Old School Resolvers

Hi, Bart. Before digital logic, resolvers were the best way to get continuous angular data on a rotating object. In fact, because of their speed of response and high resistance to electrical noise, they're still frequently used in many applications.

The simplest resolvers are six wire -- they have an AC power input (2 wires), and a sine (2) and cosine (2) output. If your meter is true RMS up to the recommended frequency, you can just input the required voltage/frequency (they're relatively high impedance, you can probably drive it with a function generator output), and measure the magnitude of the sine and cosine outputs. A quick check would be to 1) ohm out each pair to check for continuity, 2) ohm out between pairs to check for shorts, and then 3) apply a voltage and see if there's an output.

But sadly, it usually isn't that simple. There are many different types of resolvers, and figuring out a way to do a quick check (like powering up the encoder and looking for square wave outputs when you spin the shaft) kind of depends on knowing what you've got.

Start with the data sheet on the resolver -- it's usually available from the manufacturer if they still make it (and sometimes, even if they don't). Either that, or you can get the schematic of the interface and try to muscle it out from there.

Possibly if you could mention what kind of resolver you have, someone could provide more help.

Good luck Chris

So let me guess, do these have an AC dipole on the shaft (or the inverse), and respective biphase pickup windings?

Makes good sense, kind of AM-ey though. Low impedance would bring good noise immunity, I suppose.

I wonder if there's a rotational 'doppler effect' going on when RPM ~ carrier F? Just wandering (not necessarily wondering)...

Tim

Hi, Tim. Most modern resolver signals are in the KHz range -- a lot faster than rotation will ever be. But some older ones do work at 60Hz

-- I'd guess you might get that effect.. ;-)

Cheers Chris

These "resolvers" are the same as "selsyns" or "syncros" aren't they? You can tie two together and if you turn one, the other turns?

I remember when "selsyns" came up in SED once, somebody said he played with a pair coupled together and found that he could spin one at a certain rate and produce feedback that made them both accelerate out of control.

I'd believe *THAT* just about as much as I'd believe a newborn baby can pick up and throw a full-grown elephant the length of a football field.

(Reference "perpetual motion machines"...)

Wrong reference. :) These devices have external power applied.

Ahhh... In that case, I retract the previous.

I was assuming from comments scattered about in the thread that these "selsyn" things (which I'm not familiar with, nor really interested enough in to bother trying to read up on at the moment) were similiar to stepper motors - take two same type/size steppers and wire them together, then spin one of the shafts and watch what happens.

Yes, Virginia, I'm aware that there are losses in that system, but I'm not ambitious enough to bother listing them. For illustrative purposes, however, saying "twist one shaft and the other shaft twists the same amount/ at the same speed" is an accurate enough statement.

Nope.

they're like steppers but with AC magnetic field instead of permanment magnets. also sesigned not to "cog"

Bye. Jasen