DRAWING TABLES DRIVEN BY ELECTRONIC SERVOS, ETC. 
II 
corresponds to an angle of less than 360 0 ; in effect if under these conditions we 
should have, for instance, an interruption in the network current, as soon as the cur 
rent is restored, the synchro-receiver rotor starts rotating till it reaches the coin 
cidence position. 
Otherwise the sensitivity of the synchro-transmission would be very low and 
consequently the transmission accuracy very limited : in fact we would lose as 
many whole rotations as are those which have taken place during the voltage in 
terruption. 
In order to avoid this, we use two synchro-transmitters and two synchro-re 
ceivers, coupled as described hereafter. 
The synchro-transmitter receiving the carriage movement (fast-synchro-tran 
smitter) is coupled with a second synchro-transmitter (.slow-synchro-transmitter) 
(fig. 8) by means of a mechanical coupling reducing the latter speed by 75 times. 
sincro-trasmettitore 
veloce 
sincro-trasmettitore 
lento 
Fig. 8 - Mechanical coupling of synchro-transmitters 
Collegamento meccanico dei sincro-trasmettitori 
By means of this device the slow-synchro provides the required conditions 
for givin a univocal correspondence for displacements up to 75 rotations of the 
fast-synchro, i. e. it ensures the univocal correspondence between the transmitted 
and the plotted position ; the fast-synchro (which does not provide the univocal 
condition, ensured by the slow-synchro) allows on the other hand a high sensitivity 
near the coincidence position (i. e. for relatively low error values) hence a high pre 
cision of transmission. 
An identical mechanical coupling is set up between the aforementioned synchri- 
receiver (fast-synchro-receiver) and a second synchro-receiver (slow-synchro- 
receiver) (fig. 9). 
The connection between transmitters and receivers is shown in fig. 10. 
It is now necessary to introduce a special device, called synchronizer, between the 
synchro-receiver output and the synchro-amplifier input, to transfer to the servo- 
amplifier input the voltage-error of the slow-synchro, when the error is of a high 
value (such as may create for the fast-synchro the univocity problem of the po 
sition transmitted), or the voltage-error of the fast-synchro for small values of 
the voltage itself (and therefore under the limit below which the univocity of