Position measurement.

[Dirk Bruere at Neopax]

Wouldn't the typical electrostatic transducer bandwidth be a couple
orders of magnitude too small?

Probably.
Maybe measure phase difference?
Anyway, I have no idea of what acoustic holography consists of and how it
differs from conventional acoustic measurement.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

 

[[email protected]]

Wouldn't the typical electrostatic transducer bandwidth be a couple
orders of magnitude too small?

That is an interesting thought. Electrostatic speakers have much
tighter coupling to air than most electric-to-acoustic transducers (and
thus a lower Q). I can't say I've ever heard of electrostatic tweeter,
but if one existed it ought to be pretty broad=band. An ion-phone
source would be even nicer, but it would be useless as a microphone -
not a problem with the continuous transmission option, of course,
though the ozone from the ion-phone speaker might chew up the area in
the long term.

 

[Jim Thompson]

Wouldn't the typical electrostatic transducer bandwidth be a couple
orders of magnitude too small?


Best regards,
Spehro Pefhany

Yep. Years ago I designed some motion detectors with 40KHz
transducers... slow as crap.

...Jim Thompson

 

[Wieslaw Bicz]

Probably.
Maybe measure phase difference?
Anyway, I have no idea of what acoustic holography consists of and how
it differs from conventional acoustic measurement.

To achieve the required accuracy, phase measurement, continuous wave and
much higher frequency, that was typically used by Polaroid is necessary.
In our vibration measurement we have achieved about =.1 micrometer
amplitude resolution and have used 200kHz transducers. In 5cm distance
even 1MHz could be used and the diplacement measurement accuracy would
be significantly higher.

W. Bicz

 

[Wieslaw Bicz]

Yep. Years ago I designed some motion detectors with 40KHz
transducers... slow as crap.

...Jim Thompson

Acoustical interferometry is working in real time, exactly as optical,
but can be significantly cheaper and easier to use.

W. Bicz

 

[Spehro Pefhany]

Yep. Years ago I designed some motion detectors with 40KHz
transducers... slow as crap.

...Jim Thompson

Some of the piezo transducers are really horrible, but it depends on
how they are made inside (the really crummy ones could be used in CW
for doppler motion detection systems). But even the more appropriate
ones ring for some time after you hit them, even if you damp them
electrically (so any signal much shorter than a wavelength is going to
get lost in the noise).

Polaroid originally used an electrostatic transducer (driven with a
transformer) for their SX-70 camera so they could use a single
transducer for send and receive. The minimum focus distance was pretty
short, maybe 16cm/6" or something like that. These ones have a
characteristic gold-plated polyester membrane visible through the
front mesh.

I've used both types- one type with an analog PID controller for
controlling the 'bubble' of hot plastic in blown-film extruders and
one type for a small microcontroller-based proximity detector. I just
bought on a whim an end-of-line parking device (IIRC similar to the
one you found a year or two ago). It uses two 40kHz piezo transducers
and an 8051 variant to measure distance and control three big
red/green/yellow LEDs. EEPROM holds the customer preset distance, I
think. Couldn't resist for $20.

 

[Jim Thompson]

On Sun, 05 Feb 2006 13:26:48 -0500, Spehro Pefhany

[snip]

I just
bought on a whim an end-of-line parking device (IIRC similar to the
one you found a year or two ago). It uses two 40kHz piezo transducers
and an 8051 variant to measure distance and control three big
red/green/yellow LEDs. EEPROM holds the customer preset distance, I
think. Couldn't resist for $20.

Where did you get it?

I tossed the Genie closers, what crap, and my new openers don't have a
convenient place to mount a magnetic switch.

I park my truck by eye, just watch for the rake handle to sway ;-)

But "N" regularly overshoots the walkway, making it a squeeze for me
to get through the door into the house.

...Jim Thompson

 

[Spehro Pefhany]

On Sun, 05 Feb 2006 13:26:48 -0500, Spehro Pefhany

[snip]

I just
bought on a whim an end-of-line parking device (IIRC similar to the
one you found a year or two ago). It uses two 40kHz piezo transducers
and an 8051 variant to measure distance and control three big
red/green/yellow LEDs. EEPROM holds the customer preset distance, I
think. Couldn't resist for $20.

Where did you get it?

Home Depot. Logix brand. I guess they didn't sell very well. I don't
know how well it works, I've only taken it apart so far ;-) , but it
looks pretty good inside design-wise, with typical low-end Chinese
assembly.

 

[Jim Thompson]

On Sun, 05 Feb 2006 13:26:48 -0500, Spehro Pefhany

[snip]

I just
bought on a whim an end-of-line parking device (IIRC similar to the
one you found a year or two ago). It uses two 40kHz piezo transducers
and an 8051 variant to measure distance and control three big
red/green/yellow LEDs. EEPROM holds the customer preset distance, I
think. Couldn't resist for $20.

