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Thread
2009-05-11 by Muhammad Amiruddin
Dear all,
please help me,
i want make project for measuring the level of water on the tank that approximately 15 m high. what senssor that i should use ?
Is there any ultrasonic senssor wich can measure range until 15 m ?
rgds,
4mir
[Non-text portions of this message have been removed]2009-05-11 by Jim Wagner
On May 10, 2009, at 7:39 PM, Muhammad Amiruddin wrote: > > > Dear all, > > please help me, > > i want make project for measuring the level of water on the tank > that approximately 15 m high. what senssor that i should use ? > > Is there any ultrasonic senssor wich can measure range until 15 m ? > > rgds, > > 4mir > > > [Non-text portions of this message have been removed] > > > Maxbotics ultasonics have a range of 256 inches or 21' or about 7m. Not many have much greater range than that. Jim Wagner Oregon Research Electronics [Non-text portions of this message have been removed]
2009-05-11 by Muhammad Amiruddin
Is there any other sensor that can measure range over than 15 m? --- On Mon, 5/11/09, Jim Wagner <wagnerj@proaxis.com> wrote:
From: Jim Wagner <wagnerj@proaxis.com>
Subject: Re: [AVR-Chat] (unknown)
To: AVR-Chat@yahoogroups.com
Date: Monday, May 11, 2009, 2:43 AM
On May 10, 2009, at 7:39 PM, Muhammad Amiruddin wrote:
>
>
> Dear all,
>
> please help me,
>
> i want make project for measuring the level of water on the tank
> that approximately 15 m high. what senssor that i should use ?
>
> Is there any ultrasonic senssor wich can measure range until 15 m ?
>
> rgds,
>
> 4mir
>
>
> [Non-text portions of this message have been removed]
>
>
>
Maxbotics ultasonics have a range of 256 inches or 21' or about 7m.
Not many have much greater range than that.
Jim Wagner
Oregon Research Electronics
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]2009-05-11 by Robert Adsett
Muhammad Amiruddin wrote: > Is there any other sensor that can measure range over than 15 m? Float Pressure/Weight Radar Conduction Optical should be possible too Robert -- http://www.aeolusdevelopment.com/ From the Divided by a Common Language File (Edited to protect the guilty) ME - "I'd like to get Price and delivery for connector Part # XXXXX" Dist./Rep - "$X.XX Lead time 37 days" ME - "Anything we can do about lead time? 37 days seems a bit high." Dist./Rep - "that is the lead time given because our stock is live.... we currently have stock."
2009-05-11 by Robert Tilden
http://www.apgsensors.com/ultrasonic-sensor/dcu-1100.html ----------------------------------- Bob Tilden, tilden@northwestern.edu High Energy Physics Group Northwestern University
-----Original Message----- From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf Of Robert Adsett Sent: Sunday, May 10, 2009 10:38 PM To: AVR-Chat@yahoogroups.com Subject: Re: [AVR-Chat] (unknown) Muhammad Amiruddin wrote: > Is there any other sensor that can measure range over than 15 m? Float Pressure/Weight Radar Conduction Optical should be possible too Robert -- http://www.aeolusdevelopment.com/ From the Divided by a Common Language File (Edited to protect the guilty) ME - "I'd like to get Price and delivery for connector Part # XXXXX" Dist./Rep - "$X.XX Lead time 37 days" ME - "Anything we can do about lead time? 37 days seems a bit high." Dist./Rep - "that is the lead time given because our stock is live.... we currently have stock." ------------------------------------ Yahoo! Groups Links
2009-05-13 by Brian
I think the best non-movement sensor would be a presure sensor at the bottom of the tank. No moving parts and it can be sealed. So it could measure many liquids. Brian --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin <amiruddin.muhammad@...> wrote:
> > Dear all, > > please help me, > > i want make project for measuring the level of water on the tank that approximately 15 m high. what senssor that i should use ? > > Is there any ultrasonic senssor wich can measure range until 15 m ? > > rgds, > > 4mir > > > > > > [Non-text portions of this message have been removed] >
2009-05-13 by Philippe Habib
I have seen ultrasonic sensors that do what you want if you can't add a pressure sensor at the bottom.
On May 12, 2009, at 7:09 PM, Brian wrote: > I think the best non-movement sensor would be a presure sensor at > the bottom of the tank. No moving parts and it can be sealed. So it > could measure many liquids. > > Brian > > --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin > <amiruddin.muhammad@...> wrote: >> >> Dear all, >> >> please help me, >> >> i want make project for measuring the level of water on the tank >> that approximately 15 m high. what senssor that i should use ? >> >> Is there any ultrasonic senssor wich can measure range until 15 m ? >> >> rgds, >> >> 4mir >> >> >> >> >> >> [Non-text portions of this message have been removed] >> > > > > > ------------------------------------ > > Yahoo! Groups Links > > >
2009-05-13 by Muhammad Amiruddin
thanks for all you --- On Mon, 5/11/09, Muhammad Amiruddin <amiruddin.muhammad@yahoo.com> wrote:
From: Muhammad Amiruddin <amiruddin.muhammad@yahoo.com>
Subject: Re: [AVR-Chat] (unknown)
To: AVR-Chat@yahoogroups.com
Date: Monday, May 11, 2009, 3:10 AM
Is there any other sensor that can measure range over than 15 m?
--- On Mon, 5/11/09, Jim Wagner <wagnerj@proaxis. com> wrote:
From: Jim Wagner <wagnerj@proaxis. com>
Subject: Re: [AVR-Chat] (unknown)
To: AVR-Chat@yahoogroup s.com
Date: Monday, May 11, 2009, 2:43 AM
On May 10, 2009, at 7:39 PM, Muhammad Amiruddin wrote:
>
>
> Dear all,
>
> please help me,
>
> i want make project for measuring the level of water on the tank
> that approximately 15 m high. what senssor that i should use ?
>
> Is there any ultrasonic senssor wich can measure range until 15 m ?
>
> rgds,
>
> 4mir
>
>
> [Non-text portions of this message have been removed]
>
>
>
Maxbotics ultasonics have a range of 256 inches or 21' or about 7m.
Not many have much greater range than that.
