We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
DRIVES 615
The bias of V1! and V-2 rectifiers controls the space current through those tubes, and that space current controls the saturation of the core of the rotor loading coil, L-2. The saturation of the core of L-2 determines the impedance of that coil, and the impedance of L-2 governs the amount of work the rotor must do in turning over, and hence its speed of rotation.
We must now look to see what the 720-cycle current generated in the stationary armature docs to the grid bias of V-4.
Wheatstone Bridge Circuit
The 720-cycle output of the armature is given two parallel paths through which to complete its circuit. One is the primary of T-3, which is divided at its center into two halves. The other path consists of the retard coil L-l and its built-in condenser, plus the resistors R-13, R-14 and R-ll. The resistors constitute the lower half of that path, and the coil with its condenser the upper half. The double primary of transformer T-2 bridges across between these two paths. This arrangement closely resembles the classical electrical circuit known as a Wheatstone Bridge.
Coil L-l and its condenser constitute a filter circuit tuned to 720 cycles. When switch D-2 is thrown to "Regulate" and the output of the armature is precisely 720 cycles, the impedances of the two parallel paths just described are precisely equal. Equal current flows through each, and the voltage drop through the filter matches exactly the voltage drop through the upper half of T-3 primary. Under these circumstances there is no difference of potential across the bridging circuit (the primary of T-2), no current flows across the bridge, none is induced in the secondary of T-2, the grid bias of V-4 is not altered, and the motor speed does not change.
Consider conditions when this motor has just started and is coming up to speed. The armature output is less than 720 cycles. The bridge is unbalanced, current flowing through the bridging circuit. By virtue of the phaseeffect of the small condenser in L-l, plus that of C-6