Maker Pro
Maker Pro

Oscillator circuit for 32.768 kHz quartz tuning fork crystal element immersed in water

S

Steve

Jan 1, 1970
0
It is possible for the tuning fork element of a 32.768 kHz quartz
crystal to be used in an oscillator circuit if the element has been
exposed from its case and immersed in water ? Or is its Q factor now
too low ? The element exposed to air will produce slightly higher
frequencies than 32.768 kHz when used in a CMOS 4069 inverter gate
circuit using a 10 M ohm resistor (gate out-to-input) and 10 pF from
gate inverting input to ground.
 
R

Rich Grise

Jan 1, 1970
0
It is possible for the tuning fork element of a 32.768 kHz quartz
crystal to be used in an oscillator circuit if the element has been
exposed from its case and immersed in water ? Or is its Q factor now
too low ? The element exposed to air will produce slightly higher
frequencies than 32.768 kHz when used in a CMOS 4069 inverter gate
circuit using a 10 M ohm resistor (gate out-to-input) and 10 pF from
gate inverting input to ground.

It won't oscillate at all, unless it's mind-bogglingly overdriven (which
is likely to break the crystal) and you'd be lucky to get 3 KHz out of
it even then.

Check the viscosity of water vs. the viscosity of air.

An ordinary bimorph might be made to oscillate, but then you'd have a
very expensive ultrasonic cleaner. ;-P

Sorry,
Rich
 
It won't oscillate at all, unless it's mind-bogglingly overdriven (which
is likely to break the crystal) and you'd be lucky to get 3 KHz out of
it even then.

Check the viscosity of water vs. the viscosity of air.

An ordinary bimorph might be made to oscillate, but then you'd have a
very expensive ultrasonic cleaner. ;-P

Rich Grise gives better technical advice than John Larkin! Miracles do
happen.

32kHz crystals look like small tuning forks, and the tines vibrate the
same way

http://forums.watchuseek.com/showthread.php?t=2087

If the crystal could be persuaded to oscillate under water, the
frequency would indeed be lower than 32kHz - the mass of the water
coupled to the forks would drop the frequency, and the vicosity of the
water would lower the Q enormously.

The mass-sensing oscillators that John Larkin was talking about don't
work in water, but in gas phase environments.

I don't think the device would be much use as an an ultrasonic
cleaner. It might allow you to measure the viscosity of the water
involved, but the circuit that you'd use to do it would be tolerably
complicated.
 
S

Steve

Jan 1, 1970
0
Measuring viscocity changes of liquid solutions when needle-like
crystals begin to form is exactly what I am attempting to do with the
tuning fork. I am aware that the frequency will decrease relative to
air and Q will drop. It seems that these viscocity changes must
happen right on or at the crystal surface in order to be sensed as a
change in resonant frequency.

John - I read that 32.768 kHz crystals are typically AT cut since
those are the easiest to make. I've been using the circuit below and
changed component values in an attempt to compensate for changes in
crystal parameters when immersed in water but have not been able to
get it to oscillate in water. Maybe I'll try a higher frequency
crystal

http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem.html#ASCIISCHEM_008

Thanks for the references John. It'd be nice to make this work - a
$0.30 crystal, 4069 gate and a few capacitors and resistors is a
financially attractive alternative to a $2500 commercial instrument.

Steve
 
Measuring viscocity changes of liquid solutions when needle-like
crystals begin to form is exactly what I am attempting to do with the
tuning fork.  I am aware that the frequency will decrease relative to
air and Q will drop.  It seems that these viscocity changes must
happen right on or at the crystal surface in order to be sensed as a
change in resonant frequency.

John - I read that 32.768 kHz crystals are typically AT cut since
those are the easiest to make.  I've been using the circuit below and
changed component values in an attempt to compensate for changes in
crystal parameters when immersed in water but have not been able to
get it to oscillate in water.  Maybe I'll try a higher frequency
crystal

http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem.h...

Thanks for the references John.  It'd be nice to make this work - a
$0.30 crystal, 4069 gate and a few capacitors and resistors is a
financially attractive alternative to a $2500 commercial instrument.

Steve





- Show quoted text -

when you put the crystal in the water do you somehow insulate the
contact pads from the water?

I would think the electrical changes due to the water contacting the
contacts would be a problem... come to think of it the electrical
contact of the water to the crystal itself would be a problem...

Mark
 
S

Steve

Jan 1, 1970
0
John- from your cited reference :

"Until recently, its was believed that excessive viscous loading would
prohibit use of the QCM in liquids. In fact, operation in liquids is
indeed possible(12), and the response of the QCM is still extremely
sensitive to mass changes at the solidsolution interface. For many
years, QCMs have been used in direct contact with liquids and/or
viscoelastic films to assess changes in mass and viscoelastic
properties during chemical and electrochemical surface processes.
When the QCM comes in contact with a solution, there is a decrease in
frequency that is dependent upon the viscocity and the density of the
solution. A quantitative understanding of the resonator behavior is a
prerequisite for proper interpretation of experimental results under
total liquid immersion. This problem was first treated by Glassford
(13), and later by Kanazawa and Gordon( 14)."