Jim Wagner
Oregon Research Electronics
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]2009-05-13 by Bruce Parham
I like the method used in most washing machines where they place a pressure sensor above the liquid and run an open ended tube down to the bottom. That keeps the sensor and electronics dry. Given that water pressure = 1.363 PSI/m, a 15 m water head will produce 1.363 PSI/m x 15 m = 20.45 PSI. A 25 to 30 PSI full scale sensor should do the trick. Bruce
>> I think the best non-movement sensor would be a presure sensor at >> the bottom of the tank. No moving parts and it can be sealed. So it >> could measure many liquids. >> >> Brian >> >> --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin >> <amiruddin.muhammad@...> wrote: >>> Dear all, >>> >>> please help me, >>> >>> i want make project for measuring the level of water on the tank >>> that approximately 15 m high. what senssor that i should use ? >>> >>> Is there any ultrasonic senssor wich can measure range until 15 m ? >>> >>> rgds, >>> >>> 4mir
2009-05-13 by David Kelly
On Wed, May 13, 2009 at 08:09:32AM -0700, Bruce Parham wrote: > > Given that water pressure = 1.363 PSI/m, a 15 m water head will > produce 1.363 PSI/m x 15 m = 20.45 PSI. A 25 to 30 PSI full scale > sensor should do the trick. I haven't fielded water pressure sensors but I'd seriously consider a 50 psi full scale sensor for that application because water has inertia and can pound the sensor if everything is not nice and calm. At the very least study the maximum pressure the sensor can be exposed in addition to its full scale range. -- David Kelly N4HHE, dkelly@HiWAAY.net ======================================================================== Whom computers would destroy, they must first drive mad.
2009-05-13 by David VanHorn
> At the very least study the maximum pressure the sensor can be exposed > in addition to its full scale range. A very good idea.. Water does not compress, but your sensor does. "what was that crunching sound?" -- There is no computer problem which cannot be solved by proper application of a sufficiently large hammer.
2009-05-13 by Philippe Habib
I worked on a lab device that used this system and water droplets still found their way into the sensor and toasted it. The solution was an expensive custom gauge protector. So if you use this approach, you need to be sure the mechanical stuff is 100% taken care of properly.
On May 13, 2009, at 8:09 AM, Bruce Parham wrote: > I like the method used in most washing machines where they place a > pressure > sensor above the liquid and run an open ended tube down to the > bottom. That > keeps the sensor and electronics dry. > > Given that water pressure = 1.363 PSI/m, a 15 m water head will > produce > 1.363 PSI/m x 15 m = 20.45 PSI. A 25 to 30 PSI full scale sensor > should do > the trick. > > Bruce > > >>> I think the best non-movement sensor would be a presure sensor at >>> the bottom of the tank. No moving parts and it can be sealed. So it >>> could measure many liquids. >>> >>> Brian >>> >>> --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin >>> <amiruddin.muhammad@...> wrote: >>>> Dear all, >>>> >>>> please help me, >>>> >>>> i want make project for measuring the level of water on the tank >>>> that approximately 15 m high. what senssor that i should use ? >>>> >>>> Is there any ultrasonic senssor wich can measure range until 15 m ? >>>> >>>> rgds, >>>> >>>> 4mir > > > ------------------------------------ > > Yahoo! Groups Links > > >
2009-05-13 by Bruce Parham
Sorry, my earlier response was incomplete, just the germ of an idea. Since the inverted standpipe is initially filled with air, when the liquid level rises, the gas will be compressed allowing liquid to enter the tube which will reduce the pressure head. The actual pressure measured will depend on the total volume of the tube and the amount displace by liquid but will always be less than the pressure at the bottom of the tube. -- The gas compression correction is left as an exercise for the student. -- Bruce David VanHorn wrote:
>> At the very least study the maximum pressure the sensor can be exposed >> in addition to its full scale range. > > A very good idea.. Water does not compress, but your sensor does. > "what was that crunching sound?" >
2009-05-13 by David VanHorn
If you need to keep the liquid out, you can use a diaphram. The diaphram flexes and passes the pressure change, but you could fill the backside with dry nitrogen. -- There is no computer problem which cannot be solved by proper application of a sufficiently large hammer.
2009-05-13 by David Kelly
On Wed, May 13, 2009 at 09:47:39AM -0700, Bruce Parham wrote: > Sorry, my earlier response was incomplete, just the germ of an idea. > > Since the inverted standpipe is initially filled with air, when the > liquid level rises, the gas will be compressed allowing liquid to > enter the tube which will reduce the pressure head. The actual > pressure measured will depend on the total volume of the tube and the > amount displace by liquid but will always be less than the pressure at > the bottom of the tube. > > -- The gas compression correction is left as an exercise for the > student. -- All to avoid purchase of a sensor which won't be damaged by the liquid? The compressed air in the inverted standpipe will eventually dissolve into the liquid. This proposed solution will not work in a static situation, must be cyclical allowing the air in the standpipe be refreshed periodically. -- David Kelly N4HHE, dkelly@HiWAAY.net ======================================================================== Whom computers would destroy, they must first drive mad.
2009-05-13 by David VanHorn
> All to avoid purchase of a sensor which won't be damaged by the liquid? > > The compressed air in the inverted standpipe will eventually dissolve > into the liquid. This proposed solution will not work in a static > situation, must be cyclical allowing the air in the standpipe be > refreshed periodically. Valid points.. I'd once proposed stream level monitoring by using a roller pump to smoothly push air into a pipe that was anchored to the bottom. The idea being that the continuous flow of air keeps the pipe clear of cruft, and is pretty benign to the sensor. You have to subtract outside air pressure, but that's just one more sensor that we needed anyway. -- There is no computer problem which cannot be solved by proper application of a sufficiently large hammer.
