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From: Chuck Harris on 7 Apr 2006 11:12 John Larkin wrote: > The one we used has a lamination suspended on wires, that moves with > inclination and varies the reluctance of a couple of coils, a lot like > an LVDT. I think it's filled with oil for damping. I used this > oscillator to excite it, and a synchronous detector+lowpass filter to > condition the output. Amplitude stability was important, distortion > much less so. It also turns out that the output is fairly nonlinear > and asymmetric at larger inclinations, so I had to compensate for > that. This was about 1972, and I was just a brat, so I can't claim it > was the most brilliant design possible. I just thought the oscillator > was cute. Oscillators have always been one of my favorite things, and simple ones that perform nicely, doubly so... but it still is just a double coil Hartley ;-)... probably invented when you were in diapers. > > I had the guys in the machine shop donate a 55-gallon drum. We placed > it on the ground-floor concrete slab, filled it with sand, and clamped > a 2" thick machined-flat steel plate on top. The guys fabbed a neat > platform, pivoted on ball bearings, driven by a micrometer, so I could > crank in angles with arc-second precision (finding horizontal is easy: > just reverse the Talyvel.) It worked great as long as nobody walked > around nearby and bent the slab. I was doing stuff like that in a laser laboratory at the university of Maryland, in a similar time frame. Seeing the vibration from a person walking down the hall, being transmitted through air suspension legs and into an interferometer bolted onto a 2000 pound optical table gives one new insight into his understanding of how movable the unmovable really is. -Chuck Harris
From: John Larkin on 7 Apr 2006 11:25 On Fri, 07 Apr 2006 11:12:32 -0400, Chuck Harris <cf-NO-SPAM-harris(a)erols.com> wrote: >John Larkin wrote: > >> The one we used has a lamination suspended on wires, that moves with >> inclination and varies the reluctance of a couple of coils, a lot like >> an LVDT. I think it's filled with oil for damping. I used this >> oscillator to excite it, and a synchronous detector+lowpass filter to >> condition the output. Amplitude stability was important, distortion >> much less so. It also turns out that the output is fairly nonlinear >> and asymmetric at larger inclinations, so I had to compensate for >> that. This was about 1972, and I was just a brat, so I can't claim it >> was the most brilliant design possible. I just thought the oscillator >> was cute. > >Oscillators have always been one of my favorite things, and simple ones >that perform nicely, doubly so... but it still is just a double coil >Hartley ;-)... probably invented when you were in diapers. > Before. Also invented before the transistor. What's fun about the oscillator is the way the amplitude is regulated, not by hard limiting and not by transconductance nonlinearity, but by peak detection and feedback gain control. You can say "that's just a Hartley" or you could say "it's really cool the way the amplitude limits and the way the tc's cancel." Different people have different attitudes about stuff like this. >> >> I had the guys in the machine shop donate a 55-gallon drum. We placed >> it on the ground-floor concrete slab, filled it with sand, and clamped >> a 2" thick machined-flat steel plate on top. The guys fabbed a neat >> platform, pivoted on ball bearings, driven by a micrometer, so I could >> crank in angles with arc-second precision (finding horizontal is easy: >> just reverse the Talyvel.) It worked great as long as nobody walked >> around nearby and bent the slab. > >I was doing stuff like that in a laser laboratory at the university of >Maryland, in a similar time frame. Seeing the vibration from a person walking >down the hall, being transmitted through air suspension legs and into >an interferometer bolted onto a 2000 pound optical table gives one new >insight into his understanding of how movable the unmovable really is. Yeah, it's fun to do mechanical stuff now and then, and not just electronics. John
From: Chuck Harris on 7 Apr 2006 12:20 John Larkin wrote: > On Fri, 07 Apr 2006 11:12:32 -0400, Chuck Harris > <cf-NO-SPAM-harris(a)erols.com> wrote: > >> John Larkin wrote: >> >>> The one we used has a lamination suspended on wires, that moves with >>> inclination and varies the reluctance of a couple of coils, a lot like >>> an LVDT. I think it's filled with oil for damping. I used this >>> oscillator to excite it, and a synchronous detector+lowpass filter to >>> condition the output. Amplitude stability was important, distortion >>> much less so. It also turns out that the output is fairly nonlinear >>> and asymmetric at larger inclinations, so I had to compensate for >>> that. This was about 1972, and I was just a brat, so I can't claim it >>> was the most brilliant design possible. I just thought the oscillator >>> was cute. >> Oscillators have always been one of my favorite things, and simple ones >> that perform nicely, doubly so... but it still is just a double coil >> Hartley ;-)... probably invented when you were in diapers. >> > > Before. Also invented before the transistor. Definitely, but I was thinking of when the transistorized version of the old tube Hartley was first tried. It had to have been before '63, but I suspect that it was within a few years of the invention of the transistor. What's fun about the > oscillator is the way the amplitude is regulated, not by hard limiting > and not by transconductance nonlinearity, but by peak detection and > feedback gain control. > > You can say "that's just a Hartley" or you could say "it's really cool > the way the amplitude limits and the way the tc's cancel." Different > people have different attitudes about stuff like this. Well, I think it's cool how a emitter follower creates its negative feedback control, but that's the nature of this business, lots of little cool things that we all take for granted. >>> I had the guys in the machine shop donate a 55-gallon drum. We placed >>> it on the ground-floor concrete slab, filled it with sand, and clamped >>> a 2" thick machined-flat steel plate on top. The guys fabbed a neat >>> platform, pivoted on ball bearings, driven by a micrometer, so I could >>> crank in angles with arc-second precision (finding horizontal is easy: >>> just reverse the Talyvel.) It worked great as long as nobody walked >>> around nearby and bent the slab. >> I was doing stuff like that in a laser laboratory at the university of >> Maryland, in a similar time frame. Seeing the vibration from a person walking >> down the hall, being transmitted through air suspension legs and into >> an interferometer bolted onto a 2000 pound optical table gives one new >> insight into his understanding of how movable the unmovable really is. > > Yeah, it's fun to do mechanical stuff now and then, and not just > electronics. If I could support myself, and my family, in the manner to which we have become accustomed, I would happily spend the rest of my life providing EE support for a university research lab. It is a great job for the jack-of-all-trades types like myself... but alas, there is barely enough money in it to support an already well supported grad student. -Chuck Harris
From: John Larkin on 7 Apr 2006 12:50
On Fri, 07 Apr 2006 12:20:25 -0400, Chuck Harris <cf-NO-SPAM-harris(a)erols.com> wrote: >> >> Yeah, it's fun to do mechanical stuff now and then, and not just >> electronics. > >If I could support myself, and my family, in the manner to which we have >become accustomed, I would happily spend the rest of my life providing EE >support for a university research lab. It is a great job for the >jack-of-all-trades types like myself... but alas, there is barely enough >money in it to support an already well supported grad student. That's about what Win does, I think. It's fun to be around all the physics and stuff, as a dilettante, without the tedium of having to get a PhD and all the post-doc stuff. Plus, it gives you time to write books (well, two editions anyhow.) John |