Where did you get it?

Home Depot. Logix brand. I guess they didn't sell very well. I don't
know how well it works, I've only taken it apart so far ;-) , but it
looks pretty good inside design-wise, with typical low-end Chinese
assembly.

I tossed the Genie closers, what crap, and my new openers don't have a
convenient place to mount a magnetic switch.

I park my truck by eye, just watch for the rake handle to sway ;-)

But "N" regularly overshoots the walkway, making it a squeeze for me
to get through the door into the house.

...Jim Thompson

Found a similar product called Park Zone at http://www.intheswim.com
.... $29.99 with A/C adapter.

...Jim Thompson

 

[Jim Thompson]

On Sun, 05 Feb 2006 12:15:40 -0700, the renowned Jim Thompson

On Sun, 05 Feb 2006 13:26:48 -0500, Spehro Pefhany

[snip]

I just
bought on a whim an end-of-line parking device (IIRC similar to the
one you found a year or two ago). It uses two 40kHz piezo transducers
and an 8051 variant to measure distance and control three big
red/green/yellow LEDs. EEPROM holds the customer preset distance, I
think. Couldn't resist for $20.

Where did you get it?

Home Depot. Logix brand. I guess they didn't sell very well. I don't
know how well it works, I've only taken it apart so far ;-) , but it
looks pretty good inside design-wise, with typical low-end Chinese
assembly.

I tossed the Genie closers, what crap, and my new openers don't have a
convenient place to mount a magnetic switch.

I park my truck by eye, just watch for the rake handle to sway ;-)

But "N" regularly overshoots the walkway, making it a squeeze for me
to get through the door into the house.

...Jim Thompson

Found a similar product called Park Zone at http://www.intheswim.com
... $29.99 with A/C adapter.

...Jim Thompson

Single transducer system rather than dual, other than that, it's
pretty similar, although my one didn't come with an AC adapter.

I don't shop Home Depot. They conned me ONCE.

...Jim Thompson

 

[Spehro Pefhany]

On Sun, 05 Feb 2006 13:26:48 -0500, Spehro Pefhany

[snip]

I just
bought on a whim an end-of-line parking device (IIRC similar to the
one you found a year or two ago). It uses two 40kHz piezo transducers
and an 8051 variant to measure distance and control three big
red/green/yellow LEDs. EEPROM holds the customer preset distance, I
think. Couldn't resist for $20.

Where did you get it?

Home Depot. Logix brand. I guess they didn't sell very well. I don't
know how well it works, I've only taken it apart so far ;-) , but it
looks pretty good inside design-wise, with typical low-end Chinese
assembly.

I tossed the Genie closers, what crap, and my new openers don't have a
convenient place to mount a magnetic switch.

I park my truck by eye, just watch for the rake handle to sway ;-)

But "N" regularly overshoots the walkway, making it a squeeze for me
to get through the door into the house.

...Jim Thompson

Found a similar product called Park Zone at http://www.intheswim.com
... $29.99 with A/C adapter.

...Jim Thompson

Single transducer system rather than dual, other than that, it's
pretty similar, although my one didn't come with an AC adapter.

 

[Spehro Pefhany]

I don't shop Home Depot. They conned me ONCE.

...Jim Thompson

What's the story on that? I find them okay, though their handling of
returns could be much better (faster, mostly). They, and their ilk,
have driven most of the small competent hardware stores out of
business.

One of the reviews on the system you mention says that, contrary to
claims, the instructions say 18" is the minimum working distance, and
in fact it needs that much room. It also needs space on all sides or
it picks up false echos, and it doesn't work too well with curved
bumpers, according to them.


Best regards,
Spehro Pefhany

 

[Michael A. Terrell]

What's the story on that? I find them okay, though their handling of
returns could be much better (faster, mostly). They, and their ilk,
have driven most of the small competent hardware stores out of
business.

There weren't any real hardware stores around when the built near me.
Sure they could order things if you could wait, or you didn't mind
paying $12 for a $3 part. Real hardware stores started disappearing in
the '70s, long before HD opened their first store. less people were
doing their own repairs, and big contractors had salespeople calling on
them and delivering things right to the jobsite for them. I saw several
close in the '70s that had opened in the late 1800s, and had been family
owned businesses, till there was no one left who wanted to run the
store. Lose that connection to the store's past and most people went
elsewhere.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Rich Grise]

Spehro Pefhany wrote:

That is an interesting thought. Electrostatic speakers have much tighter
coupling to air than most electric-to-acoustic transducers (and thus a
lower Q). I can't say I've ever heard of electrostatic tweeter, ...

Huh?

http://www.google.com/search?hl=en&q="electrostatic+tweeter"

Cheers!
Rich