2009-05-13 by Ken Holt
My water pressure sensor has only failed due to freezing of the water. My house fresh water tank is only 4' tall, and not quite cylindrical, so the pressure reading is not quite linear with volume. I use a DVM always-on to read millivolts: 100mv empty, 500 mv full. The major problem has been variation with atmospheric pressure, which was only improved slightly by changing the sensor from gage to differential. Philippe Habib wrote:
> > > I worked on a lab device that used this system and water droplets > still found their way into the sensor and toasted it. The solution > was an expensive custom gauge protector. So if you use this approach, > you need to be sure the mechanical stuff is 100% taken care of properly. > > On May 13, 2009, at 8:09 AM, Bruce Parham wrote: > > > I like the method used in most washing machines where they place a > > pressure > > sensor above the liquid and run an open ended tube down to the > > bottom. That > > keeps the sensor and electronics dry. > > > > Given that water pressure = 1.363 PSI/m, a 15 m water head will > > produce > > 1.363 PSI/m x 15 m = 20.45 PSI. A 25 to 30 PSI full scale sensor > > should do > > the trick. > > > > Bruce > > > > > >>> I think the best non-movement sensor would be a presure sensor at > >>> the bottom of the tank. No moving parts and it can be sealed. So it > >>> could measure many liquids. > >>> > >>> Brian > >>> > >>> --- In AVR-Chat@yahoogroups.com > <mailto:AVR-Chat%40yahoogroups.com>, Muhammad Amiruddin > >>> <amiruddin.muhammad@...> wrote: > >>>> Dear all, > >>>> > >>>> please help me, > >>>> > >>>> i want make project for measuring the level of water on the tank > >>>> that approximately 15 m high. what senssor that i should use ? > >>>> > >>>> Is there any ultrasonic senssor wich can measure range until 15 m ? > >>>> > >>>> rgds, > >>>> > >>>> 4mir > > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > > > > >
2009-05-13 by kernels_nz
Back when I was at Uni a few years ago, one of the students had a project to electronically measure the water level in a plastic tank. Best way I have seen this done is run two parallel metal plates along the depth of the tank and then look at the change in capacitance between the two plates based on the amount of water between the plates. As the water level dropped, the capacitance would decrease because the relative permeability of water is higher than air . . . (Hope I remembered all this correctly) Set this up as a oscillator with frequency based on capacitance and you have a varying output frequency based on the water level. Hein B Auckland, New Zealand. --- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@...> wrote:
> > I think the best non-movement sensor would be a presure sensor at the bottom of the tank. No moving parts and it can be sealed. So it could measure many liquids. > > Brian > > --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin <amiruddin.muhammad@> wrote: > > > > Dear all, > > > > please help me, > > > > i want make project for measuring the level of water on the tank that approximately 15 m high. what senssor that i should use ? > > > > Is there any ultrasonic senssor wich can measure range until 15 m ? > > > > rgds, > > > > 4mir > > > > > > > > > > > > [Non-text portions of this message have been removed] > > >
2009-05-14 by Robert Tilden
Besides the ultrasonic sensor there are a number of other methods... A donut shaped float incorporating a magnet which rides up and down around a magnetostrictive line. One sends a pulse down the line and measures the return from the magnetic float location. Very accurate. A donut shaped float incorporating a magnet which rides up and down a track with embedded reed switches. As has been mentioned, a capacitive strip line. A weighted float attached to a counterweighted (or spring loaded) cable which turns an encoder as the float travels up and down. Also very accurate. Similar to the capacitive sensor, a resistive sensor (for conductive fluids). The higher the level, the less the resistance. An air bubbler. Sense the pressure of the air line while slowly bubbling said line at the bottom of the tank. The sensor could be above the liquid level so as not to be harmed by a pressure failure. Etc... ----------------------------------- Bob Tilden, tilden@northwestern.edu High Energy Physics Group Northwestern University
-----Original Message----- From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf Of kernels_nz Sent: Wednesday, May 13, 2009 7:33 PM To: AVR-Chat@yahoogroups.com Subject: [AVR-Chat] Re: Sensor Back when I was at Uni a few years ago, one of the students had a project to electronically measure the water level in a plastic tank. Best way I have seen this done is run two parallel metal plates along the depth of the tank and then look at the change in capacitance between the two plates based on the amount of water between the plates. As the water level dropped, the capacitance would decrease because the relative permeability of water is higher than air . . . (Hope I remembered all this correctly) Set this up as a oscillator with frequency based on capacitance and you have a varying output frequency based on the water level. Hein B Auckland, New Zealand. --- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@...> wrote: > > I think the best non-movement sensor would be a presure sensor at the bottom of the tank. No moving parts and it can be sealed. So it could measure many liquids. > > Brian > > --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin <amiruddin.muhammad@> wrote: > > > > Dear all, > > > > please help me, > > > > i want make project for measuring the level of water on the tank that approximately 15 m high. what senssor that i should use ? > > > > Is there any ultrasonic senssor wich can measure range until 15 m ? > > > > rgds, > > > > 4mir > > > > > > > > > > > > [Non-text portions of this message have been removed] > > > ------------------------------------ Yahoo! Groups Links
2009-05-14 by Julian Higginson
I've been looking at VEGA stuff lately for liquid level detection purposes. http://www.vega.com/au/Level_measurement_ultrasonic_VEGASON63.htm this does what you want.... just.... It is a loop powered 4-20mA acoustic probe, and so you just sit it above the water, and then give it 24V on its positive terminal, then run its negative terminal into a 100R resistor to system ground, which will give you a voltage range of 0.4V to 2V you can measure with an ADC... Or you could implement a serial-HART modem and you can query it via HART, and even setup its parameters from your application, too. But really, for measuring 15m, you have a LOT more choice if you go radar. And a lot more ability to measure greater range if needed. These probes are also 4-20mA loop powered devices, so power consumption will be the same... http://www.vega.com/au/Level_measurement_radar_VEGAPULS62.htm
-----Original Message-----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Muhammad Amiruddin
Sent: Monday, 11 May 2009 12:39 PM
To: AVR-Chat@yahoogroups.com
Subject: [AVR-Chat] (unknown)
Dear all,
please help me,
i want make project for measuring the level of water on the tank that
approximately 15 m high. what senssor that i should use ?
