Målet med examensarbetet har varit att ta fram teoretiskt underlag och en beräkningsmodell. Detta ska beskriva hur kabeltyp, kabellängd, kabelarea samt effektfaktor påverkar spänningsfallet över ett 400 Hz ledningssystem. Mätningar har utförts på två olika kablar som används i det aktuella systemet. En av kablarna var symm­et­riskt uppbyggd med 7 ledare, där respektive fas bestod av två ledare förskjutna 180° från varandra runt nolledaren. För att åstadkomma 115/200V 400 Hz, användes en 90 kVA frekvensomformare. Belastningen som användes var en resistiv, induktiv samt en kapacitiv belastning. Med den resistiva belastningen justerades effekten för att ställa in den effektfaktor som önskades under mätningarna. Detta var inte möjligt med den induktiva eller den kapacitiva belastningen, då de inte kunde regleras steglöst.   Beräkningsmodellen jämfördes sedan med mätningarna av spänningsfallet. Den visade sig ge en bra uppskattning av de uppmätta värdena för att kunna användas i Saabs fortsatta arbete. Vidare ges förslag på hur de distorsioner som uppstår, i samband med komplexa laster, kan minskas. Detta för att klara de standardiserade mått på elkvaliteten som ställs i de gällande standarderna MIL-STD-704E och ISO 6858-1982 (E). Beräkningsmodellen och dess beräkningar presenteras dock inte i denna rapport, då det av Saab AB är sekretessbelagda. / The goal with this bachelor thesis has been to present theoretical material and a calculation model. This is to be used to explain how cable type, cable length, cable area affects the voltage drop in a 400 Hz power system. Measurements have been made on two different cables that are being used in the current system. One of the cables was built symmetrically built with 7-conduktors, where each phase consisted of two conductors shifted 180° from each other around the neutral conductor. To establish the system voltage 115/200 V 400 Hz, a 90 kVA frequency converter was used. The load that was used under the measurements was a resistive, inductive and a capacitive load-equipment. With the resistive load active power is adjusted to obtain the proper power factor for different measurements. This was not an option with the inductive or the capacitive load-equipment since they could not be regulated with a rheostat as the resistive load. The calculation model was compared with the measured results of the voltage drop. It was proven that it approximated the voltage drop good enough to be used in Saabs future work. Furthermore, suggestions are made of how to minimize the distortions that are developed by complex loads, to clear the demands on power quality presented by the standards MIL-STD-704E and ISO 6858-1982 (E).

Background: Pure-tone, air-conduction audiograms notched at 4000 Hz have long been considered the signature configuration for noise-induced hearing loss even though there is an extensive literature that does not mesh with this simple explanation. There are many reports of notched audiograms from individuals with no history of noise exposure and, conversely, reports of audiograms with no notches from individuals with a history of noise exposure. Recent reports increasingly suggest that unilateral 4000 Hz notches are common. The prevalence of notched audiograms at 4000 Hz is dependent on the definition of the notch and the population under study. Purpose: To examine the prevalence and characteristics of audiograms that are notched at 4000 Hz. Research Design: Retrospective, descriptive. Study Sample: The participants were 3430 veterans evaluated in the Audiology Clinic at the VA Medical Center, Mountain Home, Tennessee. The mean age was 62.3 yr. Data Collection and Analyses: The data were collected in the course of a 60 min, routine audiological evaluation. In addition to pure-tone audiometry, a history, otoscopy, speech audiometry in quiet and in noise, and aural-acoustic immittance measures were included in the clinic protocol but were not evaluated in this report. A notch was defined when the 4000 Hz threshold minus the 2000 Hz threshold and the 4000 Hz threshold minus the 8000 Hz threshold both were ≥10 dB. Results: Overall the mean LE (left ear) thresholds at 2000, 3000, and 4000 Hz were at hearing levels 2-3 dB higher than the hearing levels for the corresponding mean RE (right ear) thresholds; the differences were significant. A notched audiogram was observed in 40.6% of the participants in at least one ear with 15.4% having bilateral notches, 28.8% LE notches, and 27.1% RE notches. Unilateral 4000 Hz notches were almost twice as prevalent as bilateral 4000 Hz notches. Viewed as a function of age, notched audiograms were most common (∼35% of the participants) in the 40 and 50 yr groups with a diminishing prevalence in the 60-80 yr groups. The mean notch depth at 4000 Hz was consistently 20-26 dB across the seven age groups. In comparison to the thresholds of the audiograms that were not notched, the thresholds of the audiograms with 4000 Hz notches (1) at 250-2000 Hz were at hearing levels 2-3 dB lower, (2) at 3000 and 4000 Hz were at hearing levels 8-17 dB higher, and (3) at 8000 Hz were at hearing levels 3-4 dB lower; the threshold differences were significant at all frequencies for both ears. Conclusions: The data suggest that unilateral, 4000 Hz notched audiograms are as common or more common than bilateral notched audiograms and that unilateral notched audiograms are equally common for the LE and RE. The prevalence and characteristics of 4000 Hz notched audiograms in this veteran sample are similar to those observed in the population as a whole.

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This study aims to investigate the evoked and the induced activity in 40 Hz auditory responses. The 40 Hz activity, also called Pb or P50 or P1 component, has a latency of 50ms and belongs to the category of MLRs (Middle latency responses), which occur right after Auditory Brainstem Responses (ABRs) between 15 and 80ms. Its importance is related to possible clinical applications such as anesthesia, schizophrenia and auditory development. In addition to this, evoked and induced activities at 40 Hz might play an important role in cognitive processing. Trains of right ear rarefaction clicks at the mean rate of 39.1 Hz, intensity of 50dB and duration of 100 were used to elicit the above mentioned activities. Three different sequences have been used: steady state, low jittered and medium jittered. Low jittered sequence has been the main sequence used to study the 40 Hz activity. The advantage of using this sequence is the fact that a deconvolution analysis can be performed and also the fact that it does not differ too much from the standard 40Hz steady-state sequence and this means that a resonance at 40 Hz can still be obtained. Ten healthy subjects (8 males and 2 females; ages ranging from 25 to 47), with no history of audiological or neurological hearing impairment were recorded. Informed consent was signed according to approved IRB protocols. All recordings were done in a sound-proof chamber (Acoustic Systems, Inc.) with subjects lying on a bed comfortably. The subjects were not asked to perform any tasks, but just to passively listen to the acoustical stimuli. Evoked and induced activities were recorded in response to the above mentioned acoustic stimuli. The deconvolution analysis showed that the peak of activity occurs around 152ms. Wavelets analysis has confirmed this observation and has also unveiled and induced activity in the low beta range. This induced activity seems to be strictly related to the evoked activity, as it seems to occur around 390ms, which corresponds to the situation where the 40 Hz evoked activity enters a steady state condition, which lasts until the last acoustic stimulus has been applied. The latter observation is again in accordance with the literature, where it is reported that the 40Hz evoked activity could reflect the initial coactivation of neural assemblies representing specific stimulus features. A change in such stimulus features could be reflected as induced oscillations occurring in the middle beta range (16-22 Hz).