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'[EE]: Electronic Level Sensor'
2002\07\09@082124 by Terence Gunderson

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Greetings and thanks in advance for any and all input:

I need to have a platform automatically level itself.  I am looking for a suitable sensor to electronically sense when the platform is at level.  The output of the sensor will be input to a micro the micro will then adjust jack screws until it sees a level condition.

Terry

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2002\07\09@092404 by chucksea

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Used these on railroad equipment in a past life.

http://www.schaevitz.com/products/inertial/index.html

These might be a little cheaper:
http://www.schaevitz.com/stock/quote.html#Tilt Sensors

chuckc




On Mon, 9 Sep 2002 07:18:51 -0500 Terence Gunderson <.....tgunderKILLspamspam@spam@GTE.NET> wrote:

Greetings and thanks in advance for any and all input:

I need to have a platform automatically level itself.  I am looking for a
suitable sensor to electronically sense when the platform is at level.  The
output of the sensor will be input to a micro the micro will then adjust jack
screws until it sees a level condition.

Terry

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2002\07\09@115057 by Bob Blick

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Hi Terry,

The highest accuracy is with electrolytic tilt sensors.

I have used sensors from two companies, Fredericks and Spectron. If you
need absolutely the best, Fredericks makes the best. You can achieve 2 or
3 arc-seconds over a commercial temperature range. Spectron's best is not
quite so good but considerably cheaper.

Fredericks also makes a cute little 2-axis sensor that is fairly
accurate, I think 30 arc-seconds or so, and it is also fairly linear so
you can use it to measure angle, not just a null.

If you are buying in small quantities, Fredericks might also be easier to
deal with.

Cheerful regards,

Bob

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2002\07\09@130441 by Robert Rolf

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Look at what the Recreational Vehicle industry uses for it's 'autolevel' jacks.
It can be as simple as set of 4 mercury switches (or one bubble switch with 5
leads [4 directions + common])

I'd recommend the Analog Devices ADXL202 two axis accelerometer with pulse
width modulated (duty cycle actually) outputs. Not cheap, but very linear and
easy to interface to a PIC.

Terence Gunderson wrote:
{Quote hidden}

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2002\07\09@152604 by Scott M. Thomas

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These are not terribly accurate, but they are inexpensive.  Can sense level
withing +-15 deg.

http://rocky.digikey.com/WebLib/Sharp/Web%20Data/gp1s36.pdf

{Original Message removed}

2002\07\10@044434 by Pang

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Hi Scott,

I think the datasheet does not state the sense level of +-15 degrees. Both
the transistor will be ON at +15 and -15 degrees. If the degree of tilting
continue to be increase, one of the transistor will have be in undefine
state. And that undefine state will continue until it reaches 75 degrees,
where it will be in the OFF state.

I didn't get what i been looking for   ...(a cheap tilt sensor), but at
least this is getting very near to the spec that i want. If only there is a
similar component with a slightly better angle characteristics. :-)

Best rgds,
pang


----- Original Message -----
From: "Scott M. Thomas" <KILLspamscottKILLspamspamDBT.NET>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Wednesday, July 10, 2002 3:24 AM
Subject: Re: [EE]: Electronic Level Sensor


> These are not terribly accurate, but they are inexpensive.  Can sense
level
> withing +-15 deg.
>
> http://rocky.digikey.com/WebLib/Sharp/Web%20Data/gp1s36.pdf
>
> {Original Message removed}

2002\07\10@115256 by Mike Pink
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Hi Pang

Just joined the list so may have picked up late on this.

Why not use 4 simple tilt switches (about #0.60/ $1 each ) and tilt each one
towards its respective corner so that when level all 4 are 'tilted'. Then as
the platform tips over the high side tilt switch will become level telling
you which direction to adjust. If you want to be really cheap you could use
plastic tubes with ball bearings and contact wires.

Hope this helps

Mike


----- Original Message -----
From: "Pang" <spamBeGoneklpangspamBeGonespamAICM.COM.MY>
To: <TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU>
Sent: Wednesday, July 10, 2002 4:33 AM
Subject: Re: [EE]: Electronic Level Sensor


{Quote hidden}

> > {Original Message removed}

2002\07\10@140250 by Pic Dude

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Another option...

