. Basic methods for the calibration of sonar equipment. 128 USRL TEST STATIONS '"SLx::^^ OUTPUT. 1 -^/\/V—T—° 0' :E Qrn Figure 66. Circuit schematic of thermocouple wattmeter; circuit arrangements are shown for: (A) power measure- ment. (B) current measuicment, (C) vohage measurement. dances from 10 to 'iOO and has power scales of 100, 500, and 1,000 watts. The indicated and actual scale factors agree within per cent from 0 to 100 kc. Operation outside the impedance limits will not only affect the accuracy and overload the thermo- couples but even may destroy them. While the th
. Basic methods for the calibration of sonar equipment. 128 USRL TEST STATIONS '"SLx::^^ OUTPUT. 1 -^/\/V—T—° 0' :E Qrn Figure 66. Circuit schematic of thermocouple wattmeter; circuit arrangements are shown for: (A) power measure- ment. (B) current measuicment, (C) vohage measurement. dances from 10 to 'iOO and has power scales of 100, 500, and 1,000 watts. The indicated and actual scale factors agree within per cent from 0 to 100 kc. Operation outside the impedance limits will not only affect the accuracy and overload the thermo- couples but even may destroy them. While the thermocou])le wattmeter is direct-read- ing and fairly accmatc, the time required to reach temperature ecjuilibriiim delays the readings so that point b\ point mcasinements are required. The pos- sible destruction of the thermocouples from sudden changes in load impedance and the limited impe- dance range for any one power scale are distinct dis- advantages. The recording wattmeter was designed to overcome these difficulties. Recording Wattmeter.''''' In measurements with the recording wattmeter, two signals designated 2 and A are obtained and recorded. 7 he signal 2 is obtained by adding a signal which is >i times the current i to one which is in times the \oltagc r. The signal A is the difference between ;/; and ?ne. It can be shown that A- imn ei cos 6 = Power, (2) where 6 is the phase angle between the current and \()ltage. The 2 and A signals are recorded on the in- termediate-frequency systems in the usual manner. The measurement of total power is correct only for sinusoidal waves. For portable use. separate ampli- fiers and meters may be used in place of the recorders. Figures 67 and 68 show the connections used in obtaining the 2 and A terms for unbalanced and bal- anced circuits. In the actual circuit for an unbalanced load, a coil and pad replace the R^ resistors in turn to obtain the 2 or A signal. The voltage component is obtained by short-circuiting R., and t
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