Dielectrometry Measurements of Moisture Diffusion and Temperature Dynamics in Oil Impregnated Paper Insulated Electric Power Cables
Paper insulated lead covered (PILC) cables provide the backbone of underground power distribution in the United States and other parts of the world. Efficient replacement of aged PILC is a looming challenge for the utility industry. Interdigital dielectrometry sensors that measure the dielectric properties of PILC cable are presented. Such sensors may be used to perform low cost health assessment of excavated cable samples. An overview of the theoretical groundwork is presented along with steady state and transient experimental results.
Dielectrometry measurements of moisture dynamics in oil-impregnated pressboard
The dielectric spectrum of pressboard, (i.e. its complex permittivity as a function of frequency), is related to its moisture content and to its temperature. Consequently it is possible to use dielectrometry measurements to measure a pressboard sample's moisture content. The complex permittivity of pressboard is measured in two different ways. The first method places the sample between two parallel metal plates, in effect creating a lossy lumped capacitor, whose complex impedance can easily be measured. The complex permittivity thus calculated is effectively averaged across the sample's bulk. The other method involves interdigitated electrodes, applied only to one surface of the sample. Since the electric field's depth of penetration is dependent on the spatial wavelength of the electrodes, different sensors can obtain information from different depths in the material, making it possible to measure spatial distributions of the dielectric properties. This can allow the study of the diffusion of water in pressboard.<<ETX>>
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%