摘要:

Existing types of flame-heated ovens have been examined and described because the successful application of electric baking ovens involves a thorough understanding of the principles of bread-baking and cake-baking.Tests for determining the uniformity of temperature in flame types of ovens are illustrated and summarized, mainly because the electric oven lends itself to greater uniformity of temperature by grading and locating the elements.Constructional details of electric ovens are dealt with as an indication of the suitability of each type for particular locations. Portable and brick-built oven construction is illustrated and explained. British, American and Continental ovens are surveyed.A glossary of terms peculiar to the baking trade has been compiled by the author as no published definitions of the terms have hitherto been available.Operation costs are shown, including maximum-demand averages from more than 100 installations.The demand for the abolition of night baking has a very important bearing on the most suitable type of electric baking oven construction, and the brick-built oven with high heat-storage capacity and high thermal efficiency deserves careful consideration. These ovens are heated during “off peak” periods only.

DOI:10.1049/jiee-1.1928.0056

出版商:IEE    

年代:1928

数据来源: IET

DOI:10.1049/jiee-1.1928.0061

出版商:IEE    

年代:1928

数据来源: IET

摘要:

This investigation was carried out for the purpose of finding whether the assumption usually made regarding the distribution of current in an antenna was a sufficiently close approximation to the conditions that obtain in practice.The current distribution of a straight, vertical antenna was found experimentally by placing ammeters at various points along the antenna and reading them by means of a telescope. In order that the effect of the ammeters might be calculated, the antenna was constructed in the form of a cage with the ammeters inside. Thus the capacity effects of the ammeters were eliminated. The self-inductance of the ammeters was measured and a correction for it was applied to the theoretical curves.The comparison of the experimental and theoretical curves, calculated on the usual simple theory that the current distribution is sinusoidal, showed remarkably good agreement over the whole range of wave-lengths used (15 m to 800 m). The highest frequency was nearly three times the natural frequency of the antenna.According to the simple theory, the natural wave-length of a simple antenna is 4 times its length. More rigorous mathematics led Macdonald. to put the figure in some cases as high as 5 times its length, and this figure is often quoted in textbooks. This was reduced to 4.2 times by Abraham and Föppl. The experimental results of this paper agree with the latter figure.The effect of a change in diameter of the wire at a point in an antenna was investigated and found to agree with theory. Various shapes of antenn∟ were also tested, including the common inverted “L” and “T” antenna∟. The effect on the current distribution of a conductor placed near the antenna was also examined with the conductor insulated, earthed and tuned, and was found to be negligible.A theoretical analysis, which is unfortunately very laborious to apply, agreed with the experimental results obtained.

DOI:10.1049/jiee-1.1928.0062

出版商:IEE    

年代:1928

数据来源: IET

摘要:

An expression is obtained for that part of the distortion introduced by line irregularity; a similar disturbance is caused in the variation of the sending-end impedance with frequency. The nature of the distortion is examined, and it is shown that the effect of an irregularity is greater the nearer it is to the transmitting end; it tends to damp out with an increase in the length of the line, and at a repeater the line effectively recommences. Distortion due to differential frequency attenuation, however, increases with the length of the line; the interposition of repeaters has no effect. To reduce distortion due to irregularity it is essential to eliminate as far as possible irregularities near the transmitting end (including in this term portions of the line immediately beyond a repeater). For the transmission of music it is desirable to use separate lines and eliminate repeaters, or reduce their number to a minimum.

DOI:10.1049/jiee-1.1928.0063

出版商:IEE    

年代:1928

数据来源: IET

摘要:

A method is given of determining an impedance which shall balance a line over a wide range of frequencies (rendered necessary by the use of lines for the transmission of music). No difficulty is found in balancing the line almost exactly. In cases where line balancing is not essential, the possibility of counteracting the distortion caused by differential frequency attenuation, by deliberately making the line reflective, is considered. It is shown that the complete accomplishment of this is not a practical possibility, but that the transmissible range of the line can be extended by about one octave for the same limit of distortion.

DOI:10.1049/jiee-1.1928.0064

出版商:IEE    

年代:1928

数据来源: IET

摘要:

The method introduced in 1923 by E. Biffi is discussed. Formulae are obtained for ratio and phase angle and for the galvanometer current. Biffi's formula for the ratio of current transformation is made more precise by the introduction of a term which takes account of the effect of the condenser current upon the ratio. This correction is necessary in accurate work. The application of the method to comparative tests is dealt with.

DOI:10.1049/jiee-1.1928.0067

出版商:IEE    

年代:1928

数据来源: IET