If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?

Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?

you can.


If the material is conductive.


You can also measure the capacitance if its an insulator


But modern oil gauges and height gauges prefer to use ultrasonic
rangefinding on the top of the liquid.


Not always a good idea to have electrical conductors in flammable liquids..

On Jan 6, 5:25*pm, The Natural Philosopher
wrote:
Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?

you can.

If the material is conductive.

You can also measure the capacitance if its an insulator

But modern oil gauges and height gauges prefer to use ultrasonic
rangefinding on the top of the liquid.

Not always a good idea to have electrical conductors in flammable liquids...

The traditional automotive petrol guage sender is immersed in petrol/
petrol vapour. No danger if there is no air.


Much traditional instrumentation in boilerhouses depends on electrodes
immersed in water or sometimes mercury eg for determining draught in
chimneys and CO2 levels in combustion gases via the resistance of the
water.

Fluids don't have capacitance. They might have permittivity.
http://en.wikipedia.org/wiki/Relativ...c_permittivity

On Jan 6, 5:18*pm, Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?


Basically too many variables. You would have to know the diameter &
lenght of the container, the diameter of the wires, the depth of
their immersion and the resistivity of the liquid.
Even then you could only determine any difference in the levels of
liquid. not the absolute amount unless the wires touched the bottom of
the container and assuming it was an insulator.

harry wrote:
On Jan 6, 5:25 pm, The Natural Philosopher
wrote:
Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?
you can.

If the material is conductive.

You can also measure the capacitance if its an insulator

But modern oil gauges and height gauges prefer to use ultrasonic
rangefinding on the top of the liquid.

Not always a good idea to have electrical conductors in flammable liquids..

The traditional automotive petrol guage sender is immersed in petrol/
petrol vapour. No danger if there is no air.


Much traditional instrumentation in boilerhouses depends on electrodes
immersed in water or sometimes mercury eg for determining draught in
chimneys and CO2 levels in combustion gases via the resistance of the
water.

Fluids don't have capacitance.

two wires dipped in them, do, however.


They might have permittivity.
http://en.wikipedia.org/wiki/Relativ...c_permittivity

On 06/01/2012 17:18, Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?

Only works if the resistance is in the right range. If the water is
impure then it conducts too well and looks like a dead short. Tiny
changes in the (im)purity of the water would affect the "level". That is
dipping your hand in for instance providing more ionic salts.

There is a trick using a central wire and an outer metal tube as a
variable capacitor with the central wire insulated that exploits the
difference in relative permitivity between the liquid and air. Sort of
an electronic version of the old manometer type oil tank measure.

These days most systems use an ultrasonic rangefinder to determine
distance to liquid surface. They seem to last ages (unless the guy who
delivers fuel sometimes replaces the battery unknown to me).

Regards,
Martin Brown

On Fri, 6 Jan 2012 09:48:03 -0800 (PST), harry wrote:

On Jan 6, 5:25Â*pm, The Natural Philosopher
wrote:
Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?

you can.

If the material is conductive.

You can also measure the capacitance if its an insulator

But modern oil gauges and height gauges prefer to use ultrasonic
rangefinding on the top of the liquid.

Not always a good idea to have electrical conductors in flammable liquids..

The traditional automotive petrol guage sender is immersed in petrol/
petrol vapour. No danger if there is no air.


Much traditional instrumentation in boilerhouses depends on electrodes
immersed in water or sometimes mercury eg for determining draught in
chimneys and CO2 levels in combustion gases via the resistance of the
water.

Fluids don't have capacitance. They might have permittivity.
http://en.wikipedia.org/wiki/Relativ...c_permittivity

permitivity results in capacitance .. the amount depends on the distance
between conductors and their area ... oh and the permitivity of the
dielectric
--
(º€¢.¸(¨*€¢.¸ ¸.€¢*¨)¸.€¢Âº)
.€¢Â°€¢. Nik .€¢Â°€¢.
(¸.€¢Âº(¸.€¢Â¨* *¨€¢.¸)º€¢.¸)

On 7/01/2012 6:56 a.m., harry wrote:
On Jan 6, 5:18 pm, wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?


