Measurement Data Types
Automatic analysis measurements include a variety of different data, some of which are simply to judge image quality. The following lists include what can, in principle, be measured. Defects in the image, however, may prevent certain quantities from being measured, in which case there is no entry in the Results box.
Not all parameters are necessarily measured on all systems or in all software versions. The following is a compilation of all combinations.
Image Parameters, Always Measured
Contrast. The overall black to white range of gray scale values found in the image.
Sharpness. Relative focus value, as max gradient of gray scale from one pixel to next.
Black Peak. Blackest gray scale value in image. 0=max black, 255=max white.
White Peak. Whitest gray scale value in image.
Edge Threshold. The gray scale value that defines a liquid edge.
Tip Width. Width or diameter of dispense tip, in mm, measured at the top of the image.
Wetted Tip Width. Width or diameter of dispense tip, in mm, measured at the liquid-solid interface of the drop (i.e., the bottom of the tip).
Contact Angle Parameters
Angle. Average of left and right contact angles, in degrees.
Angle Left. Left side contact angle.
Angle Right. Right side contact angle.
Wet. Average of left and right side wetting tensions. Wetting tension is the cosine of the angle multiplied by the interfacial tension of the liquid. Measured in user-chosen units, e.g., mN/m.
Wet Left. Left side wetting tension.
Wet Right. Right side wetting tension.
Tilt Angle. Apparent tilt away from horizontal of the liquid-solid interfacial line, in degrees.
Base. Diameter of the liquid-solid interfacial circle, or length of the baseline, in mm.
Base Area. Liquid-solid interfacial area, in mm squared.
High = Height. Length of the perpendicular from the drop's apex to the baseline, in mm.
Volume = Sessile Volume. Liquid volume of the sessile drop, in microliters.
Sessile Area. Surface area of the liquid-vapor surface of the sessile drop, in mm squared.
Distance. Length of line, in mm, of user-clicked line on image.
Interfacial Tension Parameters
Surface Tension = Interfacial Tension = IFT. Interfacial tension of liquid, in user-selected units (e.g., mN/m).
Pendant Volume. Volume of the pendant drop, in microliters.
Pendant Area. Surface area of the liquid-vapor interface for the pendant drop.
Maximum Diameter. 2 x radius of curvature. Principally used with magnification calibration standards.
LY b. Laplace-Young "b" factor = radius of curvature at apex of drop, in mm.
LY Beta. Laplace-Young "beta" factor, a dimensionless value, negative for pendant drops and positive for sessile drops.
LY Error. Average RMS error, in mm, for fit between actual drop profile and ideal Laplace-Young profile.
Apex X. Location of X coordinate of the apex of drop in image, measured in mm from the upper left corner.
Apex Y. Location of Y coordinate of the apex of drop in image, measured in mm from the upper left corner.
Dilational StressThese parameters are defined in standard texts on interfacial rheology. They are determined through Fourier analysis of the time history of the interfacial area and tension. The reported values are
Dilational Modulus G.
Modulus G Angle.
Elastic Modulus G'.
Loss Modulus G'.
Differential of Tension.
Differential of Area.
Pressure. Liquid pressure, in Pa.
Temperature. Air temperature, in C.
RH. Relative humidity in air, in %.