A prototype permittivity measuring device was fabricated at the Advanced Textiles and Composites Laboratory of Philadelphia University to apply the Advanced Permittivity Testing Method to several woven fabrics for the purpose of ascertaining the reliability and reproducibility of this method.

The commercial linear actuator shown in Figure 3.1 moves the two pistons simultaneously through a linkage arrangement. By removing the cylinder securing bolts  of the permittivity measuring device, the specimen holder can be slipped between them.

A test using the Advanced Permittivity Testing Method was conducted by first filling both cylinders with the fluid to be used, in this case plain water.  The enclosed water was slightly pressurized by advancing one of the piston rods. That pressure was maintained indicated that the cylinders were water tight, including their piston-ring seals.

Piston travel was was then initiated. Generally, ten cycles were observed. Figure 3.2 illustrates six such Advanced Permittivity Testing Method cycles, showing the gratifying reproducibility. The red curve plots the output signal from one of the pressure transducers and the blue curve from the other transducer. The red and blue vertical scale readings are converted directly into DP using the pressure gauge constant which relates voltage to pressure. Significantly, only voltage differences are required, so voltage calibration is not needed. Of course, the upstream transducer becomes the downstream transducer and vice versa when the piston travel direction is reversed.

The chart constant converts the chart speed to piston speed from which the fluid flow rate is calculated. From this information and the piston travel speed the permittivity of the specimen fabric can be readily and rapidly determined.

Considering its one-of-a-kind status, the prototype testing device operated quite successfully. Because the cylinder walls were not honed, the piston rings apparently exhibited slip-stick motion, resulting in the serrated pressure peaks. The linkage mechanism between the actuator and the piston rods needs improvement, or, better yet, elimination, as shown in Figures 4.7 and 5.6, by integrating the actuator and cylinders into a single unit.

Figure 3.3 shows the results of the laboratory model of the Advanced Permittivity Testing Method flow versus pressure difference data for a plain-weave polyester fabric.

The linear relationship between pressure difference and the flow rate is indicative of laminar fluid flow through the plain weave.  Considering that the permittivity measuring device is a prototype and therefore far from optimized, the close grouping of the data points at each measured piston speed indicates good reproducibility.

In regard to unit convention the pressure difference and the flow velocity can be displayed in many suitable units. For pressure difference the display units might be mm Hg, psi, bars, Pa, dynes/cm² or others. For fluid flow rate per unit area of fabric the display units might be ml/cm²-min, cm/min, in³/in²-min or others. According to Eqs. 3 or 4, the viscosity must be in appropriate units to determine the permittivity from these pressure and velocity readings.