On Tuesday, February 18, 2014 9:25:19 AM UTC-8, Xunchen Liu wrote:
> Hi, I've been trying with an instrumentation amplifier. so far, the noise is still large.
>
> just to provide more information. The idea here is that the source of vibration is at the resonance frequency of the tuning fork. So high Q actually helps to tuning fork to pick up the sound.
It might be better to use a microphone, and (in the preamplifier stage) use
a quartz crystal resonator as a filter. The Q is so high, though, that you'll probably
not get much pickup until you damp the crystal (with a parallel resistor).
There's lots of filter circuits in op amp cookbooks that will work, just
be aware that the crystal doesn't pass DC current.
The feedback impedance of a 32 kHz crystal is usually not resistive at the oscillation
frequency, but inductive (so the best gain ISN"T exactly at the oscillation
frequency of the crystal-plus-capacitors in a resonator).
Reply by Phil Hobbs●February 18, 20142014-02-18
On 02/18/2014 02:11 PM, John Larkin wrote:
> On Tue, 18 Feb 2014 12:51:55 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> On 02/18/2014 12:36 PM, John Larkin wrote:
>>> On Tue, 18 Feb 2014 09:25:19 -0800 (PST), Xunchen Liu <xunchen@ualberta.ca>
>>> wrote:
>>>
>>>> Hi, I've been trying with an instrumentation amplifier. so far, the noise is still large.
>>>>
>>>> just to provide more information. The idea here is that the source of vibration is at the resonance frequency of the tuning fork. So high Q actually helps to tuning fork to pick up the sound.
>>>
>>> I don't think that external vibration will couple very well into a tuning-fork
>>> crystal. If it did, the Q would be low, and it's not.
>>>
>>>
>>
>> Tuning forks achieve low coupling to the outside world by balancing the
>> torques exerted on the mount.
>>
>> It sounds like the OP is using it by putting one side up against the
>> vibrating object, though, rather than detecting sound in air. That
>> coupling is mechanically unbalanced, so he might be able to detect it.
>> Lots of scanned-probe microscopes do that sort of thing.
>>
>> Cheers
>>
>> Phil Hobbs
>
> If he can couple asymmetrically into the tines, it could be very
> sensitive, but the crystal would have to be removed from its can.
>
Yup. Otherwise he's dead, just as you say.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Reply by John Larkin●February 18, 20142014-02-18
On Tue, 18 Feb 2014 10:10:20 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:
>On Tuesday, February 18, 2014 12:25:19 PM UTC-5, Xunchen Liu wrote:
>> Hi, I've been trying with an instrumentation amplifier. so far, the noise is still large.
>>
>>
>>
>> just to provide more information. The idea here is that the source of vibration is at the resonance frequency of the tuning fork. So high Q actually helps to tuning fork to pick up the sound.
>
>Why the instrument amp? They are much less flexible than a single opamp.... you can't even roll of the gain with an R/C in the feed back.
>Maybe you could post a circuit diagram.
>
>You could try a Q ~10 bandpass filter, centered on the 32kHz of the tuning fork. That should cut your noise down. (no sense looking at frequencies where there is no signal.)
>
>George H.
A jfet would be a good first gain stage.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by John Larkin●February 18, 20142014-02-18
On Tue, 18 Feb 2014 12:51:55 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>On 02/18/2014 12:36 PM, John Larkin wrote:
>> On Tue, 18 Feb 2014 09:25:19 -0800 (PST), Xunchen Liu <xunchen@ualberta.ca>
>> wrote:
>>
>>> Hi, I've been trying with an instrumentation amplifier. so far, the noise is still large.
>>>
>>> just to provide more information. The idea here is that the source of vibration is at the resonance frequency of the tuning fork. So high Q actually helps to tuning fork to pick up the sound.
>>
>> I don't think that external vibration will couple very well into a tuning-fork
>> crystal. If it did, the Q would be low, and it's not.
>>
>>
>
>Tuning forks achieve low coupling to the outside world by balancing the
>torques exerted on the mount.
>
>It sounds like the OP is using it by putting one side up against the
>vibrating object, though, rather than detecting sound in air. That
>coupling is mechanically unbalanced, so he might be able to detect it.
>Lots of scanned-probe microscopes do that sort of thing.
>
>Cheers
>
>Phil Hobbs
If he can couple asymmetrically into the tines, it could be very
sensitive, but the crystal would have to be removed from its can.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by George Herold●February 18, 20142014-02-18
On Tuesday, February 18, 2014 12:25:19 PM UTC-5, Xunchen Liu wrote:
> Hi, I've been trying with an instrumentation amplifier. so far, the noise is still large.
>
>
>
> just to provide more information. The idea here is that the source of vibration is at the resonance frequency of the tuning fork. So high Q actually helps to tuning fork to pick up the sound.
Why the instrument amp? They are much less flexible than a single opamp.... you can't even roll of the gain with an R/C in the feed back.
Maybe you could post a circuit diagram.
You could try a Q ~10 bandpass filter, centered on the 32kHz of the tuning fork. That should cut your noise down. (no sense looking at frequencies where there is no signal.)
George H.