Is there any ultrasonic senssor wich can measure range until 15 m ?
rgds,
4mir
[Non-text portions of this message have been removed]
------------------------------------
Yahoo! Groups Links2009-05-14 by Jim Wagner
Campbell Scientific makes a "bubbler" to measure water depth. They get a good price for it, also. Jim Wagner Oregon Research Electronics On May 13, 2009, at 6:41 PM, Robert Tilden wrote: > > > Besides the ultrasonic sensor there are a number of other methods.. > > A donut shaped float incorporating a magnet which rides up and down > around a > magnetostrictive line. One sends a pulse down the line and measures > the > return from the magnetic float location. Very accurate. > > A donut shaped float incorporating a magnet which rides up and down > a track > with embedded reed switches. > > As has been mentioned, a capacitive strip line. > > A weighted float attached to a counterweighted (or spring loaded) > cable > which turns an encoder as the float travels up and down. Also very > accurate > > Similar to the capacitive sensor, a resistive sensor (for conductive > fluids). The higher the level, the less the resistance. > > An air bubbler. Sense the pressure of the air line while slowly > bubbling > said line at the bottom of the tank. The sensor could be above the > liquid > level so as not to be harmed by a pressure failure. > > Etc... > > ----------------------------------- > Bob Tilden, tilden@northwestern.edu > High Energy Physics Group > Northwestern University > > -----Original Message----- > From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On > Behalf > Of kernels_nz > Sent: Wednesday, May 13, 2009 7:33 PM > To: AVR-Chat@yahoogroupscom > Subject: [AVR-Chat] Re: Sensor > > Back when I was at Uni a few years ago, one of the students had a > project to > electronically measure the water level in a plastic tank. Best way I > have > seen this done is run two parallel metal plates along the depth of > the tank > and then look at the change in capacitance between the two plates > based on > the amount of water between the plates. As the water level dropped, > the > capacitance would decrease because the relative permeability of > water is > higher than air . . . (Hope I remembered all this correctly) Set > this up as > a oscillator with frequency based on capacitance and you have a > varying > output frequency based on the water level. > > Hein B > Auckland, New Zealand. > > --- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@...> wrote: > > > > I think the best non-movement sensor would be a presure sensor at > the > bottom of the tank. No moving parts and it can be sealed. So it could > measure many liquids. > > > > Brian > > > > --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin > <amiruddin.muhammad@> > wrote: > > > > > > Dear all, > > > > > > please help me, > > > > > > i want make project for measuring the level of water on the tank > that > approximately 15 m high. what senssor that i should use ? > > > > > > Is there any ultrasonic senssor wich can measure range until 15 > m ? > > > > > > rgds, > > > > > > 4mir > > > > > > > > > > > > > > > > > > [Non-text portions of this message have been removed] > > > > > > > ------------------------------------ > > Yahoo! Groups Links > > > [Non-text portions of this message have been removed]
2009-05-14 by Brian
I think I may have an idea. a pressure sensor at the top of the tank and a rod extending down into the tank with a plastic ball fixed at the end. the higher the water level the more force on the sensor. Brian --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin <amiruddin.muhammad@...> wrote:
> > Dear all, > > please help me, > > i want make project for measuring the level of water on the tank that approximately 15 m high. what senssor that i should use ? > > Is there any ultrasonic senssor wich can measure range until 15 m ? > > rgds, > > 4mir > > > > > > [Non-text portions of this message have been removed] >
2009-05-14 by Brian
Jameco has this http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=129120& you could interface it with a microcontroller and obtain almost any distance within reason. Brian --- In AVR-Chat@yahoogroups.com, wagnerj@... wrote:
> > This might work for small depth changes, such as trying to hold a water > level constant. But, I would not bet anything on having it work over a 15 > meter range. > > Jim Wagner > Oregon Research Electronics > > > How about this? > > A water tight ball with a magnet in it. A magnetic field sensor at the > > top of the tank. The higher the fluid level, the more mag field sensed. > > Use a permeable tube to hold the floating ball so that it stays > > more-or-less in one area. A magnetic sensor sensitive enough for this to > > work might be pricey though. This is a kind of fancy way to do the force > > sensor you suggested with no moving parts but a floating ball. :) > > > > DLC > > > >> I think I may have an idea. a pressure sensor at the top of the tank and > >> a > >> rod extending down into the tank with a plastic ball fixed at the end. > >> the > >> higher the water level the more force on the sensor. > >> > >> Brian > >> > >> --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin > >> <amiruddin.muhammad@> wrote: > >>> > >>> Dear all, > >>> > >>> please help me, > >>> > >>> i want make project for measuring the level of water on the tank that > >>> approximately 15 m high. what senssor that i should use ? > >>> > >>> Is there any ultrasonic senssor wich can measure range until 15 m ? > >>> > >>> rgds, > >>> > >>> 4mir > >>> > >>> > >>> > >>> > >>> > >>> [Non-text portions of this message have been removed] > >>> > >> > >> > >> > >> > >> ------------------------------------ > >> > >> Yahoo! Groups Links > >> > >> > >> > >> > > > > > > -- > > Dennis Clark > > TTT Enterprises > > > > >
2009-05-14 by Graham Davies
--- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@...> wrote: > > ... a pressure sensor at the top > of the tank and a rod extending > down into the tank with a plastic > ball fixed at the end. the higher > the water level the more force on > the sensor. Are you suggesting that the force of buoyancy on the plastic ball will increase as the water level increases? You might want to have a word with Archimedes about that. Graham.
