Re: Measuring liquid level with bubbles using an ultrasonic transducer

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On 28 Feb 2007 15:54:05 -0800, overgeo@xxxxxxxxx wrote in message
<1172706845.461279.186970@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:

>Sorry for my late answer, i have been doing other projects. The liquid
>is oil and is viscous, the accuracy is not a lot, the height of the
>tank is 5 meter and an error of 10 cm is perfectly asumible.
>
>So i can use a differential pressure transducer, with one transducer
>that measures the pressure in the head of the tank and another one
>that measures the pressure in the bottom of the tank, and with the
>difference of both pressures i get the heigh of the liquid with this
>formule h = differential pressure/(specific gravity * g)  where g =
>acceleration due to gravity.
>
>I have been looking for some sensors, and in this page there are some
>of them. http://www.sensotec.com/pdf_catalog06/fp2000.pdf, the fp2000
>wet/wet differential, i think will be suitable, what do you think?
>
>To calculate the pressure range, i can use the formule.
>
>max differential pressure =    h_max * (specific gravity * g),  is
>this correct?
>
>In addition the idea of the pipe was good, but i think that it will be
>easier the differential pressure.
>Finally thanks so much for all your answers
>

I see that this is an industrial application, not home, so I recommend
industrial components and mounting of the transducer outside the tank. This
will better address the explosion hazard issues the specifics of which
depend on the fluid, application and location.

- Yes, that is the equation I provided, but see below for converting
transducer output voltage directly to meters of fluid.

- You said that the upper part of the tank would be under vacuum, thus the
differential transducer.  The 5m of fluid water requires ~=500 millibar ~=
50kP  =~7.25 PSI. The nearest higher value offered by Honeywell/Sensotec
seems to be the 10PSI   differential (~= 70kPa) But see below.

- My preference is for 0-10vdc output assuming the associated electronics
are nearby.

- So with 10 PSI range and 10vdc Full Scale Output (FSO) the output is
1 PSI/volt = 0.701 meters of water /volt

(You'll want to check my arithmetic! 14.7 PSI = 33.9 feet of water = 10.3
meters of water. )

For a fluid with specific gravity of n, the output would be (0.70/n)
meters/volt output. For example, for an oil with a sp. gr. of 0.8, the
output would be (0.70/0.8)= 0.875 meters oil/volt output.

- The wetted materials of the Sensotec/Honeywell transducers
(Hastelloy/lnconel C276 and 316SS) are suitable for any organic fluid.

- You want differential wet/wet as I specified previously.

- My preference would be for 1/4" NPT female fittings on the transducer
because this facilitates connection to 1/4"OD x 1/8" ID stainless steel
tubing using 1/4" SS-400-6  Swagelock fittings.

I'd make a stainless steel flange and mount two SS-400-1-4BT Swagelock
bored-through or SS-400-11-4  bulkhead stainless steel fittings on it and
run the tubing through the fittings into the tank. The tube that goes to
the bottom should be sealed (pinch it off) at the bottom and a slot cut in
it a known distance up. This is so that you can set the tube to a known
depth from the bottom (lower it as far as it will go)and still avoid having
the input clogged with whatever debris may be on the bottom of the tank.

Then connect the transducer _outside_ the tank at or below the level of the
intake on the bottom with additional 1/4"x 1/8" tubing and SS-400-6
swagelock union. Fill the lower tube with oil by drawing a vacuum on it
until it siphons out oil from the bottom of the tank.. My preference would
be to put a Nupro valve in each line near the stainless steel plate ( =
bulkhead) so that I could remove the transducers without disturbing the
tank.

Hope This Helps ... Marc
Marc_F_Hult
www.ECOntrol.org