A control device suitable for synchros comprising three stator windings. The device comprises four circuit branches with the inputs of the first and the second branches interconnected to receive a first voltage from the ends of the stator windings of the synchro transmitter and with the inputs of the third and the fourth branches interconnected to receive a second voltage from the ends of the stator windings of the synchro transmitter. Two adder elements supply control voltages to the stator windings of the synchro receiver. Two inputs of the first adder are connected to the outputs of the first and the third branches, respectively and the two inputs of the secnd adder are connected to the outputs of the second and the fourth branches. These branches have transfer functions in the form sin (.alpha.+.phi.1), sin (.alpha.+.phi.2), sin (.alpha.+.phi.3), sin (.alpha.+.phi.4), respectively, wherein .alpha. represents the information supplied by a digital element and .phi.1, .phi.2, .phi.3, .phi.4 represent the differentphase shift angles. Used to display the position on the instrument panel of aeroplanes.

A phase sensitive demodulator which also provides automatic compensation for variations in the AC reference voltage is shown. The same reference voltage used in generating the signal to be demodulated is itself demodulated and summed with a DC reference value to develop a control signal which is used to cause more or less of the signal to be demodulated as the reference voltage rises and falls thereby resulting in an output which does not change with changes in reference voltage.

A synchronizer system where a positioned synchro transmitter has a rotor excited from an a.c. source and a demodulator operating by momentarily sampling the output of the transmitter once every n cycles of the voltage from the a.c. source where n is greater than 1. An integrator is responsive to the pulsed output of the demodulator with a feedback network responsive to the integrator for controlling the instant of sampling the output to null the output voltage. The integrator may be latched at any phase angle thereafter to cause production of an error signal from the demodulator proportional to further relative rotation in the transmitter.

A demodulator for signals angularly related to the position of a rotor of a synchro or resolver uses, in one embodiment, only one transformer in a circuit for subtracting, adding, and phase shifting the signals to produce a single signal phase shifted in proportion to the rotor angle. In another embodiment, a transformerless circuit uses an operational amplifier to derive the phase shifted signal. The phase shifted signal is compared with a reference signal to produce a rectangular wave with a variable duty cycle, which is integrated to produce a DC voltage representing the rotor angle. A pair of the circuits are used in an altitude warning system connected to synchros for the actual altitude and the command altitude of an aircraft. The derived phase shifted signals from both synchros are compared to produce a rectangular wave with a variable duty cycle, which is integrated and compared with voltages representing preselected altitudes to indicate when the aircraft is at those altitudes.

Resolvers are in common use as angular position sensing devices. Such resolvers normally require difficult to generate sine-wave excitation signals, and extensive decoding circuitry for producing an output signal related to angular position. The subject apparatus utilizes a generator to produce a rectangular-wave timing signal. A logic circuit receives the timing signal and responsively produces first and second rectangular-wave excitation signals, which are delivered to respective stator coils of a resolver. A decoding circuit receives one of the excitation signals and the phase encoded signal magnetically induced in the rotor coil of the resolver, and produces an angular position signal having a duty cycle responsive to the phase difference between the received signals.