2009-05-14 by Dennis Clark
How about this? A water tight ball with a magnet in it. A magnetic field sensor at the top of the tank. The higher the fluid level, the more mag field sensed. Use a permeable tube to hold the floating ball so that it stays more-or-less in one area. A magnetic sensor sensitive enough for this to work might be pricey though. This is a kind of fancy way to do the force sensor you suggested with no moving parts but a floating ball. :) DLC > I think I may have an idea. a pressure sensor at the top of the tank and a > rod extending down into the tank with a plastic ball fixed at the end. the > higher the water level the more force on the sensor. > > Brian > > --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin > <amiruddin.muhammad@...> wrote: >> >> Dear all, >> >> please help me, >> >> i want make project for measuring the level of water on the tank that >> approximately 15 m high. what senssor that i should use ? >> >> Is there any ultrasonic senssor wich can measure range until 15 m ? >> >> rgds, >> >> 4mir >> >> >> >> >> >> [Non-text portions of this message have been removed] >> > > > > > ------------------------------------ > > Yahoo! Groups Links > > > > -- Dennis Clark TTT Enterprises
2009-05-14 by Brian
This is true if you use the device as is but.... using only the sensor module, not using the control board, and a micro you should be able to extend the range. Thinking this is an AVR group it may be dooable. As for me I would have to modify it. Couldnt resist, the only thing I was conserned about was minimum distance. Brian --- In AVR-Chat@yahoogroups.com, Jim Wagner <wagnerj@...> wrote:
> > Detection range is only 1.5m. OP asks for 15m. > > Jim Wagner > Oregon Research Electronics
2009-05-14 by wagnerj@proaxis.com
This might work for small depth changes, such as trying to hold a water level constant. But, I would not bet anything on having it work over a 15 meter range. Jim Wagner Oregon Research Electronics
> How about this? > A water tight ball with a magnet in it. A magnetic field sensor at the > top of the tank. The higher the fluid level, the more mag field sensed. > Use a permeable tube to hold the floating ball so that it stays > more-or-less in one area. A magnetic sensor sensitive enough for this to > work might be pricey though. This is a kind of fancy way to do the force > sensor you suggested with no moving parts but a floating ball. :) > > DLC > >> I think I may have an idea. a pressure sensor at the top of the tank and >> a >> rod extending down into the tank with a plastic ball fixed at the end. >> the >> higher the water level the more force on the sensor. >> >> Brian >> >> --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin >> <amiruddin.muhammad@...> wrote: >>> >>> Dear all, >>> >>> please help me, >>> >>> i want make project for measuring the level of water on the tank that >>> approximately 15 m high. what senssor that i should use ? >>> >>> Is there any ultrasonic senssor wich can measure range until 15 m ? >>> >>> rgds, >>> >>> 4mir >>> >>> >>> >>> >>> >>> [Non-text portions of this message have been removed] >>> >> >> >> >> >> ------------------------------------ >> >> Yahoo! Groups Links >> >> >> >> > > > -- > Dennis Clark > TTT Enterprises > >
2009-05-14 by Brian
From what I know, as the water level rises the pressure at the bottom increases causing more of an uplift of an object held at the bottom. Brian
> > Are you suggesting that the force of buoyancy on the plastic ball will increase as the water level increases? You might want to have a word with Archimedes about that. > > Graham. >
2009-05-14 by Brian
There is a user manual at: http://www.jameco.com/Jameco/Products/ProdDS/129120MAN.pdf It also has a schmatic to help interface it. Brian --- In AVR-Chat@yahoogroups.com, "Alex Shepherd" <lists06@...> wrote:
> > > Detection range is only 1.5m. OP asks for 15m. > > I was considering one of these: > > http://www.sparkfun.com/commerce/product_info.php?products_id=9009 > > For my water tanks but they are completely buried so could get flooded in a > storm so I might try the: > > measuring the upwards force exerted by a float at the bottom of a > long pole held vertical idea. > > Regards > > Alex Shepherd >
2009-05-15 by Jim Wagner
Detection range is only 1.5m. OP asks for 15m. Jim Wagner Oregon Research Electronics On May 14, 2009, at 4:49 PM, Brian wrote: > > > Jameco has this > > http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=129120& > > you could interface it with a microcontroller and obtain almost any > distance within reason. > > Brian > > --- In AVR-Chat@yahoogroups.com, wagnerj@... wrote: > > > > This might work for small depth changes, such as trying to hold a > water > > level constant. But, I would not bet anything on having it work > over a 15 > > meter range. > > > > Jim Wagner > > Oregon Research Electronics > > > > > How about this? > > > A water tight ball with a magnet in it. A magnetic field sensor > at the > > > top of the tank. The higher the fluid level, the more mag field > sensed. > > > Use a permeable tube to hold the floating ball so that it stays > > > more-or-less in one area. A magnetic sensor sensitive enough for > this to > > > work might be pricey though. This is a kind of fancy way to do > the force > > > sensor you suggested with no moving parts but a floating ball. :) > > > > > > DLC > > > > > >> I think I may have an idea. a pressure sensor at the top of the > tank and > > >> a > > >> rod extending down into the tank with a plastic ball fixed at > the end. > > >> the > > >> higher the water level the more force on the sensor. > > >> > > >> Brian > > >> > > >> --- In AVR-Chat@yahoogroups.com, Muhammad Amiruddin > > >> <amiruddin.muhammad@> wrote: > > >>> > > >>> Dear all, > > >>> > > >>> please help me, > > >>> > > >>> i want make project for measuring the level of water on the > tank that > > >>> approximately 15 m high. what senssor that i should use ? > > >>> > > >>> Is there any ultrasonic senssor wich can measure range until > 15 m ? > > >>> > > >>> rgds, > > >>> > > >>> 4mir > > >>> > > >>> > > >>> > > >>> > > >>> > > >>> [Non-text portions of this message have been removed] > > >>> > > >> > > >> > > >> > > >> > > >> ------------------------------------ > > >> > > >> Yahoo! Groups Links > > >> > > >> > > >> > > >> > > > > > > > > > -- > > > Dennis Clark > > > TTT Enterprises > > > > > > > > > > > [Non-text portions of this message have been removed]
2009-05-15 by Jim Wagner
But water density increases with depth, and thus apparent buoyancy increases as the water gets deeper. Jim Wagner Oregon Research Electronics On May 14, 2009, at 5:28 PM, Graham Davies wrote: > > > --- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@...> wrote: > > > > ... a pressure sensor at the top > > of the tank and a rod extending > > down into the tank with a plastic > > ball fixed at the end. the higher > > the water level the more force on > > the sensor. > > Are you suggesting that the force of buoyancy on the plastic ball > will increase as the water level increases? You might want to have a > word with Archimedes about that. > > Graham. > > > [Non-text portions of this message have been removed]
2009-05-15 by Alex Shepherd
> Detection range is only 1.5m. OP asks for 15m. I was considering one of these: http://www.sparkfun.com/commerce/product_info.php?products_id=9009 For my water tanks but they are completely buried so could get flooded in a storm so I might try the: measuring the upwards force exerted by a float at the bottom of a long pole held vertical idea. Regards Alex Shepherd
2009-05-15 by Roy E. Burrage
