Smallest liquid sensor design ?

M

Marcel Gonzalez

Guest
Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?

Thanks.
Marcel
 
On 26 May 2004 06:23:17 -0700, dragonbreed@aol.com (Marcel Gonzalez)
wrote:

Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?
Click to expand...
---
Use a self-heated thermistor. When not in contact with the liquid the
heat capacity of its environment will be lower than when it's in
contact with the liquid, giving you a sharply delineated region
between contact and non-contact (presence and absence) of the fluid.

--
John Fields
 
On 26 May 2004 06:23:17 -0700, the renowned dragonbreed@aol.com
(Marcel Gonzalez) wrote:

Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?
Click to expand...
If you can use conductivity, make a sensor from mineral-insulated
cable with a hermetic termination and electrodes at the wet end.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In article <c12f8b92.0405260523.77accfba@posting.google.com>,
Marcel Gonzalez <dragonbreed@aol.com> wrote:
Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?
Click to expand...
Depending on how clear the liquid is, you can use a fiber-optic detector.
Normally the light goes down one fiber and is total internal reflected
into the other. The liquids index is greater than air's so when the
liquid hits the air side of the reflecting surface, the total internal
reflection stops because the index change is too small for the angle.

--
--
kensmith@rahul.net forging knowledge
 
On a sunny day (26 May 2004 06:23:17 -0700) it happened dragonbreed@aol.com
(Marcel Gonzalez) wrote in <c12f8b92.0405260523.77accfba@posting.google.com>:

Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?

Thanks.
Marcel
2 electrodes.
Click to expand...
Or if the thing is metal, only one.
Fluid need to be a bit conductive.
Electrode via 1 M to + 5.
Voltage will drop if in fluid.
JP
 
Small thermister (glass type) size of a matchead. You can drive it from an
opamp or a microcontroller.
 
"John Fields" <jfields@austininstruments.com> wrote in message
news:n689b0p39msfgnbtljkc3bjs07u9j7o1d9@4ax.com...
On 26 May 2004 06:23:17 -0700, dragonbreed@aol.com (Marcel Gonzalez)
wrote:

Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?

---
Use a self-heated thermistor. When not in contact with the liquid the
heat capacity of its environment will be lower than when it's in
contact with the liquid,
Click to expand...
Is that always true for all combinations of liquid and gas (plus vapor from
the liquid, of course).
 
On Wed, 26 May 2004 12:01:45 -0700, "Richard Henry" <rphenry@home.com>
wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:n689b0p39msfgnbtljkc3bjs07u9j7o1d9@4ax.com...
On 26 May 2004 06:23:17 -0700, dragonbreed@aol.com (Marcel Gonzalez)
wrote:

Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?

---
Use a self-heated thermistor. When not in contact with the liquid the
heat capacity of its environment will be lower than when it's in
contact with the liquid,

Is that always true for all combinations of liquid and gas (plus vapor from
the liquid, of course).
Click to expand...
---
If you doubt it, why don't _you_ do the legwork needed to prove that
it isn't true and then post your incontrovertible evidence?

--
John Fields
 
In sci.electronics.design Richard Henry <rphenry@home.com> wrote:
"John Fields" <jfields@austininstruments.com> wrote in message
news:n689b0p39msfgnbtljkc3bjs07u9j7o1d9@4ax.com...
On 26 May 2004 06:23:17 -0700, dragonbreed@aol.com (Marcel Gonzalez)
wrote:

Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?

---
Use a self-heated thermistor. When not in contact with the liquid the
heat capacity of its environment will be lower than when it's in
contact with the liquid,

Is that always true for all combinations of liquid and gas (plus vapor from
the liquid, of course).
Click to expand...
Pretty much, unless you'r near the triple-point of the liquid in question.
 
There are reflective sensors with integrated photodiode / LED inside. I
thingk the way they work is that when immersed in liquid the light "escapes"
the housing, when out of the liquid total internal reflection occurs and
thelight is sensed by the internal detector. From memory the sensing bit was
about the same size as a 5mm LED - the ones I saw had a ferrule assembly for
bulkhead/thread mounting. Try RS or Farnell if they sound useful. I think
the specs mentioned refractive index of the fluid - I know they work for
petrol.

rob


"Marcel Gonzalez" <dragonbreed@aol.com> wrote in message
news:c12f8b92.0405260523.77accfba@posting.google.com...
Hello. I would like to sense the presense of a clear non-flammable
liquid in a 5/16" x 30" tubular reservoir. I have no choice but to
insert the sensor from the top of the tube in my application (not by
the side). Does anyone know a small enough sensor or sensor design
that will fit inside this tube (5/16" inner dimension)?

Thanks.
Marcel
Click to expand...
 
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