The spring tongues are placed in line with each other, edge to edge, with a sufficient space between them to avoid con tact. They are also hardened and tempered so as to readily return to their normal position after pressure on them is re leased. To the lower end of these tongues a series of resist ances, Ti, are secured, while their upper ends are provided with Ida L inn m contacts.
• Supported kom each holder by two spring strips, which are insulated, is a brass contact bar, 11, having its side next to the steel tongues and arranged at an angle thereto. These two eon tact bars are each provided with a platiumn wire placed opposite the platinum contacts of the spring tongues, and by reason of their spring, supports can be brought in contact with the tongues, each tongue making contact independently of the rest.
The stylus rod, (I, is screwed into the base, and its spring at the lower end allows of a free movement of the upper end in any direction. A pressure block, P, as shown, is secured to the stylus rod. TwO adjustable pressure heads are screwed into this block, and held tightly bylock nuts in whatever position adjusted.
tAchen the stylus is in its normal position, the pressure heads are so adjusted that contact is made with the projection on the contact bar, and the contact bar with the first spring tongue, whereby any lost motion is prevented. When the stylus is operated. the contact bar is pressed against the tongues, making contact with a greater or less number, according to the extent of movement of the stylus, thus cutting in, or out, the resistances required to reg ulate the movement of the receiving pen. The resistances are arranged to avoid any break of circuit or oxidation at the contact points.
There are two series of resistances employed for each set of tongues, and both connected to them in the manner shown in Fig. 23. One, a, a', a', etc., is arranged in parallel are ; the other, b, 6', etc.. in series ; and both combined. The resistance of a', measured in ohms, is the same resistance as b. The resistance of a, is less than the resistance of al, but is the same resistance as and so on ; the resistance continuing to decrease from a maximum resistance arranged farthest from the receiver, to a minimum resistance ; the last tongue to make contact with the contact bar controlling the lowest resistance.
The operation is as follows : When the tongues are out of contact with the contact bar, the current circulates in every branch, being, of course, proportional to the resistance. 'When, through the movement of the stylus, the con tact bar touches tongue No. 2, the resistance, a', is placed in parallel are with resistance, a, while the resistance, b, of resistance equal to a', is practically electricall y cut out. The resistance, 5, therefore, prevents an open circuit in a' when contact 2 breaks contact with the contact bar, bal ancing the resistance. a'. In other words, the resistance, b, offers another and equivalent passage for the current the moment at is separated from a, and so on throughout the remainder of the arrangement of resistances.
This transmitter has been used in commercial work with heavy battery for months, and has never required touching. It has been tried in every style of work expected of the system, and been found reliable.
Twelve contacts give all the variation required for any length of line. A parabolic curve (Fig. 24) describes the curve of resistances, and the same curve is used for all lines. The current used varies from a minimum of to a maximum of '03 of an ampere.
The receiver is shown in Fig. 25. The only adjusting screws about the apparatus are one for each magnet, and these raise or lower the cores to or from the armature, when being adjusted to the line. The double armature, magnetically connected, and the float employed to remove the tremor of the armature rod, are retained. There is an armature (not shown) under the cores of the magnets, which releases the paper-moving mechanism. Under the top plate of the transmitter are contacts which automati cally cut out the transmitter when the stylus rod is released, and also a contact for call ing up when placed in an exchange system..