Reply by Phil Hobbs●February 18, 20142014-02-18
On 02/18/2014 12:36 PM, John Larkin wrote:
> On Tue, 18 Feb 2014 09:25:19 -0800 (PST), Xunchen Liu <xunchen@ualberta.ca>
> wrote:
>
>> Hi, I've been trying with an instrumentation amplifier. so far, the noise is still large.
>>
>> just to provide more information. The idea here is that the source of vibration is at the resonance frequency of the tuning fork. So high Q actually helps to tuning fork to pick up the sound.
>
> I don't think that external vibration will couple very well into a tuning-fork
> crystal. If it did, the Q would be low, and it's not.
>
>
Tuning forks achieve low coupling to the outside world by balancing the
torques exerted on the mount.
It sounds like the OP is using it by putting one side up against the
vibrating object, though, rather than detecting sound in air. That
coupling is mechanically unbalanced, so he might be able to detect it.
Lots of scanned-probe microscopes do that sort of thing.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Reply by John Larkin●February 18, 20142014-02-18
On Tue, 18 Feb 2014 09:25:19 -0800 (PST), Xunchen Liu <xunchen@ualberta.ca>
wrote:
>Hi, I've been trying with an instrumentation amplifier. so far, the noise is still large.
>
>just to provide more information. The idea here is that the source of vibration is at the resonance frequency of the tuning fork. So high Q actually helps to tuning fork to pick up the sound.
I don't think that external vibration will couple very well into a tuning-fork
crystal. If it did, the Q would be low, and it's not.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Reply by Xunchen Liu●February 18, 20142014-02-18
Hi, I've been trying with an instrumentation amplifier. so far, the noise is still large.
just to provide more information. The idea here is that the source of vibration is at the resonance frequency of the tuning fork. So high Q actually helps to tuning fork to pick up the sound.
Reply by John Larkin●February 14, 20142014-02-14
On Thu, 13 Feb 2014 19:20:00 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>On Thu, 13 Feb 2014 19:44:13 -0700, Jim Thompson
><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>
>>On Thu, 13 Feb 2014 18:07:35 -0800, John Larkin
>><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>On Wed, 12 Feb 2014 10:34:57 -0800 (PST), Xunchen Liu <xunchen@ualberta.ca>
>>>wrote:
>>>
>>>>Hi sorry for cross posting from sci.optics. I just summarize what I want to do:
>>>>
>>>>I am trying to use a quartz crystal tuning fork at 32768 Hz, 12.5 pF, 35 kOhm as a sensitive sound detector at its resonance frequency from its piezoelectric signal.
>>>
>>>I'd think that external vibration would couple very poorly into a tuning-fork
>>>crystal. Reciprocity, COE, high-Q, stuff like that.
>>
>>And other such buzz words >:-}
>
>The meaning should be obvious to any reasonable engineer. Do I need to spell it
>out for you?
>
>Do you think that external vibration will couple well into a tuning fork
>crystal? Say why or why not.
Well? Can't remember any of that MIT physics? I took two great physics
courses at Tulane, had fun, learned a lot. [1]
TCA = Thompson Chokes Again.
[1] in those days, the Tulane physics department had a subcritical
nuclear reactor, a big stainless tank full of water and uranium rods.
They let us handle the fuel rods. They had a high-power unshielded
x-ray source too, with tape on the floor to define the keepout region.
The old Physics building was brick and wood construction with copper
nails, for turn-of-the century magnetics experiments.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by Bill Sloman●February 14, 20142014-02-14
On Friday, 14 February 2014 14:20:00 UTC+11, John Larkin wrote:
> On Thu, 13 Feb 2014 19:44:13 -0700, Jim Thompson=20
> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:=20
> >On Thu, 13 Feb 2014 18:07:35 -0800, John Larkin=20
> ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
> >>On Wed, 12 Feb 2014 10:34:57 -0800 (PST), Xunchen Liu <xunchen@ualberta=
.ca>
> >>wrote:=20
> >>
> >>>Hi sorry for cross posting from sci.optics. I just summarize what I wa=
nt to do:=20
> >>>=20
> >>>I am trying to use a quartz crystal tuning fork at 32768 Hz, 12.5 pF, =
35 kOhm as a sensitive sound detector at its resonance frequency from its p=
iezoelectric signal. =20
> >>=20
> >>I'd think that external vibration would couple very poorly into a tunin=
g-=20
> >>fork crystal. Reciprocity, COE, high-Q, stuff like that.=20
> >=20
> >And other such buzz words >:-}
> =20
> The meaning should be obvious to any reasonable engineer. Do I need to sp=
ell =20
> it out for you?
You could probably provide a certain amount of amusement by trying. You did=
n't pay enough attention to your lectures at Tulane to be able to produce t=
he routine answers. Your intuitive grasp of what's going on is probably fin=
e, but you aren't somebody I'd turn to for a helpful exposition of the theo=
ry
=20
> Do you think that external vibration will couple well into a tuning fork=
=20
> crystal? Say why or why not.
The right answer is probably that we don't know, since we don't know exactl=
y which tuning fork crystal he is trying to use. We do know that he's looki=
ng for acoustic vibrations, which is a sub-set of all the possible external=
vibrations.
--=20
Bill Sloman, Sydney