12 T. Nomura and M. Okuhara, Anal. Chim. Acta 142(1982) 281.

13 A. P. M. Glassford, “Response of a Quartz Crystal Microbalance to a
liquid Deposit”, J.
Vac. Sci. Technol., 15(6)(1978) 1836

14 K. Keiji Kanazawa and Joseph Gordon II, “Frequency of a Quartz
Microbalance in
Contact with Liquid”, Anal Chem. 57(1985) 1770
K. Keiji Kanazawa and Joseph G. Gordon II, Analytica Chimica Acta,
175(1985) 99-105.


Thanks,

Steve
 
R

Rich Grise

Jan 1, 1970
0
You are in the running for the new honorary AlwaysWrong award. It
comes with a handsome engraved and signed certificate.

I know, and sometimes help, people who are doing research in quartz
microbalance instruments, and they are definitely working in water.


http://www.thinksrs.com/products/QCM200.htm

"The QCM200 uses a 5 MHz, 1" diameter, AT-cut quartz crystal wafer
with circular electrodes on both sides. Crystals are available in a
variety of materials. The crystal holder is a rugged, compact, easy to
use fixture. The holder and all crystals may be used in liquid or gas
environments."

http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/QCMTheoryapp.pdf
http://www.currentseparations.com/issues/18-3/cs18-3a.pdf

These are usually AT-cut crystals. As I said, one would have to try a
tuning-fork crystal to see what happens.

That's what I meant by "an ordinary bimorph." I read the term about
50 years ago, in a chapter about quartz crystals.

Don't hate me because I'm beautiful. ;-)

Cheers!
Rich
 
V

Vladimir Vassilevsky

Jan 1, 1970
0
John said:
I have an academic friend who is working with this stuff, using
Homeland Security money to make quartz microbalances to detect
chemical agents in solution.

From my university years, I remember the project where they used a
similar sensor to detect the alcohol content in breathing. It was pretty
sensitive and quick, however not very specific. Fun to play with, though.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
 
It is possible for the tuning fork element of a 32.768 kHz quartz
crystal to be used in an oscillator circuit if the element has been
exposed from its case and immersed in water ?  Or is its Q factor now
too low ?  The element exposed to air will produce slightly higher
frequencies than 32.768 kHz when used in a CMOS 4069 inverter gate
circuit using a 10 M ohm resistor (gate out-to-input) and 10 pF from
gate inverting input to ground.
 
It is possible for the tuning fork element of a 32.768 kHz quartz
crystal to be used in an oscillator circuit if the element has been
exposed from its case and immersed in water ?  Or is its Q factor now
too low ?  The element exposed to air will produce slightly higher
frequencies than 32.768 kHz when used in a CMOS 4069 inverter gate
circuit using a 10 M ohm resistor (gate out-to-input) and 10 pF from
gate inverting input to ground.

yes, frequency goes way down and drive went way up.

tried that in my former university days.

Steve Roberts
 
B

Bill Sloman

Jan 1, 1970
0
John Larkin said:
You are in the running for the new honorary AlwaysWrong award. It
comes with a handsome engraved and signed certificate.

I'll settle for the occcasionally partly wrong award that I can earn
I know, and sometimes help, people who are doing research in quartz
microbalance instruments, and they are definitely working in water.

Tuning fork crystals?
http://www.thinksrs.com/products/QCM200.htm

"The QCM200 uses a 5 MHz, 1" diameter, AT-cut quartz crystal wafer
with circular electrodes on both sides. Crystals are available in a
variety of materials. The crystal holder is a rugged, compact, easy to
use fixture. The holder and all crystals may be used in liquid or gas
environments."

http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/QCMTheoryapp.pdf


http://www.currentseparations.com/issues/18-3/cs18-3a.pdf


These are usually AT-cut crystals. As I said, one would have to try a
tuning-fork crystal to see what happens.

Or briefly engage one's brain.

I'd be a bit interested to see what an adsorbed monolayer would do to an
AT-cut
crystal immersed in water; as opposed to the adsorbed monolayer of water
that
you'd find if you just immersed the crystal in water.

It's nice that the QCM200 electronics can still keep the crystal oscillating
even when
it is immersed in water. It's less obvious that the oscillation frequency is
going to
change in a useful way if you dope the water (or whatever) with other
molecules.

But the ingenious people who made the electronics don't have to find a
useful
effect, they just have to supply some gear that optimistic customers can use
to
look for such a useful effect.
 
The crystal doesn't care what's obvious to you.

Nor should it. Customers are pickier.
Moron. You could google "Quartz Crystal Microbalance" and actually
learn something,

I knew what a quartz microbalance was long before there was a google
to do my searching for me.
or you can continue to be a fathead and a failure and practically accuse SRS of fraud.
But we all know which path you'll choose.

It isn't fraud to sell equipment for that meets its specification -
what the customers do with it is their business.
Stanford Research Systems has been around for a very long time - my
boss bought one of their photon counters back in 1972 - and if any of
their gear has ever set the world on fire I've yet to hear about it.
 
The technology has changed in the past 20 years. You haven't.