I've lost the original post about this application, but we've had to use level sensors here a good bit. Capacitive sensors will be very temperature sensitive. This is not just a function of capacitor plate physical issues, but the vapor in the vessel. Vapor in the vessel will also have an affect on ultrasonic and radio/radar type level sensors so the vessel temperature is going to be an issue. A float switch will be subject to issues of fluid condition. If there's a chance the fluid may have oil, pond scum, or other types of scuzz in it, there's a possibility that this stuff will build up on the float and eventually cause it to fail. It will also be subject to problems if there's too much turbulence. The float can get damaged. A pair of pressure switches can also be used in a window comparator, but with a bubbler configuration. Run a tube down in the vessel to the desired depths. Run some low pressure air in the tubes. Set the top level switch to come on when the fluid level reaches that high, perhaps to turn off a feed pump or turn off a purge pump. Set the lower switch to operate when the level goes below its tube end, perhaps to turn on a fill pump. So with this configuration a pump would come on until the level inside the vessel reaches the tube for the top pressure switch then turn off when the switch operates. The pump will stay off until the fluid level goes below the end of the lower switch's tube, and then turn on again when it does. The the cycle repeats. These switches can be had for about 15 bucks each, with teflon diaphragms. The pressure source could be something as simple as a 10 dollar aquarium aerator pump. For a one-off application, is the original poster spending 500 bucks to find a 50 cent solution to a 75 dollar problem? If we put a value on time, it could very well be much more economical to buy a 100 dollar temperature compensated pressure transducer mounted in the side of the vessel toward the bottom. That would easily buy a stainless steel wetted parts transducer. It wouldn't be accurate to 0.0025% of reading, but it would be plenty accurate for production purposes. REB David Kelly wrote: > On Wed, May 13, 2009 at 09:47:39AM -0700, Bruce Parham wrote: > >> Sorry, my earlier response was incomplete, just the germ of an idea. >> >> Since the inverted standpipe is initially filled with air, when the >> liquid level rises, the gas will be compressed allowing liquid to >> enter the tube which will reduce the pressure head. The actual >> pressure measured will depend on the total volume of the tube and the >> amount displace by liquid but will always be less than the pressure at >> the bottom of the tube. >> >> -- The gas compression correction is left as an exercise for the >> student. -- >> > > All to avoid purchase of a sensor which won't be damaged by the liquid? > > The compressed air in the inverted standpipe will eventually dissolve > into the liquid. This proposed solution will not work in a static > situation, must be cyclical allowing the air in the standpipe be > refreshed periodically. > [Non-text portions of this message have been removed]
2009-05-15 by dlc
Ahem, Water density is a constant, water _pressure_ increases with depth, and if the ball acts the way my BC does, the air in the plastic ball loses buoyancy as the water depth increases. But since my BC compresses with depth and the plastic ball probably wouldn't, that might not be so. These are basics every diver learns. DLC Jim Wagner wrote: > But water density increases with depth, and thus apparent buoyancy > increases as the water gets deeper. > > Jim Wagner > Oregon Research Electronics > > On May 14, 2009, at 5:28 PM, Graham Davies wrote: > >> >> --- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@...> wrote: >>> ... a pressure sensor at the top >>> of the tank and a rod extending >>> down into the tank with a plastic >>> ball fixed at the end. the higher >>> the water level the more force on >>> the sensor. >> Are you suggesting that the force of buoyancy on the plastic ball >> will increase as the water level increases? You might want to have a >> word with Archimedes about that. >> >> Graham. >> >> >> > > > > [Non-text portions of this message have been removed] > > > > ------------------------------------ > > Yahoo! Groups Links > > > -- Question with boldness even the existence of a God; because, if there be one, he must more approve of the homage of reason, than that of blind-folded fear. Thomas Jefferson ------------------------------------------------- Dennis Clark TTT Enterprises www.techtoystoday.com -------------------------------------------------
2009-05-15 by David VanHorn
On Thu, May 14, 2009 at 11:37 PM, dlc <dlc@frii.com> wrote: > Ahem, > > Water density is a constant, water _pressure_ increases with depth, > and if the ball acts the way my BC does, the air in the plastic ball > loses buoyancy as the water depth increases. But since my BC compresses > with depth and the plastic ball probably wouldn't, that might not be so. > These are basics every diver learns. So the effect is smaller, and the slope runs the other way, but it still works. :) Submarines compress, I imagine a plastic ball will too. -- There is no computer problem which cannot be solved by proper application of a sufficiently large hammer.
2009-05-15 by Graham Davies
--- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@...> wrote: > > From what I know, as the water > level rises the pressure at the > bottom increases causing more > of an uplift of an object held > at the bottom. OK, forget Archimedes, have a word with your tenth-grade physics teacher. Bouyancy has nothing to do with pressure. The upward force on an object imersed in a liquid is the weight of the liquid displaced minus the object's weight. To a first approximation, this is constant with depth of imersion, which is why your idea is a bad one. Arguing about second order effects is fine, but it's still a bad idea to use second order effects to make a measurement when sensors are available for the first order effect itself (pressure). As others have posted, there will be a very small variation of the force of bouyancy depending on the relative compressibility of the liquid and the object. Graham.
2009-05-15 by Brian
I was on Submarines in the Navy. They do compress but that is under a couple hundred feet of water. the compression of the plastic ball, could even be solid, should be small and still produce a measurable upforce with depth. Brian --- In AVR-Chat@yahoogroups.com, David VanHorn <microbrix@...> wrote:
> > On Thu, May 14, 2009 at 11:37 PM, dlc <dlc@...> wrote: > > Ahem, > > > > Water density is a constant, water _pressure_ increases with depth, > > and if the ball acts the way my BC does, the air in the plastic ball > > loses buoyancy as the water depth increases. But since my BC compresses > > with depth and the plastic ball probably wouldn't, that might not be so. > > These are basics every diver learns. > > So the effect is smaller, and the slope runs the other way, but it still works. > :) > > Submarines compress, I imagine a plastic ball will too. > > > -- > There is no computer problem which cannot be solved by proper > application of a sufficiently large hammer. >
2009-05-15 by Jim Wagner
This is exactly why the floaters in a Galilleo's Thermoscope hover at a specific depth. There is a density gradient in a column of fluid. At a greater depth, the floater is lighter than the fluid it displaces and at a lesser depth, it is heaver than the fluid it displaces. Definitely a second order effect, but still important. Jim Wagner On May 15, 2009, at 4:58 AM, Brian wrote: > > > I was on Submarines in the Navy. They do compress but that is under > a couple hundred feet of water. the compression of the plastic ball, > could even be solid, should be small and still produce a measurable > upforce with depth. > > Brian > --- In AVR-Chat@yahoogroups.com, David VanHorn <microbrix@...> wrote: > > > > On Thu, May 14, 2009 at 11:37 PM, dlc <dlc@...> wrote: > > > Ahem, > > > > > > Water density is a constant, water _pressure_ increases with > depth, > > > and if the ball acts the way my BC does, the air in the plastic > ball > > > loses buoyancy as the water depth increases. But since my BC > compresses > > > with depth and the plastic ball probably wouldn't, that might > not be so. > > > These are basics every diver learns. > > > > So the effect is smaller, and the slope runs the other way, but it > still works. > > :) > > > > Submarines compress, I imagine a plastic ball will too. > > > > > > -- > > There is no computer problem which cannot be solved by proper > > application of a sufficiently large hammer. > > > > > [Non-text portions of this message have been removed]
