126 



USRL TEST STATIONS 



Figure 64. Making impedance measurements using the 

 W lOt 34 impedance bridge, tire 31 A detector, and the 17B 

 oscillator. 



and a 31 A transmission measuring set, is mounted on 

 a rack equipped with casters. See Figure 64. 



The W-10093 Capacitance and Conductance Bridge 

 for measurements at high frequencies was constructed 

 by Leeds and Northrup Company, Inc. in accordance 

 with a design by Bell Telephone Laboratories. The 

 normal frequency range is 50 kc to 5 mc but it may be 

 used as low as 10 kc and as high as 10 mc without 

 serious loss of sensitivity or accuracy. The capacitance 

 range is from 0.0 1 to 1 ,100 ^1 either positive or nega- 

 tive and the range may be extended well beyond 

 11,000 Mxi by means of five plug-in standards. The 

 conductance range is from 0.001 to 1,100 ^mhos and 

 may be extended to 1 1 ,000 /xinhos and further by 

 plug-in standards. Both types of measurement may be 

 extended even further by connecting a known admit- 

 tance in series with the one to be tested. For the nor- 



mal frequency range the accuracy is about 0.25 per 

 cent. 



The General Radio Company Impedance Bridge 

 Model 650A is a direct-reading instrument with a self- 

 contained battery and a 1,000-c oscillator. It gives 

 quick approximations of impedance at 1,000 c or 

 with direct current. It gives d-c resistances from 1 

 ohm to 1 megohm, capacitances from f,000 /r/d to 

 100 /d, and inductances from 1 /xh to 11 h. 



A Leeds and Northrup Company Wheatstone 

 Bridge is used for precise d-c resistance measurements. 



Test Meters 



The meters used at the laboratories are standard 

 ohmmeters and voltmeters with the exception of a 

 special megohmmeter and a 31 A transmission meas- 

 uring set. Several portable Simpson and Weston volt- 

 ohm ammeters are used in the maintenance of the 

 electronic equipment and in making the customary 

 electrical checks on transducers. A number of elec- 

 tronic voltmeters are used for measurements where 

 the test meter must have a high impedance. 



A Ballantine a-c Voltmeter measures rms voltages 

 from 0.001 to 100 volts over a frequency range of 

 about 10 to 150,000 cycles with a general accuracy of 

 2 per cent. When used in conjunction with a decade 

 amplifier, measurements may be made considerably 

 below a millivolt with frequencies from 10 to 100,000 

 c. The use of a special multiplier extends the upper 

 limit to 1,000 volts. 



The Hewlett Packard Vacuum -Tube Voltmeter, 

 Model -fOOA, is used extensively for relative measure- 

 ments of rms voltages between 0.03 and 300 volts over 

 the frequency range 10 c to 1 mc. 



The Measurements Corporation Electronic Volt- 

 meter, Model 62, provides ranges of 1, 3, 10, 30, and 

 100 volts with an accuracy of 2 per cent of the full- 

 scale reading. When used with its associated probe, it 

 allows measurements from 30 c to 150 mc. It should 

 be noted that it reads peak voltages. A specially de- 

 signed vacuum-tube thermocouple voltmeter was 

 constructed by USRL for rms voltages. 



A special Raxuson Electrical Instrument Company 

 Megohmmeter is used primarily for measuring in- 

 sulation resistance at 2,500 volts and covers to 100 

 and to 10,000 reading directly in megohms. 



A Western Electric Company 31A Transmission 

 Measuring Set is used extensively as a null indicator 

 for the various impedance bridges. The high sensitiv- 

 ity and frequency discrimination provide excellent 