Basically too many variables. You would have to know the diameter&
lenght of the container, the diameter of the wires, the depth of
their immersion and the resistivity of the liquid.
Even then you could only determine any difference in the levels of
liquid. not the absolute amount unless the wires touched the bottom of
the container and assuming it was an insulator.

All able to be calibrated.

In message
,
harry writes
On Jan 6, 5:25*pm, The Natural Philosopher
wrote:
Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?

you can.

If the material is conductive.

You can also measure the capacitance if its an insulator

But modern oil gauges and height gauges prefer to use ultrasonic
rangefinding on the top of the liquid.

Not always a good idea to have electrical conductors in flammable liquids..

The traditional automotive petrol guage sender is immersed in petrol/
petrol vapour. No danger if there is no air.


Much traditional instrumentation in boilerhouses depends on electrodes
immersed in water or sometimes mercury eg for determining draught in
chimneys and CO2 levels in combustion gases via the resistance of the
water.

Fluids don't have capacitance.


Duh - The wires have a capacitance between them and the fluid (assuming
its an insulator) acts as a dielectric between the wires





--
geoff

In message
,
harry writes
On Jan 6, 5:18*pm, Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?


Basically too many variables.

Not once its calibrated

--
geoff

geoff wrote:
In message
,
harry writes
On Jan 6, 5:18 pm, Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?


Basically too many variables.

Not once its calibrated

until you change the fluid composition...

In message , The Natural Philosopher
writes
geoff wrote:
In message
,
harry writes
On Jan 6, 5:18 pm, Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?


Basically too many variables.
Not once its calibrated

until you change the fluid composition...


Well yes, I was assuming a certain level of common sense in my reply

--
geoff

On 06/01/2012 17:25, The Natural Philosopher wrote:
Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?

you can.


If the material is conductive.


You can also measure the capacitance if its an insulator


But modern oil gauges and height gauges prefer to use ultrasonic
rangefinding on the top of the liquid.


Not always a good idea to have electrical conductors in flammable liquids..

That's when you use intrinsically safe devices and either zener barriers
or galvanic isolators - restricting the voltage (typically 28V dc max)
and current (typically 20-odd milliamps) so that there is not enough
energy supplied or stored to ignite any vapours.

SteveW

On Jan 6, 9:46*pm, geoff wrote:
In message
,
harry writes





On Jan 6, 5:25*pm, The Natural Philosopher
wrote:
Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?

you can.

If the material is conductive.

You can also measure the capacitance if its an insulator

But modern oil gauges and height gauges prefer to use ultrasonic
rangefinding on the top of the liquid.

Not always a good idea to have electrical conductors in flammable liquids..

The traditional automotive petrol guage sender is immersed in petrol/
petrol vapour. No danger if there is no air.

Much traditional instrumentation in boilerhouses depends on electrodes
immersed in water or sometimes mercury eg for determining *draught in
chimneys and CO2 levels in combustion gases via the resistance of the
water.

Fluids don't have capacitance.

Duh - The wires have a capacitance between them and the fluid (assuming
its an insulator) acts as a dielectric between the wires

--
geoff- Hide quoted text -

- Show quoted text -

I thought the OP was about measuring liquid?
Which is not a capacitor.

harry wrote:
On Jan 6, 9:46 pm, geoff wrote:
In message
,
harry writes





On Jan 6, 5:25 pm, The Natural Philosopher
wrote:
Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?
you can.
If the material is conductive.
You can also measure the capacitance if its an insulator
But modern oil gauges and height gauges prefer to use ultrasonic
rangefinding on the top of the liquid.
Not always a good idea to have electrical conductors in flammable liquids..
The traditional automotive petrol guage sender is immersed in petrol/
petrol vapour. No danger if there is no air.
Much traditional instrumentation in boilerhouses depends on electrodes
immersed in water or sometimes mercury eg for determining draught in
chimneys and CO2 levels in combustion gases via the resistance of the
water.
Fluids don't have capacitance.
Duh - The wires have a capacitance between them and the fluid (assuming
its an insulator) acts as a dielectric between the wires

--
geoff- Hide quoted text -

- Show quoted text -

I thought the OP was about measuring liquid?
Which is not a capacitor.

