Figure 2-18.--Simplifled converter block diagram (direction or speed).

Figure 2-18.--Simplifled converter block diagram (direction or speed).

direct current at a level dependent upon the amplitude

phase differences between the input and output

of the signal voltage from the synchro stator.

synchros) from being reflected into the converter. The

amplified signal is transformed into sufficient amplitude

The dc signal is then fed into a ring-modulator stage

and is applied with the outputs of the two other channels.

that is excited by the voltage from a 400-Hz excitation

transformer. The output of the ring modulator is a

400-Hz sine wave with an amplitude proportional to the

CONVERTER

magnitude of the dc signal. Two power transistors

operating in the class B push-pull amplifies the 400-Hz

signal.

The converter also contains two chassis that are the

same, one for direction and one for speed. The principles

The amplified 400-Hz signal is sent through an

of operation of one apply to the other. Each chassis

output transformer that steps up the amplitude to 90

consists of three channels that are alike in circuitry and

volts, the required level for excitation of a type 15CT4

operation; thus, the principle of operation of only one

synchro control transformer.

channel is discussed. (See fig. 2-18.)

MAINTENANCE

The sine-wave output from one stator winding of an

external synchro or the synchro isolation amplifier is

applied to the primary winding of the input transformer

Once initially set up for proper operation, the

of the converter. The stepped down signal is sent to the

synchro signal converter and isolation amplifier unit

ring-demodulator stage. The ring-demodulator stage is

requires a minimum of maintenance. As with all

excited by the voltage from a 60-Hz excitation

transistorized units, heat can be a problem, and careful

transformer. The sine wave from the synchro is either in

selection of location is necessary.

phase or 180 out of phase with the excitation voltage.

Preventive maintenance should be limited to clean-

If the sine wave is in phase, the demodulated signal is a

ing all units periodically.

positive, pulsating dc voltage. If the sine wave is out of

Corrective maintenance requires the use of specific

phase, the demodulated signal is a negative, pulsating

metering, outlined in the manufacturer's technical man-

dc voltage. The pulsating dc voltage enters a low-pass

ual

filter network. The output of the filter network is pure

2-18