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Old 6th January 2013, 02:51 PM   #1471
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Quote:
Originally Posted by davada View Post
From it's description I think the Shibasoku is a heterodyne process. It's a very sophisticated selective voltmeter.

But since no one has a service manual for it who knows.

Cheers,
AFAIR you are close, I once actually had a manual . I posted those parts and literally as the letter dropped into the bin I overheard the postmaster warning the next customer not to put anything non-flat in the generic mail box, hopefully it won't jam the automatic sorter. Keep an eye out, there are plenty more.
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Old 6th January 2013, 03:00 PM   #1472
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Here's my plot of the PV/FET circuit, a 1500/100 Ohm bridge, nulled against another 1500 Ohm resistor and the FET (J310) tuned to 100 Ohms. The seconds can be nulled to almost the noise (I used .033u across the PV don't know how low you can go). This is at ~.9V p-p on the FET, if the distortion is low order it should drop dramatically (60dB/dec) at lower levels.

This is about as good as I could null the fundamental stepping 1mV or so at a time on the PV drive (100 Ohm in series with the LED).
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File Type: jpg fetres.JPG (113.7 KB, 156 views)
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Old 6th January 2013, 03:08 PM   #1473
davada is online now davada  Canada
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Quote:
Originally Posted by scott wurcer View Post
AFAIR you are close, I once actually had a manual . I posted those parts and literally as the letter dropped into the bin I overheard the postmaster warning the next customer not to put anything non-flat in the generic mail box, hopefully it won't jam the automatic sorter. Keep an eye out, there are plenty more.
LOL.

I got ____ for that once too.

It's about postage not the machine jamming.

I mailed ordered some T03 can trans years ago. The guy stuck them in one of those padded flat packages. When I got them the pins were bent flat against the case. Maybe they go through a roller at the sorting facility.
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Last edited by davada; 6th January 2013 at 03:19 PM.
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Old 6th January 2013, 03:49 PM   #1474
davada is online now davada  Canada
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Originally Posted by jan.didden View Post
Lock-in amplifier principle? I've been looking at some PAR units, but not sure if it is worth the hassle.

jan

Hi Jan,

You have giving a very interesting idea for a peak detector similar to lock in amplifier.

Thanks,
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Old 6th January 2013, 03:55 PM   #1475
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Quote:
Originally Posted by scott wurcer View Post
Here's my plot of the PV/FET circuit, a 1500/100 Ohm bridge, nulled against another 1500 Ohm resistor and the FET (J310) tuned to 100 Ohms. The seconds can be nulled to almost the noise (I used .033u across the PV don't know how low you can go). This is at ~.9V p-p on the FET, if the distortion is low order it should drop dramatically (60dB/dec) at lower levels.

This is about as good as I could null the fundamental stepping 1mV or so at a time on the PV drive (100 Ohm in series with the LED).
Why does the cap drop H2? Thx-RNMarsh
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Old 6th January 2013, 04:04 PM   #1476
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I'm completely lost now--why are we talking about subsampling techniques, FFTs and lock-in amplifiers as level detector for the amplitude stabilization loop? The response of the level detector needs to be fast (ideally within a small fraction of a period), or loop compensation will become a tremendous nightmare. Also we neither need ppm precision nor are we looking for µV signals burried in noise..?

Samuel
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Old 6th January 2013, 04:29 PM   #1477
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Originally Posted by RNMarsh View Post
Why does the cap drop H2? Thx-RNMarsh
Non-linear Cgd and Cgs, the PV looks like a current source so the displacement current directly adds to the control signal.
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Old 6th January 2013, 06:01 PM   #1478
davada is online now davada  Canada
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Originally Posted by Samuel Groner View Post
I'm completely lost now--why are we talking about subsampling techniques, FFTs and lock-in amplifiers as level detector for the amplitude stabilization loop? The response of the level detector needs to be fast (ideally within a small fraction of a period), or loop compensation will become a tremendous nightmare. Also we neither need ppm precision nor are we looking for µV signals burried in noise..?

Samuel
Hi Samuel,

There is more than one subject being discussed here.

I don't need a fast detector for what I'm doing. These methods wouldn't work for a conventional multiplier like a Jfet type.
Other detection methods are being discussed for an already stabilized loop that just needs to be brought to a reference level.
Additionally these methods can be used for other purposes that don't require fast loops like auto null etc.

Cheers,
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Last edited by davada; 6th January 2013 at 06:06 PM.
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Old 6th January 2013, 07:15 PM   #1479
davada is online now davada  Canada
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This one I'm optimistic about. I think it might be fast enough for conventional loops.

This is a functional simulation.

The signal source is squared by a multiplier. The signal source is feed to the input of a VCA and it's output is squared by a multiplier. The squared source and VCA are input to a differencing amplifier and the output of the difference amplifier feeds an integrator. The DC from the output of the integrator provides an error signal Vc for the VCA. When the squared source and squared output of the VCA are equal the output of the difference amplifier is null, 0Vdc average and the ripple component is in the low uV's. If the output of the VCA is less than the source the DC component at the output of the difference amp is negative and the integrator ramps up. if the output of the VCA is greater than the source the DC component at the output of the difference amp is positive and the integrator ramps down. The system locks the VCA output level to the amplitude of the source and the output of the integrator is a DC value equal to the peak of the source.

The speed of the system response is dependent on the response of the multipliers and the tau of the integrator. The output ripple is a function of the null and not a function of frequency. Therefore the integrator TC can be short. The LP effect of the integrator does help to minimized the ripple though.

The system is not sensitive to component tolerance and any error can be trimmed out.

The last two plots show output ripple from the integrator. The second one for a longer integrator tau.
Attached Images
File Type: png det1.PNG (47.5 KB, 128 views)
File Type: png det2.PNG (73.2 KB, 125 views)
File Type: png det3.PNG (75.0 KB, 123 views)
File Type: png det4.PNG (64.7 KB, 120 views)
File Type: png det5.PNG (63.8 KB, 46 views)
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Last edited by davada; 6th January 2013 at 07:18 PM.
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Old 6th January 2013, 07:27 PM   #1480
davada is online now davada  Canada
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This is a 10Hz 1V modulation on a 5V 1KHz signal to show the tracking of the output signal from the integrator.

I hope it works in practice.
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