Put two plates in a liquid. You now have a capacitor whose value depends
on the size of the plates, their distance apart and the permittivity
(A.K.A. dielectric constant) of the liquid. It doesn't matter greatly if
the insulation is the liquid or a thin insulating coating on the plates,
though you can get better repeatability with an insulating coating.

If you keep the distance apart and the permittivity constant, then you
can measure the level by measuring the capacitance between the plates,
as long as the level stays between the top and bottom of the plates.

--
Tciao for Now!

John.

In message
,
harry writes

Fluids don't have capacitance.

Duh - The wires have a capacitance between them and the fluid (assuming
its an insulator) acts as a dielectric between the wires

--
geoff- Hide quoted text -

- Show quoted text -

I thought the OP was about measuring liquid?
Which is not a capacitor.

Any two conductors with an insulator in between form a capacitor

You are obviously out of your depth here - stop digging

--
geoff

geoff wrote:
In message , The Natural Philosopher
writes
geoff wrote:
In message
,
harry writes
On Jan 6, 5:18 pm, Neil wrote:
If you have a container and you put two vertical parallel wires in it,
why can't you determine the quantiy of a liquid poured into that
container based on the resistance measured between the two wires?


Basically too many variables.
Not once its calibrated

until you change the fluid composition...


Well yes, I was assuming a certain level of common sense in my reply

Always a dangerous thing with the likes of Dribble, Dennis and harry about.

Which is why this particular sort of transducer is NOT actually widely used.

Floats on arms and ultrasonics are just more reliable over a range of
fluids.

On Sat, 07 Jan 2012 01:04:13 +0000, Steve Walker
wrote:

Not always a good idea to have electrical conductors in flammable liquids..

That's when you use intrinsically safe devices and either zener barriers
or galvanic isolators - restricting the voltage (typically 28V dc max)
and current (typically 20-odd milliamps) so that there is not enough
energy supplied or stored to ignite any vapours.

I'd understood the vapour concentration in a typical petrol tank was
too high for explosion risk. Otoh, it's not entirely unknown for one
to go up.
Years ago I saw a pic of static discharges in an Avgas tank - slightly
worrying.

On Jan 8, 12:26*am, wrote:
On Sat, 07 Jan 2012 01:04:13 +0000, Steve Walker

wrote:
Not always a good idea to have electrical conductors in flammable liquids..

That's when you use intrinsically safe devices and either zener barriers
or galvanic isolators - restricting the voltage (typically 28V dc max)
and current (typically 20-odd milliamps) so that there is not enough
energy supplied or stored to ignite any vapours.

I'd understood the vapour concentration in a typical petrol tank was
too high for explosion risk. Otoh, it's not entirely unknown for one
to go up.
Years ago I saw a pic of static discharges in an Avgas tank - slightly
worrying.

When refueling aircraft, you are supposed to connect an earth lead to
them before you start. Especially important if they have just landed.
The rubber dispensing hose is a special antistatic job too that has to
be tested regularly. It is of a resistance to discharge any static
electricity but not so low a resistance to cause a spark.
Fuel vapour is displaced out of the tank as the fuel goes in.

harry wrote:

On Jan 8, 12:26 am, wrote:
On Sat, 07 Jan 2012 01:04:13 +0000, Steve Walker

wrote:
Not always a good idea to have electrical conductors in flammable
liquids..

