temperatures to both Newtonian and non-Newtonian liquids having viscosities of up to 20 000 mm2 x s(-1). It is particularly suitable for the measurement of the kinematic viscosity of liquids for use in cold climates, at very low temperatures (-40 °C) or at temperatures between the cloud and pour-point temperatures (typically -20 °C) where some liquids may develop unexpectedly high viscosities under cold soak conditions.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All normative documents are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 3104:1994, Petroleum products - Transparent and opaque liquids - Determination of kinematic viscosity and calculation of dynamic viscosity
ISO 3105:1994, Glass capillary kinematic viscometers - Specification and operating instructions
3 Definitions
For the purpose of this International Standard, the following definitions apply:
3.1 kinematic viscosity
the ratio between the viscosity and the density of the liquid. It is a measure of the resistance to flow of a liquid under gravity
NOTE - In the SI, the unit of kinematic viscosity is the square metre per second (m2 x s(-1)).
3.2 newtonian liquid
a liquid having a viscosity that is independent of the shear stress or shear rate. If the ratio of shear stress to shear rate is not constant, the liquid is non-Newtonian
4 Principle
The time is measured, in seconds, for a fixed volume of liquid to flow under gravity through the capillary of a calibrated viscometer under a reproducible driving head and at a closely controlled temperature. The kinematic viscosity is the product of the measured flow time and the calibration constant of the viscometer derived by direct calibration with a certified reference oil according to ISO 3104.
