EQUIPMENT AT MOUNTAIN LAKES 



125 



0.5 



1x10"+ 2xlCT* 3x10"+ 4xl0- + 5*I0~* 



TIME (SECONDS) 

 A 



70 



40 



2 3 4 5 10 



FREQUENCY IN KILOCYLES PER SECOND 

 B 



Figure 63. Transient analysis of explosive wave form. 



curve, it may lie assumed that the phase relation is 

 fairly linear. This assumption should be further in- 

 vestigated. However, the phase-frequency character- 

 istic does not affect the amplitude-frequency analysis 

 of the transient but only affects its wave form. 



The frequency analysis of the transient is made 

 from the photographic record by the use of a har- 

 monic analyzer. The USRL was fortunate in having 

 the use of a Henrici Analyzer/'*' 7!l through the coop- 

 eration of the Department of Physics, Case School of 

 Applied Science. This analyzer gives the relative am- 

 plitudes of thirty harmonics. A complete frequency 

 analysis of a transient requires from several hours to 

 several days, depending on the complexity of the 

 transient. The resultant data are then only relative 

 and require supplementary computations for conver- 

 sion to actual units such as pressure and frequency. A 

 sample anal) sis of an explosive wave by this method 

 is shown in Figure 63. The analysis gives the rms pres- 

 sure in db vs 1 dyne per sq cm in a 1-c band as a func- 

 tion of frequency. 



6 - 8 Auxiliary Laboratory Equipment 



Considerable auxiliary equipment is needed in the 

 calibration and maintenance of the measuring sys- 



tems as well as in the calibration ol transducers. For 

 convenience in description the apparatus is divided 

 into six groups: resistance and impedance bridges, 

 test meters, portable signal generators, cathode-ray 

 oscilloscopes, wattmeters, and miscellaneous equip- 

 ment. 



Resistance and Impedance Measuring Bridges 



The laboratories are provided with a number of 

 admittance and impedance bridges suitable for meas- 

 urements over a wide range ol values with the various 

 frequency ranges. 



The Western Electric Company 5A Impedance 

 Bridget is used in the frequency range 1 to 150 kc. It 

 is an admittance bridge of the comparison type, meas- 

 uring impedance in terms of the equivalent parallel 

 resistance and capacitance components. It permits 

 measurements on devices which are electrically bal- 

 anced or unbalanced to ground. It measures parallel 

 resistance components up to 1.100 ohms directly with 

 supplementary computation to 1 megohm. Parallel 

 capacitance (or inductance considered as negative 

 capacitance) may be measured directly up to 0.1 I /A. 

 and above this value by the addition of external ca- 

 pacitance. The bridge is designed for an overall ac- 

 curacy in impedance determinations of ±0.5 per 

 cent, but it has reduced accuracy for extremely high 

 parallel resistive components. It is ordinarily used 

 with a 17B oscillator and a 31 A transmission measur- 

 ing set detector described later in this section. A typi- 

 cal arrangement of these devices can be seen in Figure 

 4. 



The Bell Telephone Laboratories W-10134 Imped- 

 ance Bridge consists essentially of two units, a capac- 

 itance comparison bridge and a Maxwell inductance 

 bridge, thereby obviating the computations necessary 

 to convert parallel values to series values or vice versa. 

 The use of the bridge is limited to electrically unbal- 

 anced instruments and a frequency range of 200 c to 

 150 kc. The comparison bridge measures capacitances 

 from 0.1 mil to 1.11 fd and conductances from 0.01 

 fimho to 1 1 1.100 jumhos. The Maxwell bridge meas- 

 ures inductances from 0. 1 ,Ji to 1 . 1 1 h and resistances 

 from 0.01 ohm to 111,100 ohms. The accuracy of 

 direct bridge readings is approximately ± 1 per cent. 

 Complete operating instructions and descriptive ma- 

 terial are available which give correction factors to 

 obtain a precision of ±0.1 per cent. 



To facilitate impedance measurements at the test- 

 ing area, this bridge, together with a 17B oscillator 



