# Level sensor query

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We have an application to measure the level of diesel (DERV) in a bunded storage tank. The height of the tank is 1.83 metres. When the level of the tank reaches 1.83 metres, the tank volume is 79000 litres. Measurement of level will be by a submersible pressure transducer. As these are supplied calibrated in metres H2O, how do I convert the equivalent height of the diesel to give a volume of 79000 litres. TIA

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Divide the height in H2O by the specifioc gravity of the liquid in the tank. If you assume diesel has a S/G of .84 a meter on the transducer would represent 1.22 meters of fuel.

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Not my field at all - but would a sensor(and the cable) intended for use in water be ok to use in diesel?

Also, does not the S/G of diesel vary a lot more with temperature?

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=?UTF-8?B?UGFsaW5kcuKYu21l?= wrote in news: snipped-for-privacy@corp.supernews.com:

Height of water is a standard unit of pressure. I suspect it has nothing to do with the sensor being meant for use in water.

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Maybe you should use anti-explosive and antiflammable components. The diesel shouldn't vary much it density with temperature, so the gfretwell reasoning is precise:

p=ro*g*h, being ro= density, g=gravity constant and h=height. Note that just dividing by diesel density is only valid in case you are considering density of water to be 1kg/dm^3. If you were to use other density units such as pounds/ft^^3. Best regards. Ignacio Simón Yarza Mech&electronics and control eng.

"Scott Seidman" escribió en el mensaje news:Xns96C487FFC6950scottseidmanmindspri@130.133.1.4...

• posted

Thanks for the info.

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Yes Height of Water is a standard of pressure but the important point is -- Is a water sensor suitable to use in the explosive / corrosive environment of diesel oil?

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Is the volume proportional to height? Many fuel tanks have semicircular bottoms and tops. Submerging the pressure transducer to the bottom may be a problem. A good way is to read the pressure in the outlet pipe, provided that the pressure drop due to flow can be neglected.

Jerry

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"John G" wrote in news:4317948c\$0\$524\$5a62ac22 @per-qv1-newsreader-01.iinet.net.au:

Again, nobody said it was a water sensor. It is a pressure transducer. "Water" only has to do with the calibration of the sensor. Of course the sensor you use needs to be appropriate for the environment, but the fact that the calibration is in units of height of water says absolutely nothing about what the suitable environment is.

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Jerry Avins wrote in news: snipped-for-privacy@rcn.net:

The pressure in the outlet pipe will be proportional to the height of the fuel. Physics says your solution suffers exactly the problem you're trying to solve.

I suspect the effects of rounded tops and bottoms will be largely negligible, except at the almost empty and almost full levels.

If you need an exact calculation, you can use a pressure sensor to get height, and use a lookup table to match the volume, or you can weigh the tank.

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What problem is that?

The diesel-fuel tanks for my emergency generators are about five feet long horizontally, with substantially flat ends. The tanks are about 2.5 feet thick, with semicircular tops and bottoms being and flat midsections also about 2.5 feet high, for a total height of about five feet. The volume is the sum of a cylinder and a box, each 2.5 x 5. The rounded parts are not a negligible part of the whole.

2000 gallons is the allowable limit for indoor fuel storage, so the tanks are not completely filled. (They hold about 2100 gallons.) The rest of the reserve is buried outdoors, with heaters to allow it to flow in cold weather. The indoor tank allows time for the outdoor fuel to warm, and provides gravity feed to the turbines (similar to jet engines). We measure fuel on hand, both indoors and out, with a dip stick and conversion table.

Jerry

-- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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Well, I assume the transducer is designed for this hazardous environment.

To convert from meters H2O to another fluid, simply divide the reading by the specific gravity of the fluid. Since diesel is less dense than water, a full tank will not exert as much pressure on the transducer and the signal will indicate a height less than 1.83 meters. But when you take the transducer reading and divide it by the specific gravity of diesel fuel, you correct for this density difference.

daestrom

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Jerry Avins wrote in news: snipped-for-privacy@rcn.net:

ANY pressure sensor, whether sitting on the bottom of the tank as the OP described, or at the outlet pipe, will provide an output proportional to the height of liquid in the tank. The outlet at the tank will give you the same reading, plus an offset for any difference in height, as the bottom of the tank sensor.

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Scott Seidman wrote in news:Xns96C5D1490FBE4scottseidmanmindspri@130.133.1.4:

Ooops, I got it. You're addressing the problem of getting the sensor in the tank. I just thought that would be done through a sealed bung or something.

Been a long week.

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Mount tank with strain gages to get weight:

Tare value when empty - 0

Fill > Scott Seidman wrote:

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One of us misunderstood something.

It is easier to connect the sensor to a tee in the outlet line than to put it into the tank.

If there is a pressure drop in the line due to flow, the reading will be low. That can be avoided with a large diameter line between the tank and the tee, or a separate line for the gauge in which there is no flow.

I understand the physics of pressure head and frictional losses, but I don't know which problem you alluded to.

Jerry

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That's OK. We're singing from the same score now.

Jerry

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...

I think that's the hard way, but in case someone wants to do it, how can the weight/volume relation be nonlinear?

Jerry

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Poster wants LEVEL in a non-linear shape tank!

If you calibrate to LEVEL using the weight, and the cross sectional shape of the tank changes as you add known CALIBRATION amounts to increase level, LEVEL will be non-linear but ALWAYS increasing.

You can get both WEIGHT and LEVEL. The weight/volume relation is linear for a non-compressable fluid.

Gages can be mounted on OUTSIDE tank legs for easier repairs and the use of multiple parallel strain gages is the norm.

Differential pressure gages with lookup is also an option.

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Jerry Av>

• posted

Poster wants LEVEL in a non-linear shape tank!

If you calibrate to LEVEL using the weight, and the cross sectional shape of the tank changes as you add known CALIBRATION amounts to increase level, LEVEL will be non-linear but ALWAYS increasing.

You can get both WEIGHT and LEVEL. The weight/volume relation is linear for a non-compressable fluid.

Gages can be mounted on OUTSIDE tank legs for easier repairs and the use of multiple parallel strain gages is the norm.

Differential pressure gages with lookup is also an option.

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Jerry Av>

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