I am a volunteer at an aviation museum. I am trying to develop a solid state replacement for a WWII gun turret servo. I am trying to use the existing sensors (selsyns), but replace the servo (tubes and transformers) and motor controller (amplidyne).
The system supply is 115VAC, 400Hz. The selsyns produce 57.5VAC, 400HZ, that varies in amplitude and phase. Amplitude indicates the angular error magnitude, and phase (0 or 180) indicates the error direction. The servo monitored the selsyn output, and generated a +/- voltage difference between the inphase and out of phase sides of the servo amp. This +/- difference fed a bidirectional motor controller.
I figure I can use the same basic approach, with two sides to the solid state servo amp -- an in phase and an out of phase side. So, what I need is a circuit to handle the fixed amplitude 115VAC supply/phase reference, and the 57.5VAC variable amplitude/phase input signal.
I was thinking that some form of FET source follower for each side might be a good start for this. Each side would be supplied by one output from a bridge-like rectifier (half-wave in-phase and out of phase), and the input signal to both sides would be half rectified (half-wave varable amplitude and phase). Each side would then output a voltage proportional to the input signal and its phase (0 or 180). The rectified input signal voltage could be easily reduced using a voltage divider (e.g. 10:1 for 0-6V at the gate).
What do I do about the 115VAC supply voltage? What is a good way to reduce that to something that a simple FET could handle (e.g. 0-16V at the drain)?
What size source resistor is needed? (The voltage difference sensor between the two sides is essentially a high impedance opamp, whose output drives a bidirectional motor controller -- 0 for full reverse, +5 for full forward, and 2.5V for no motion.)
What transistor number should I use? (Precision is not required -- it's just for demonstration, but the environment could have temp extremes, especially on the high side -- closed airplane sitting in the sun.)
Any help would be appreciated.
--jon
The system supply is 115VAC, 400Hz. The selsyns produce 57.5VAC, 400HZ, that varies in amplitude and phase. Amplitude indicates the angular error magnitude, and phase (0 or 180) indicates the error direction. The servo monitored the selsyn output, and generated a +/- voltage difference between the inphase and out of phase sides of the servo amp. This +/- difference fed a bidirectional motor controller.
I figure I can use the same basic approach, with two sides to the solid state servo amp -- an in phase and an out of phase side. So, what I need is a circuit to handle the fixed amplitude 115VAC supply/phase reference, and the 57.5VAC variable amplitude/phase input signal.
I was thinking that some form of FET source follower for each side might be a good start for this. Each side would be supplied by one output from a bridge-like rectifier (half-wave in-phase and out of phase), and the input signal to both sides would be half rectified (half-wave varable amplitude and phase). Each side would then output a voltage proportional to the input signal and its phase (0 or 180). The rectified input signal voltage could be easily reduced using a voltage divider (e.g. 10:1 for 0-6V at the gate).
What do I do about the 115VAC supply voltage? What is a good way to reduce that to something that a simple FET could handle (e.g. 0-16V at the drain)?
What size source resistor is needed? (The voltage difference sensor between the two sides is essentially a high impedance opamp, whose output drives a bidirectional motor controller -- 0 for full reverse, +5 for full forward, and 2.5V for no motion.)
What transistor number should I use? (Precision is not required -- it's just for demonstration, but the environment could have temp extremes, especially on the high side -- closed airplane sitting in the sun.)
Any help would be appreciated.
--jon