It doesn't sound as if the technology has changed in any interesting
way in the last twenty years. Stanford Scientific Systems may have
applied tolerably old-fashioned technology in a way that may interest
some new customers, but they don't seem to have set the world on fire.

I'd be appreciably more cheerful if I more closely ressembled the man
I was back when I was 46, but back then I was having the time of my
life, albeit on a project that was eventually cancelled, despite the
fact that it did pretty much exactly what I'd promised it would.

Since you don't know much about what I was like back then, your claim
is more than usually empty.
 
S

Steve

Jan 1, 1970
0
The guys I know (not SRS) are using shear-mode AT-cut crystals. I can
look up the guy who makes them. They won't have anything like the
coupling to liquid that a tuning fork will.
What does the crystal look like? A tuning fork crystal will _not_ be a little disk or square.

We need to measure bulk viscosity changes resulting from solution
gelation for a University research project. A crystal that is
responding to surface changes might be affected more by precipitate
effects than a tuning fork style hopefully would.
Come to think of it, perhaps at 32kHz you'd do better to just run
frequency sweeps into the crystal and analyze it's impedance directly,
instead of doing it all indirectly through an oscillator?

We want to monitor viscosity changes vs time hence the oscillator may
provide faster measurement intervals. I am not sure what time
resolution is needed nor do I know how long it might take to do the
frequency sweep if that method were used.

Steve
 
J

JosephKK

Jan 1, 1970
0
Jim said:
Jim Thompson wrote:





Measuring viscocity changes of liquid solutions when needle-like
crystals begin to form is exactly what I am attempting to do with the
tuning fork. I am aware that the frequency will decrease relative to
air and Q will drop. It seems that these viscocity changes must
happen right on or at the crystal surface in order to be sensed as a
change in resonant frequency.

John - I read that 32.768 kHz crystals are typically AT cut since
those are the easiest to make. I've been using the circuit below and
changed component values in an attempt to compensate for changes in
crystal parameters when immersed in water but have not been able to
get it to oscillate in water. Maybe I'll try a higher frequency
crystal

http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem.html#ASCIISCHEM_008


[snip]

Try reducing the 330K first. You probably don't have enough drive to
support the "load".

...Jim Thompson

I used 680K for in-case tuning fork crystals; a 330K would be
overdrive and it very likely would not oscillate.


Nonsense! I do a crystal oscillator designs every few months. Looked
to me like the "pi caps" were too small, and the drive resistor too
large.

...Jim Thompson
Those caps were specified by the manufacturers, i did not make up the
values.
The 680K was the largest value that *reliably* allowed oscillation
for 32KHz, 100KHz, 200KHz, etc tuning fork type crystals.
Blame the circuit for working contrary to your expectations...

In this case the crystal in an aqueous solution, the required drive
should be much higher.
 
M

mo12

Jan 1, 1970
0
Jim said:
Measuring viscocity changes of liquid solutions when needle-like
crystals begin to form is exactly what I am attempting to do with the
tuning fork.  I am aware that the frequency will decrease relativeto
air and Q will drop.  It seems that these viscocity changes must
happen right on or at thecrystalsurface in order to be sensed as a
change in resonant frequency.
John - I read that 32.768 kHz crystals are typically AT cut since
those are the easiest to make.  I've been using the circuit below and
changed component values in an attempt to compensate for changes in
crystalparameters when immersed in water but have not been able to
get it to oscillate in water.  Maybe I'll try a higher frequency
crystal
http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem.h...
[snip]
Try reducing the 330K first.  You probably don't have enough drive to
support the "load".
                                       ...Jim Thompson
 I used 680K for in-case tuning fork crystals; a 330K would be
overdrive and it very likely would not oscillate.
Nonsense!  I do acrystaloscillator designs every few months.  Looked
to me like the "pi caps" were too small, and the drive resistor too
large.
                                        ...Jim Thompson
  Those caps were specified by the manufacturers, i did not make up the
values.
  The 680K was the largest value that *reliably* allowed oscillation
for 32KHz, 100KHz, 200KHz, etc tuning fork type crystals.
  Blame the circuit for working contrary to your expectations...

In this case thecrystalin an aqueous solution, the required drive
should be much higher.


Seldom read Newsgroups but saw your post.
No flexure (TUNING FORK) or shear mode (at CUT) quartz crystal will
self oscillate sensibly in a fluid.
Note it is the circuit activity (I like to think of negative
resistance) not the dirve level that determine if it will "go"
However there is a crystal cut designed to alter frequency in
proportion to fluid viscosity, this is a quartz crystal rod with
electrodes placed to cause it to twist, a torsional oscillation
crystal.
I last saw a torsional quartz crystal manufactured by my employers
Marconi in the 60s
If I was to develop something today I would try to electromagnetically
generate twist in a ferrite rod or to get a rod of piezo ceramic poled
to generate a twist.
 
R

Rich Grise

Jan 1, 1970
0
Shear mode crystals oscillate just fine under water, and are the basis
for some analytical instruments. Look it up.

I have little doubt a tuning-fork crystal could be persuaded to
oscillate in water, but I don't know how useful it would be.
Wouldn't viscosity affect it?

Thanks,
Rich
 
Top