2009-05-15 by Robert Tilden
The liquid in the modern version of Galileo's Thermoscope may not be water... As I understand it, in the original version the floats were open, inverted 'cups' in which the trapped air changed volume with temperature, causing the floats to rise or fall. The modern version uses sealed floats and a supporting fluid that changes density with temperature. Besides, the question is how to measure the depth of a water tank, not its temperature. The incompressibility of water makes density changes with depth extremely small. The same doesn't hold true for its coefficient of thermal expansion. ----------------------------------- Bob Tilden, tilden@northwestern.edu High Energy Physics Group Northwestern University
-----Original Message----- From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf Of Jim Wagner Sent: Friday, May 15, 2009 9:59 AM To: AVR-Chat@yahoogroups.com Subject: Re: [AVR-Chat] Re: water level meter This is exactly why the floaters in a Galilleo's Thermoscope hover at a specific depth. There is a density gradient in a column of fluid. At a greater depth, the floater is lighter than the fluid it displaces and at a lesser depth, it is heaver than the fluid it displaces. Definitely a second order effect, but still important. Jim Wagner On May 15, 2009, at 4:58 AM, Brian wrote: > > > I was on Submarines in the Navy. They do compress but that is under > a couple hundred feet of water. the compression of the plastic ball, > could even be solid, should be small and still produce a measurable > upforce with depth. > > Brian > --- In AVR-Chat@yahoogroups.com, David VanHorn <microbrix@...> wrote: > > > > On Thu, May 14, 2009 at 11:37 PM, dlc <dlc@...> wrote: > > > Ahem, > > > > > > Water density is a constant, water _pressure_ increases with > depth, > > > and if the ball acts the way my BC does, the air in the plastic > ball > > > loses buoyancy as the water depth increases. But since my BC > compresses > > > with depth and the plastic ball probably wouldn't, that might > not be so. > > > These are basics every diver learns. > > > > So the effect is smaller, and the slope runs the other way, but it > still works. > > :) > > > > Submarines compress, I imagine a plastic ball will too. > > > > > > -- > > There is no computer problem which cannot be solved by proper > > application of a sufficiently large hammer. > > > > > [Non-text portions of this message have been removed] ------------------------------------ Yahoo! Groups Links
2009-05-15 by Ken Holt
No, the buoyancy of a submerged object does not increase with depth because water density does not increase with depth(not much anyway). The buoyancy is proportional to the differential pressure across the object. Jim Wagner wrote:
> > > But water density increases with depth, and thus apparent buoyancy > increases as the water gets deeper. > > Jim Wagner > Oregon Research Electronics > > On May 14, 2009, at 5:28 PM, Graham Davies wrote: > > > > > > > --- In AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com>, > "Brian" <blue_eagle74@...> wrote: > > > > > > ... a pressure sensor at the top > > > of the tank and a rod extending > > > down into the tank with a plastic > > > ball fixed at the end. the higher > > > the water level the more force on > > > the sensor. > > > > Are you suggesting that the force of buoyancy on the plastic ball > > will increase as the water level increases? You might want to have a > > word with Archimedes about that. > > > > Graham. > > > > > > > > [Non-text portions of this message have been removed] > >
2009-05-15 by Brian
I might be wrong but what you are saying is if I have a non-compressable ball weighing 10 oz displacing 1 cubic foot of water it would take the same amount of force to hold it under 50 foot of water as it would at 100 feet? If weight and volume didnt change what would keep it from going deeper? I think I might be missing something. Brian --- In AVR-Chat@yahoogroups.com, "Graham Davies" <Yahoo37849@...> wrote:
> > --- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@> wrote: > > > > From what I know, as the water > > level rises the pressure at the > > bottom increases causing more > > of an uplift of an object held > > at the bottom. > > OK, forget Archimedes, have a word with your tenth-grade physics teacher. > > Bouyancy has nothing to do with pressure. The upward force on an object imersed in a liquid is the weight of the liquid displaced minus the object's weight. To a first approximation, this is constant with depth of imersion, which is why your idea is a bad one. > > Arguing about second order effects is fine, but it's still a bad idea to use second order effects to make a measurement when sensors are available for the first order effect itself (pressure). As others have posted, there will be a very small variation of the force of bouyancy depending on the relative compressibility of the liquid and the object. > > Graham. >
2009-05-15 by Bob Paddock
> i want make project for measuring the level of water on the tank that > approximately 15 m high. what senssor that i should use ? http://www.analog.com/library/analogDialogue/archives/43-02/level_sensing.html The comments from that post point to real hardware: https://www.blogger.com/comment.g?blogID=11191427&postID=4471646240559987449&pli=1 -- http://www.wearablesmartsensors.com/ http://www.softwaresafety.net/ http://www.designer-iii.com/ http://www.unusualresearch.com/
2009-05-15 by Brian
I think I understand what you are saying. I know pressure is equal on all sides. So as the ball desends in the water the point of Bouyancy would raise from the center of the ball. Would this cause it to rise faster at deaper depths? Brian --- In AVR-Chat@yahoogroups.com, Phil Birkelbach <phil@...> wrote:
> > That is correct. A cubic foot of water weighs considerably more than > 10 oz. You could take that thing to the bottom of the Gulf and let it > go and it'll shoot straight back up. This does assume that it doesn't > get crushed somewhere along the way. Pressure does not matter. The > assumption that pressure is only acting on the bottom is a bad one. > The pressure pushes up, down sideways and every direction all at > once. The only pressure difference is the difference in the head > pressure of the water from the top of the object to the bottom of the > object and this is actually what causes it to be buoyant in the first > place. This pressure difference is constant at all depths (Assuming > the density change of the water is negligible. Which is a good > assumption at 15m but probably not at the bottom of the Gulf). The > force pushing up on the object is the difference between the objects > weight and the weight of the fluid it displaces. This is true of any > object in any fluid, including air. Yes you are being lifted up by > the atmosphere, but you're just too darn heavy to notice. > > Phil >
2009-05-16 by Phil Birkelbach