I really like water levels, as they are "self-calibrating".
Perhaps you can use something based on that.  For example,
use a hose with a water-level sensor on both ends.  This
could be something ultrasonic, something optical on the
outside with colored water, or electrodes in the water, etc.
And you'd need 2 such arrangements to level a platform with
3 adjust points, or 3 arrangements if you have 4 adjustment
points.

Cheers,
-Neil.





{Original Message removed}

2002\07\10@184423 by Martin Farrell

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In message <EraseMEBJEDIBGCHKOMPGADEIGGEEBDCNAA.picdudespampilottools.com>, Pic
Dude <RemoveMEpicdudeEraseMEspamEraseMEPILOTTOOLS.COM> writes
>Another option...
>
>I really like water levels, as they are "self-calibrating".
>Perhaps you can use something based on that.  For example,
>use a hose with a water-level sensor on both ends.  This
>could be something ultrasonic, something optical on the
>outside with colored water, or electrodes in the water, etc.
>And you'd need 2 such arrangements to level a platform with
>3 adjust points, or 3 arrangements if you have 4 adjustment
>points.
>

A good way of making a non contact sensor for water is to make an
oscillator with a 74HC14 with 1M feedback and a self adhesive metal tape
round the pipe as the capacitor.(No 'physical' ground is required).
Count the frequency with a PIC. I've used a 12CE518 storing the smoothed
trip count (level) in EEPROM on whirlpool bath level monitors with no
problems.

--
Martin Farrell

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2002\07\10@213617 by Pang

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Hi Mike and Neil,

Frankly, I am not able to correctly visualise Mike suggestion. Are you
trying to say we can install a few tilt switches with different angles. For
example,

Sensor A install in such a way that it will be tilted if the platform is
raised by 15 deg.
Sensor B install  ........... 30 deg.
Sensor C .......... 45 deg.

So let say, a car (that's my intention :-)...) is tilted by 15 deg from
normal, then sensor A will be tilted while sensor B & C will not be
tilted.... OR if the tilted angle is 30 then A-off, B-on and C-off.

What if in-between 15 and 30 deg?  I don't know.....
I guess the GP1S36 will be quite useful if it doesn't have the undefined
state between 15 and 75 deg.

Have never use an ultrasonic or water level sensor before, so wondering how
high a resolution that can provide. Besides, if high resolution is needed
(+-5mm) then the reading could be affected by the water temperature, maybe
then we need another temp sensor....any other ideas?....

Best rgds,
pang

----- Original Message -----
From: "Pic Dude" <RemoveMEpicdudeTakeThisOuTspamspamPILOTTOOLS.COM>
To: <EraseMEPICLISTspamspamspamBeGoneMITVMA.MIT.EDU>
Sent: Thursday, July 11, 2002 1:58 AM
Subject: Re: [EE]: Electronic Level Sensor


{Quote hidden}

> {Original Message removed}

2002\07\10@214737 by Pic Dude

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This sounds neat, but I worry that if we're measuring
capacitance, then external influences may throw off the
calibration.  For example, when I first saw this post, I
related it to a problem I had building a corner scale for
a vehicle.  It is very necessary to keep the wheels level.
I wonder how the large chunk of metal in the area (the
car) will affect the sensor output.

Cheers,
-Neil.



{Original Message removed}

2002\07\10@220518 by Pic Dude

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Pang,

This is scary -- see my last post from a couple minutes ago,
where I was relating the platform leveling to a car scale,
which needs to be level.  Funny you should say that your's
is also for a car.

IMHO, 15 deg resolution will not be useful.  However, picture
this...  A non-electronic water level is a simple device that
tells you what perfect level is no matter what the temp, etc.
Get a clear hose, hold it in the shape of a "U" with both
ends open and fill it with water.  You'll notice that the
top of water column are always at the same height, no matter
what you do with the hose.  You can move the ends apart many
feet and it will still show you what is perfectly level.
Another trick is to drop some oil on the top of each column
to be able to read it easier.

