Iskanje po katalogu digitalne knjižnice

Opis: V magistrski nalogi so predstavljeni različni modeli pospešenih testov in klimatskih komor, v katerih se ti izvajajo. Za izvedbo deseturnega pospešenega testiranja preprostega vezja z LED diodo je bil uporabljen standard IEC 60068-2-38. Med testiranjem so se spremljali vpliv temperature in relativne vlažnosti na upornost predupora in LED diodo. Za namene testiranja ročnega mešalnika je bilo izvedeno HALT testiranje, pri katerem se je preverjala pravilnost delovanja glede na podano specifikacijo proizvajalca. Pri tem testu smo se osredotočili na čas delovanja ročnega mešalnika pri polni hitrosti do pojava odpovednih mehanizmov.
Ključne besede: klimatska komora, pospešeno testiranje, temperatura, relativna vlažnost, IEC standard, HASS
Objavljeno v DKUM: 27.03.2025; Ogledov: 0; Prenosov: 13
Celotno besedilo (3,97 MB)

Opis: The magnitude of the relative permittivity of the ferroelectric nematic phase (NF ) has been the subject of lively scientific discussion since the phase was recently discovered. Dielectric spectroscopy measurements (DSMs) give a huge value of relative permittivity, which depends on the cell thickness, but this is argued to result from a misinterpretation of the DSM results. We have conducted DSM using a set of cells differing in thickness of the NF layer, type of electrodes, and presence/absence of nanoscale-thick surface polymer layers. To model the DSM results, cells are presented by an equivalent electric circuit that includes a capacitor due to the NF layer with frequency dependent complex relative permittivity, capacitors due to surface layers, and a resistor describing the limited conductivity of electrodes. DSM results for different cells with the same liquid crystal in the NF phase are semiquantitatively reproduced by the same set of physical parameters if a huge relative permittivity of the NF , which is even orders of magnitude larger than the measured apparent values, is assumed. We show that the capacitance of surface layers should also be considered in cells with no polymer alignment layer on the electrodes.
Ključne besede: liquid crystals, statistical physics
Objavljeno v DKUM: 27.11.2024; Ogledov: 0; Prenosov: 6
Celotno besedilo (669,38 KB)
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Opis: Namen tega projekta je bilo ustvariti vezje, ki bo omogočalo napajanje poljubnega bremena in istočasno merjenje stanja napolnjenosti dveh zaporedno vezanih Li – ionskih baterij, ki breme napajata ter posredovanje podatkov na mobilni telefon preko Bluetooth komunikacije. Izdelano je bilo tiskano vezje, ki vključuje mikrokrmilnik za katerega je bil napisan program, ki omogoča branje napetosti na njegovih vhodih in vse potrebne izračune. Vezje in program sta od začetka delovala kot pričakovano. Vsi potrebni podatki so bili uspešno posredovani na mobilni telefon. Poleg tega je projekt vključeval tudi eksperimentalno določanje kapacitete baterij in pa večkratno analizo praznjenja, katere ugotovitve so služile za izboljšavo programa.
Ključne besede: Li-ionska baterija, stanje napolnjenosti, električni tok, kapaciteta, praznjenje
Objavljeno v DKUM: 07.10.2024; Ogledov: 0; Prenosov: 13
Celotno besedilo (1,52 MB)

Opis: We proposed a method for measuring frequency differences of the order of a few Hz with an experimental error lower than 0.0001% by using two 4 MHz quartz oscillators, the frequencies of which are very close (a few 10 Hz difference) due to the dual mode operation (differential mode with two temperature-compensated signal frequencies or a mode with one signal and one reference frequency). We compared the existing methods for measuring frequency differences with the new method which is based on counting the number of transitions through zero within one beat period of the signal. The measuring procedure requires equal experimental conditions (temperature, pressure, humidity, parasitic impedances etc.) for both quartz oscillators. To ensure equal resonant conditions for oscillation two quartz crystals are needed, which form a temperature pair. The frequencies and resonant conditions of both oscillators must be almost equal, which is achieved by an external inductance or capacitance. In such a way, we minimized all the external effects and ensured highly stable oscillations and high sensitivity of the differential sensors. The counter detects one beat period by an external gate signal former. By using the method of counting transitions through zero within one beat period, we reduced the measuring error by three orders of magnitude, compared to the existing methods.
Ključne besede: small frequency difference measurement, temperature-compensated quartz sensors, differential sensors, quartz oscillators, transitions-through-zero method
Objavljeno v DKUM: 26.03.2024; Ogledov: 357; Prenosov: 246
Celotno besedilo (4,21 MB)
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Opis: Namen projekta, kot že samo ime pove, je narediti sistem merjenja napolnjenosti neke litij-ion-ske baterije z uporabo mobilnega telefona. Skratka se ima električno vezje, katerega ključni elementi so porabnik, baterija in bluetooth modul – v tem primeru BM70, ter mobilni telefon, kamor se preko bluetooth komunikacije iz čipa BM70 pošiljajo podatki o električnih veličinah vezja in tam tudi obdelujejo v programu mobilne aplikacije. Ob poznanih karakteristikah uporabljene baterije, aplikacija tudi izpisuje napolnjenost baterije oziroma preostanek energije v realnem času, ko je porabnik aktiven.
Ključne besede: baterija, bluetooth, napolnjenost, poraba
Objavljeno v DKUM: 05.10.2023; Ogledov: 329; Prenosov: 52
Celotno besedilo (3,79 MB)