That is correct. A cubic foot of water weighs considerably more than 10 oz. You could take that thing to the bottom of the Gulf and let it go and it'll shoot straight back up. This does assume that it doesn't get crushed somewhere along the way. Pressure does not matter. The assumption that pressure is only acting on the bottom is a bad one. The pressure pushes up, down sideways and every direction all at once. The only pressure difference is the difference in the head pressure of the water from the top of the object to the bottom of the object and this is actually what causes it to be buoyant in the first place. This pressure difference is constant at all depths (Assuming the density change of the water is negligible. Which is a good assumption at 15m but probably not at the bottom of the Gulf). The force pushing up on the object is the difference between the objects weight and the weight of the fluid it displaces. This is true of any object in any fluid, including air. Yes you are being lifted up by the atmosphere, but you're just too darn heavy to notice. Phil
On May 15, 2009, at 8:10 PM, Brian wrote: > I might be wrong but what you are saying is if I have a non- > compressable ball weighing 10 oz displacing 1 cubic foot of water it > would take the same amount of force to hold it under 50 foot of > water as it would at 100 feet? If weight and volume didnt change > what would keep it from going deeper? I think I might be missing > something. > > Brian > > --- In AVR-Chat@yahoogroups.com, "Graham Davies" <Yahoo37849@...> > wrote: >> >> --- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@> wrote: >>> >>> From what I know, as the water >>> level rises the pressure at the >>> bottom increases causing more >>> of an uplift of an object held >>> at the bottom. >> >> OK, forget Archimedes, have a word with your tenth-grade physics >> teacher. >> >> Bouyancy has nothing to do with pressure. The upward force on an >> object imersed in a liquid is the weight of the liquid displaced >> minus the object's weight. To a first approximation, this is >> constant with depth of imersion, which is why your idea is a bad one. >> >> Arguing about second order effects is fine, but it's still a bad >> idea to use second order effects to make a measurement when sensors >> are available for the first order effect itself (pressure). As >> others have posted, there will be a very small variation of the >> force of bouyancy depending on the relative compressibility of the >> liquid and the object. >> >> Graham. >> > > > > > ------------------------------------ > > Yahoo! Groups Links > > >
2009-05-16 by dlc
Brian wrote: > I think I understand what you are saying. I know pressure is equal on all sides. So as the ball desends in the water the point of Bouyancy would raise from the center of the ball. Would this cause it to rise faster at deaper depths? If it were a balloon it'd be the opposite. The buoyancy of an object is the weight of the fluid that the object displaces. If you had a balloon it would shrink in volume as it was pulled further under water, with its reduction is volume so too comes a reduction in its buoyancy (as per Archimedes). This means that it would actually displace more (and become more buoyant) as it rose from the depths. Water does not compress so it will be a constant weight at every depth. Our ping pong ball won't compress much in only 15m of fluid so we can pretty much assume that its buoyancy will remain a constant at every depth. This leads us to an interesting depth gauge. If you had a device that was designed to compress (and not be crushed at the maximum depth) you could put that at the bottom of the tank and measure the compression. That compression would be directly correlated to the amount of fluid in the tank. No bouncing of radio or sound waves, no moving parts (or not moving very much anyway). DLC > Brian > > --- In AVR-Chat@yahoogroups.com, Phil Birkelbach <phil@...> wrote: >> That is correct. A cubic foot of water weighs considerably more than >> 10 oz. You could take that thing to the bottom of the Gulf and let it >> go and it'll shoot straight back up. This does assume that it doesn't >> get crushed somewhere along the way. Pressure does not matter. The >> assumption that pressure is only acting on the bottom is a bad one. >> The pressure pushes up, down sideways and every direction all at >> once. The only pressure difference is the difference in the head >> pressure of the water from the top of the object to the bottom of the >> object and this is actually what causes it to be buoyant in the first >> place. This pressure difference is constant at all depths (Assuming >> the density change of the water is negligible. Which is a good >> assumption at 15m but probably not at the bottom of the Gulf). The >> force pushing up on the object is the difference between the objects >> weight and the weight of the fluid it displaces. This is true of any >> object in any fluid, including air. Yes you are being lifted up by >> the atmosphere, but you're just too darn heavy to notice. >> >> Phil >> > > > > > ------------------------------------ > > Yahoo! Groups Links > > > -- Question with boldness even the existence of a God; because, if there be one, he must more approve of the homage of reason, than that of blind-folded fear. Thomas Jefferson ------------------------------------------------- Dennis Clark TTT Enterprises www.techtoystoday.com -------------------------------------------------
2009-05-16 by Graham Davies
--- In AVR-Chat@yahoogroups.com, "Brian" <blue_eagle74@...> wrote: > > I know pressure is equal on all sides. Hmm. This depends what you mean by "sides". If you're counting the top and the bottom, then no. Imaging a cube instead of the ball and imagine that it is oriented with one face parallel to the water surface. Label the sides P, Q, R and S, going around, and the top and bottom T and B. By symmetry, the pressure on P balances the pressure on R and Q balances S, so the cube does not move sideways. Or, strictly, I should say the forces balance, but the force equals the pressure times the area and the area of all faces of a cube is the same. How about the pressure on T and B? Well, the bottom is deeper in the water than the top, so the pressure on B will be greater than the pressure on T. The cube is being pushed up from the bottom with a greater force than it is being pushed down from the top. That, in a nutshell, is bouyancy. With a cube, it's almost trivial to caculate the net force, but Archimedes showed that the same rule applies to all objects, whatever their shape. The force of bouyancy is equal to the weight of fluid displaced. > So as the ball desends in the water > the point of Bouyancy would raise > from the center of the ball. I'm not sure what you mean by "the point of Bouyancy". > Would this cause it to rise faster > at deaper depths? If the ball and the water are considered incompressible, no. As I hope we've shown, the force of bouyancy is constant with depth, so the force tending to make the ball rise is constant. If the viscosity of the fluid is also constant, for example the temperature is constant, then the ball will rise at constant speed. If the ball is compressible, perhaps a basketball, then as it rises and the pressure decreases it will expand. As it expands it will displace more water and the force of bouyancy will increase. So, it will rise slower at greater depth than near the surface. If the ball is not compressible and the fluid is, perhaps airated water, then at greater depth the constant volume of the ball displaces a greater weight of the fluid and it will rise faster. It would be possible to reach a point of stable equilibrium in which the force of bouyancy is exactly equal to the weight of the ball and it remains at some constant depth. If it rises, the fluid density decreases and bouyancy is lost so it sinks again. If it sinks too far, the fluid density increases and the additional bouyancy causes it to rise. Graham.