The receivers are generally used as the error detector in a servo loop, with a motor doing the heavy lifting. A bare synchro receiver can move small stuff, like a needle in an instrument display.
A lot of military gear used synchros to do math, like targeting torpedoes, before computers. They are still a common position sensor in aircraft. A throttle lever is usually an RVDT these days, similar to a synchro transmitter.
I sort of doubt that they did it that way back in the 1920s-1950s though. Or maybe the receiver ran a big mag amp gizmo that controlled the motor?
LVDTs and RVDTs are a really good technology. I've used LVDTs in scan stage motion controllers, and they work great--competitive with calibrated glass linear scales, but with far less sensitivity to cross-axis motion.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
There were all sorts of things, like amplidynes (getting gain out of a generator by inputting into the field).
One of the RadLab books is "Servomechanisms"
LVDTs can have nm resolution. But they are not very linear or repeatable between units.
d
-phase sine wave and a quadrature sine wave (which is to say a cosine wave) and scale the sum back by 0.707 (which will leave you with the same peak a mplitude as the sine and cosine waves - though it won't peak at the same ti me as either of them peaks.
True. I screwed up. Linear variable transformers and rotary variable transf ormers both work by multiplying the drive waveform by number between +1 an d -1.
Since they are transformers the output lags the drive - the one time I had to worry about it is was by about a degree.
It is a simple-minded system, because it dates back to a time when electron ics had to be kept simple.
-- Bill Sloman, Sydney
ems
Hz
t 0s,
They can't be spectacularly linear. You've got a moving slug that adjusts t he coupling between the diver coil and the receiving coils. They should be pretty repeatable - the coils involved are wound with wire that has a 2% to lerance on its dimensions, but you should be able to get the same numbers o f turns on every winding you ship, and the moving slug and coil formers sho uld be equally close-toleranced. They should be better than Moire gratings - everything is averaged over the whole assembly - even if they can't be as good as an interferometer driven from a genuinely monochromatic source.
-- Bill Sloman, Sydney
For a three-phase synchro system, it is difficult to avoid trigonometry (of 30, 60 and 90 degrees, at least).
The two-DAC system usually creates a two-phase system, at 90 degrees phase shift. It is convertible to three phases using a thing called the Scott T-transformer. It should be in the book.
For your problem, see section V in the book, from page 49 onward.
-- -TV
John Larkin wrote
Indeed; the higher quality aircraft instruments are sunchro driven, not moving coil. So you get a very positive pointer drive, whereas moving coil are affected by the smallest stiction etc.
Most of these
I have one of their pressure gauges in my plane.
Bill Sloman wrote
A "famous" LVDT implementation is the pitch/roll pickoff on a KI256 artificial horizon. The LVDT there is "bent" into a circle.
A couple of firms have emulated that, which is an interesting project. The input to the emulator is generally ARINC429 pitch/roll.
I have a KI256 also; you can buy them cheap enough these days.
Tauno Voipio wrote
I can do trig and all that; not much good at complicated algebra :) At univ, my eyes glazed over at Laplace Transforms but Fourier was fun - at least the practical application of it.
Thanks for your pointer. Yes page 49 seems quite practical.
On a sunny day (Wed, 10 Feb 2021 13:46:15 +0000) it happened Peter wrote in :
I dunno about all this, sounds like ages old stuff I have pitch-roll for a boat here, can display it anyway you like by changing the software...
is just a MEMS chip:
My Xiaomi smartphone has a compass and a level, likely a similar or the same chip.
No wonder planes are expensive and heavy ;-) Save fuel go digital...
This is digressing but you can't certify a ten bob "AHRS" chip as a primary pitch/roll reference.
For a start you need to sense the gravity vector, for the slow background erection, but you also need three yaw gyros; 2 for pitch and roll and one for heading.
All this stuff drifts like hell so it needs to be temperature stabilised.
The mechanical gyros are accepted because they have been around for many decades.
There is probably a tiny bit of 400 Hz vibration in a synchro off null, and that can break up static friction.
There were some needle-type carburetors (British sliding-piston SU, Honda rubber diaphragm) that shouldn't have worked but for engine vibration. Tweaking an SU carb outside a gay bar won me my wife.
I guess there could be some vibration on an airplane too.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Yes, but quad dacs are cheap.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
hahahahaha
AFAICT I will only ever need two outputs, XY, and possibly also generate the reference output.
I have never seen three phases used to transmit a heading in avionics.
What I have seen done, and probably 3 phases, is the transmission of a bearing, from an instrument where you can twiddle a compass card all the way round.
At the bar she told me her MG Midget was running bad. It was idling at
3000 RPM and I always carry a Swiss army knife. Poor girl thought I was a genius.-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
I work with big jets. They use 3-stator synchros for things like engine vane and flap positions, running into a FADEC or some other computer, not directly to an indicator. Maybe because the 3 phases provide failure indication.
Throttle levers tend to be RVDTs for some reason. Failure detection can be done on them, too.
On a 2-phase resolver, four angular positions can lose a signal and still look correct.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
It is not 400Hz but the engine and ariframe vibration that is needed to overcome the stiction in the basic aircraft pointer instruments. In a Piper Navajo simulator there are real aircraft instruments and behind the panel there is a small DC motor with an excentric weight on the shaft to vibrate the panel to keep the instruments alive.
A different story is that modern high quality aircraft instrumenta are currently panel displays without mechanical pointers, see e.g. Garmin G1000 glass cockpit. The attitude and heading references are not gyros anymore, but electronic sensors instead.
-- -TV
Are actual gyros not used any more to sense attitude? What electronic sensor can tell where "down" is? Maybe an accelerometer with a very long time constant?
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
It's a long story, but basically you cannot certify a purely-AHRS solution (3 x acc and 3 x yaw gyro) as a primary pitch and roll reference, for a primary artificial horizon or for an autopilot.
It can be certified for stuff like backup horizon, for weather radar tilt compensation, etc.
For a certified AHRS you need to bring in either airdata (constant airspeed + constant heading -> straight/level flight, to provide the slow background erection) or GPS (constant track + constant ground speed or maybe altitude -> as above). These solutions create problems e.g. an iced-up pitot tube totally kills your reference, or loss of GPS does the same.
But traditional mechanical instruments are acceptable as primary :)
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