12 
CARLO TROMBETTI 
Alla trasmissione X (Y) 
del tavolo 
Fig. 9 - Mechanical coupling of synchro-receivers and motor-tachymeter 
Collegamento meccanico dei sincro-ricevitori e del mototachimetro 
the transmission problem does not arise for the fast-synchro). Thus inside the coin 
cidence position, which is the interesting one as far as the transmission precision is 
concerned, the system sensitivity is that corresponding to the fast-synchro, i. e. 75 
times more than that which might be obtained with one synchro only. 
The principle on which the synchronizer operates is shown schematically in 
fig. ii. It consists essentially of two systems of biased diodes ,the one inserted in 
parallel to the voltage error of the fast-synchro, the other in series to the voltage- 
error of the slow-synchro. The biased system offers a very high resistance when 
the applied voltage does not exceed the threshold value, and, on the contrary, a 
very low resistance when such value has been exceeded ; it thus behaves more or 
less as an open switch which shuts when the applied voltage exceeds the threshold 
value. By suitably setting the voltage thresholds, in correspondence to the values 
where the slow-fast commutation and vice-versa should take place, we automati 
cally obtain the desired commutation. In effect, below the said limit both thre 
shold systems behave as open switches and the voltage transferred is that of the 
fast-synchro; above the commutation limit both diode systems close up and the 
slow-synchro voltage is applied directly to the input of the servo-amplifier, whereas 
the fast-synchro voltage is practically short-circuited with regard to the servo- 
amplifier input, and thus not in a position to affect it. 
4. The o 30 M drawing table. 
The drawing table realizing the diagram of fig. 10, i. e. the most perfect scheme, 
is the 0 30 M built by Officine Galileo, which we shall now describe.