That's when you use intrinsically safe devices and either zener barriers
or galvanic isolators - restricting the voltage (typically 28V dc max)
and current (typically 20-odd milliamps) so that there is not enough
energy supplied or stored to ignite any vapours.

I'd understood the vapour concentration in a typical petrol tank was
too high for explosion risk. Otoh, it's not entirely unknown for one
to go up.
Years ago I saw a pic of static discharges in an Avgas tank - slightly
worrying.

When refueling aircraft, you are supposed to connect an earth lead to
them before you start. Especially important if they have just landed.
The rubber dispensing hose is a special antistatic job too that has to
be tested regularly. It is of a resistance to discharge any static
electricity but not so low a resistance to cause a spark.
Fuel vapour is displaced out of the tank as the fuel goes in.

Surprised they don't have a vapour recovery system...

--
Tim Watts

On Sun, 8 Jan 2012 01:30:31 -0800 (PST), harry
wrote:

When refueling aircraft, you are supposed to connect an earth lead to
them before you start. Especially important if they have just landed.
The rubber dispensing hose is a special antistatic job too that has to
be tested regularly. It is of a resistance to discharge any static
electricity but not so low a resistance to cause a spark.
Fuel vapour is displaced out of the tank as the fuel goes in.

I know.
These were pics taken of the inside of a fuel tank *as it was being
refuelled*, with anti-static precautions in place. It was remarkable
how the whole lot didn't go up.
I presume it was nothing unusual, but still...

On Jan 8, 9:36*am, Tim Watts wrote:
harry wrote:
On Jan 8, 12:26 am, wrote:
On Sat, 07 Jan 2012 01:04:13 +0000, Steve Walker

wrote:
Not always a good idea to have electrical conductors in flammable
liquids..

That's when you use intrinsically safe devices and either zener barriers
or galvanic isolators - restricting the voltage (typically 28V dc max)
and current (typically 20-odd milliamps) so that there is not enough
energy supplied or stored to ignite any vapours.

I'd understood the vapour concentration in a typical petrol tank was
too high for explosion risk. Otoh, it's not entirely unknown for one
to go up.
Years ago I saw a pic of static discharges in an Avgas tank - slightly
worrying.

When refueling aircraft, you are supposed to connect an earth lead to
them before you start. Especially important if they have just landed.
The rubber dispensing hose is a special antistatic job too that has to
be tested regularly. *It is of a resistance to discharge any static
electricity but not so low a resistance to cause a spark.
Fuel vapour is displaced out of the tank as the fuel goes in.

Surprised they don't have a vapour recovery system...

What do you do with it after you have recovered it?

harry wrote:

On Jan 8, 9:36 am, Tim Watts wrote:
harry wrote:
On Jan 8, 12:26 am, wrote:
On Sat, 07 Jan 2012 01:04:13 +0000, Steve Walker

wrote:
Not always a good idea to have electrical conductors in flammable
liquids..

That's when you use intrinsically safe devices and either zener
barriers or galvanic isolators - restricting the voltage (typically
28V dc max) and current (typically 20-odd milliamps) so that there is
not enough energy supplied or stored to ignite any vapours.

I'd understood the vapour concentration in a typical petrol tank was
too high for explosion risk. Otoh, it's not entirely unknown for one
to go up.
Years ago I saw a pic of static discharges in an Avgas tank - slightly
worrying.

When refueling aircraft, you are supposed to connect an earth lead to
them before you start. Especially important if they have just landed.
The rubber dispensing hose is a special antistatic job too that has to
be tested regularly. It is of a resistance to discharge any static
electricity but not so low a resistance to cause a spark.
Fuel vapour is displaced out of the tank as the fuel goes in.

Surprised they don't have a vapour recovery system...

What do you do with it after you have recovered it?

Same as the petrol station do when they recover it (which is rare in this
country).

http://en.wikipedia.org/wiki/Vapor_recovery

Presumably put it back in the storage tank?
--
Tim Watts