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From: delo on 20 Apr 2010 05:20

"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> ha scritto nel
messaggio news:3frps5h95f40puq4ghqv2g70k557s847f6(a)4ax.com...
>
> Can anybody suggest a good one?
>
> John
>
try:

www.hnsa.org/doc/neets/mod15.pdf

bye
delo


From: John Larkin on 20 Apr 2010 07:11
On Mon, 19 Apr 2010 20:50:35 -0700, Tim Wescott <tim(a)seemywebsite.now>
wrote:

>John Larkin wrote:
>> Can anybody suggest a good one?
>
>Ha ha ha ha ha he he he he he ho ho ho ho ho aaaaaaaaaaaaaaaaagh!
>
>(I'm not making fun of you here, that's hysterical laughter).

There seems to be some stuff from, say, 1955 or so. I don't suppose
much has changed.

>
>Call Renco Encoders and see if you can sweet-talk them out of a copy of
>"Feedback Devices in Motion Control Systems", by Robert M. Setbacken.
>
>Then call Moog Components -- wade through the Moog website and find the
>guys that sell the precision industrial and aerospace encoders. Sweet
>talk them, too.
>
>Be aware that all the electronics whizzes who worked on encoders have
>died of old age -- it's all mechanical engineers; they know bearings,
>they know winding machines, and they know how to test things, but when
>you start asking questions about impedance vs. frequency and other
>seemingly obvious things the best you'll get is a friendly shrug.

Seems that way. A lot of the books and lit seem cartoonish.

>
>They're variable transformers. They're really inefficient. Their
>impedance is pretty close to the wiring resistance plus the inductance
>times radian frequency (no surprise there). They work over an
>astonishingly large frequency range, although they are traditionally
>only specified at the frequency that the first customer wanted to use.
>The drive amplitude is specified in voltage, although if you read
>between the lines they're limiting the I^2R losses in the primary. Try
>to ask the guys who design them these days and at best you'll get a
>friendly shrug...
>
>You can order them specified for other frequencies, or sizes, for "some"
>NRE. "Some" is relative, and Moog is an aerospace company...
>
>How tightly are you gonna simulate the resolvers? Just behavioral?
>1st-order with inductances and winding resistance? Parallel
>capacitance? Electrical nonlinear effects? Spatial nonlinear effects?
> Are you gonna simulate multi-speed resolvers?

My gadget is going to be transformers, adcs, dacs, and an FPGA.
Whatever I can do with that. I'll be generating low-power signals into
an electronics box that thinks it's connected to an LVDT or a synchro.
It's representing mechanical positions of things like flaps or bits of
engines, so it doesn't need arc-second accuracy. Stuff like
multi-speed would be easy.

>
>There's probably a market for a general-purpose resolver simulator, and
>possibly even more so for a general-purpose resolver _meter_ (I recall
>looking and not finding one, at a time that one was desperately needed).

The meters are around.

http://www.naii.com/Angle-Position-Indicators/PSC8

http://www.controlsciences.com/

http://peakelectronics.com/index.php?option=com_content&task=view&id=36&Itemid=62


I'll have to get one if I go ahead with this project. I already have a
couple of those old 6-dial variable-ratio transformer boxes, the
ppm-accurate things that last forever... left over from an LVDT
project.

>
>But there's lots of metrology issues to overcome if you want the meter
>or simulator to exceed the accuracy that you can get from a resolver --
>the really good ones work down to arc seconds, which is "don't breath"
>territory if you want to check out the physical system.

16 bit electronics should work. There are lots of affordable sub-MHz
16-bit ADCs and DACs around nowadays.

John

From: Spehro Pefhany on 20 Apr 2010 08:22
On Tue, 20 Apr 2010 04:11:50 -0700, the renowned John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:


>My gadget is going to be transformers, adcs, dacs, and an FPGA.
>Whatever I can do with that. I'll be generating low-power signals into
>an electronics box that thinks it's connected to an LVDT or a synchro.
>It's representing mechanical positions of things like flaps or bits of
>engines, so it doesn't need arc-second accuracy. Stuff like
>multi-speed would be easy.

I was thinking a bit about this recently-- it would have been handy to
have an LVDT simulator at the time. In particular, how to generate a
simulated output that has a variable phase with respect to the
externally supplied input. Thinking maybe a Hilbert tranform in an
FPGA..


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff(a)interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
From: John Larkin on 20 Apr 2010 09:59
On Tue, 20 Apr 2010 08:22:57 -0400, Spehro Pefhany
<speffSNIP(a)interlogDOTyou.knowwhat> wrote:

>On Tue, 20 Apr 2010 04:11:50 -0700, the renowned John Larkin
><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:
>
>
>>My gadget is going to be transformers, adcs, dacs, and an FPGA.
>>Whatever I can do with that. I'll be generating low-power signals into
>>an electronics box that thinks it's connected to an LVDT or a synchro.
>>It's representing mechanical positions of things like flaps or bits of
>>engines, so it doesn't need arc-second accuracy. Stuff like
>>multi-speed would be easy.
>
>I was thinking a bit about this recently-- it would have been handy to
>have an LVDT simulator at the time. In particular, how to generate a
>simulated output that has a variable phase with respect to the
>externally supplied input. Thinking maybe a Hilbert tranform in an
>FPGA..
>

The basic LVDT or synchro simulation doesn't need phase shift, just
amplitude scaling. In real life, there are some phase shifts in the
signals, from inductive and capacitive effects, but they are usually
minor. I'm leaning towards overkill on the FPGA so that we could have
enough resources to do stuff like phase shifts. Maybe a customer would
want us to simulate some phase shifts, to sim cabling capacitance or
something.

Since we could measure an external excitation frequency, a simple
delay line (RAM based fifo) or some integrators+summers could do the
phase shifting. But things like Hilberts aren't hard if the signal
frequency is low.

John


From: VWWall on 20 Apr 2010 11:57
John Larkin wrote:
> On Mon, 19 Apr 2010 17:24:14 -0700, VWWall <vwall(a)large.invalid>
> wrote:
>
>> John Larkin wrote:
>>> Can anybody suggest a good one?
>>>
>> For their use in old time systems, Rad Lab Series Vol.21.
>
> I have that. And most of the other books don't seem to be much newer!
>
>> If you need to connect between a synchro and a resolver, use a Scott-T
>> transformer. :-)
>
> An expensive transformer seems to be a silly way to do a little trig.
> Adding another multiply to an ARM program costs ... calculates
> furiously ... $0.00.
>
You didn't get it, did you? :-)

> I'm contemplating designing an LVDT/synchro/resolver simulator. The
> sensible way seems to be to digitize the excitation voltage and make
> the various winding voltages with DACs, and do all the rest in a uP or
> FPGA.
>
Lotsa Luck!

--
Virg Wall, P.E.
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