All you need now is some way to electronically measure the
water level at both ends.  You can use an array of optical
sensors (I believe digikey has these in a single package of
16 or 32 sensors), and color the water.  Or some ultrasonic
sensor at the top of each end, both pointing downwards into
the water.  Perhaps you can put some type of light/hollow
metal ball on top of the water on each end, and use a hall-
effect sensor to detect it's level.  Etc, etc, etc.

Cheers,
-Neil.






{Original Message removed}

2002\07\11@035559 by Mike Pink

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Hi Pang

For example lets take 4 single axis tilt switches that switch 'off' when
tilted.
Place them on a pcb aligned north, south, east, & west, and tilt the
outermost edge of each of the 4 switches so that each just switches 'off'.
Now when the board is level all 4 switches are tilted and therefore 'off'.
Now if you lower the north side what happens. The north switch just becomes
more tilted and remains 'off', the east & west switches roll slightly but do
nothing, but the south becomes level and switches 'on'.
All that needs to be done is to use this 'on' signal to raise the north side
until south switch tilts and is 'off'.

So in its crudest form by connecting south's "tilt switch" to north's "raise
motor" and the same for north tilt / south motor and again for the east
/west the whole thing becomes automatic.

oh! and no pic. sorry I did say it was crude.

Looking at the original posting I see you mention "jack screw". Assuming the
installation is level in the first place why don't you just count the number
of turns {mag-read switch, hall effect switch, etc} of each screw and use a
pic to balance the number of turns. This would be easier and a lot more fail
safe.






----- Original Message -----
From: "Pang" <RemoveMEklpangKILLspamspamAICM.COM.MY>
To: <PICLISTSTOPspamspamspam_OUTMITVMA.MIT.EDU>
Sent: Wednesday, July 10, 2002 9:25 PM
Subject: Re: [EE]: Electronic Level Sensor


> Hi Mike and Neil,
>
> Frankly, I am not able to correctly visualise Mike suggestion. Are you
> trying to say we can install a few tilt switches with different angles.
For
{Quote hidden}

how
{Quote hidden}

> > {Original Message removed}

2002\07\11@100350 by Martin Farrell

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In message <EraseMEBJEDIBGCHKOMPGADEIGGMECMCNAA.picdudespamEraseMEpilottools.com>, Pic
Dude <@spam@picdude@spam@spamspam_OUTPILOTTOOLS.COM> writes
>This sounds neat, but I worry that if we're measuring capacitance, then
>external influences may throw off the calibration.  For example, when I
>first saw this post, I related it to a problem I had building a corner
>scale for a vehicle.  It is very necessary to keep the wheels level. I
>wonder how the large chunk of metal in the area (the car) will affect
>the sensor output.

It will but not as much as you'd think. The sensor capacitance to the
water is defined by its area, the thickness of the tube( say 1mm) and
its dielectric constant say 5. The sensor capacitance to the car has a
much larger distance (~100mm) and relative dielectric is only 1.
Ignoring (large) edge effects, the effective area of the sensor-car
capacitance is still defined by the sensor dimensions so we have 500:1
ratio in sensitivities at that range.

I can report that after extensive research, a beer filled 85Kg test
object sitting on the edge of the bath cutting it's toenails does not
upset the sensor by more than a few percent.
The main problem is that most of the capacitance is due to the film of
water on the inside of the tube. It should be coated to break the film
quickly.

A better technique, which I don't use for fear of electrocuting
customers (generally not a good USP), is a self heated NTC thermistor,
immersed in the water and measuring the voltage across it as the water
dissipates the self heating.

Regards Martin

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2002\07\11@103235 by Dave Mumert

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Hi Terry

Check out the products at
http://www.frederickscom.com

They have a number of tilt sensors and the electronics to drive them.  They
have single and dual axis units with repeatability of <.2 arc minutes.

Dave

{Original Message removed}

2002\07\15@134748 by David Minkler

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Hi,

How accurately?  Vibration?  One-up or commercial?  How fast does it
move when leveling?  One axis or two?  How much space (volume) do you
have to work with?  Do you have (unusual) cost constraints?

Regards,
Dave

Terence Gunderson wrote:
{Quote hidden}

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