M. P. Fodch 109 
j He EH 
SSE arent 
HH rt fait 
15 : # if 
3 
i see eee Seissetizs 
fs Ht sf 
f setae 
20 z 
Ht st 
ee 
a ae X 
= 25 FE i Ht SST Hees : 
oO =. 
= z 
oO +} + 
5 See ees 
3 i # 
ce SE it gatas: 
© 30 a 33 zt 
& = : 
£ oa tesa 
ner 
35 3 is es 
tps + iby i 
zt i 2 : Ba SHIH: f + z eee 
ette: te ft ite ee = sas 
Ht + 3 it +H 
0 5 10 15 20 25 30 35 40 
Fréquence en kHz 
Fig. 6.6. Damping value of the tank lining. 
The tank, shown in Fig. 6.7, is fitted with two movable and rotatable vertical 
shafts, with weight-handling capacities of 150 and 300 kg, rotated by a servomotor 
designed to give a bearing accuracy of 0.10°. 
Because the transducers to be calibrated were of different shapes, a special 
device for fixing them on the shafts hadto be provided for each transducer. Some 
of these devices, shown in Fig. 6.8, are designed in such a way as to permit the 
rotation of the transducer using different rotating axes in order to measure the 
directivity in several planes. 
The electronic instrumentation of this test tank is of an all-purpose design 
allowing complete measurements of transducers, i.e., impedance, response, and 
directivity. 
6.2.1. Impedance Measurement 
An automatic recorder for complex inpedances, the SEXTA4912, is provided 
for measuring and recording the value of transducer impedances as a function of 
frequency. This instrument is of the continuously recording type and has an 
accuracy of +5%. The impedance—frequency plot is displayed on a CRT screen 
in the frequency range 5 to 500 kcps in two bands. Positive and negative re- 
actances from 5 to 10,000 ohms can be measured with this set, and the trans- 
ducer can bé biased by a direct current during this measurement. An additional 
device permits observation onthe CRT ofthe parallel reactances and resistances. 
The remanence of the tube is long enoughto allow the plotting of Kennelly curves. 
This device may very conveniently be used for matching transformers with 
transducers by observing the impedance value when the tuning is completed. 
