Measuring volume of bulk chemicals

refer to the manufacturer's calibration instructions for the instrument. We do not know from your post what kind of instrument you are calibrating. If it is a 'DP' cell, it works by measuring the hydrostatic head, which is a function of liquid height and specific gravity.

Basically one adjusts the span of the instrument so the output is '5' ma when the tank level is '0" and 20 ma when the tank is full--assuming it is a '5-20 ma' device. That is done by applying a calibrated air pressure to 'simulate' the calculated hydrostatic head at the full height. The reason a 5-20 ma range is used instead of '0-20' is a '0' is not conclusive-it could be either 0, or non-functioning.

Hi Keith Thanks for your reply. I apologise for not being clear in my question. I know how to calibrate the sensor, what I need to know is how much Sodium Bisulphite will be in the tank when its full. The old indicators go up to 25 tonne (Hydrogen Peroxide). According to the guy who works around the chems, he thinks it contains about 32 tonnes of Sodium Bisulphite. I need to know how to accurately calculate the scaling so I can display an accurate readout to the users and on the DCS. Regards John

Are you interested in knowing the level or the quantity?

If it's just level, you just empty the tank and zero the instrument, then fill the tank and span the instrument.

If you want quantity, you'll need to know the density of the fluid. When you have that, you can infer the quantity when you measure the level.

Yes, it's the quantity that I am after. I am however unfamiliar with the calculations required to scale for this chemical. The density of Sodium Bisulphite is 1.48 g/cm3 Regards John

Basically, you'll just need to know the volume of your tank (between the 0 and 100% level points). Say, if your tank is 100 m³, each 1% of your level is equivalent to 1 m3. You already know the weight per unit volume so calculating the total weight of product in the tank is easy.

If your tank is spherical, however, the relationship won't be linear. You'll have to use a formula which I don't have with me right now. I'm on vacation .

If you want, you can also compensate for temperature since density varies with temperature. I don't have formulas for that though.

If the density of the Sodium Bisulfite is 1.48 g/cm3, you can use a ratio formula to find the volume of the hydrogen peroxide and multiply that times the known volume of the HP. For instance, if the volume in the tank is 25 tons of HP and you know the density of that, simply apply the following formula:

D1/D2 = V1/V2 Where D1 is the density of the HP and D2 is the density of

the SB and V1 is the weight of the HP and V2 is that of the SB.

This will give you the weight of the same VOLUME of the two substances. Since your meter caklculates in weight, you should have some provision in the apparatus to input the density of the substance you are considering.

You say that you can measure the exact volume of the tank. Do that, and then multiply the density (gm/cubic cm )by the volume (cubic cm) to get the weight (in grams).

If you are having trouble with the unit conversions, there are many sites on-line to do that. One I use frequently is at refdesk.com.

Thanks guys, thats exactly what I needed to know.

I had considered that, but thought it may be too simple, and there may be some important step that I would miss, making my scale all wrong.

Cheers

For Pete's sake,as an active field engineer-- did you not take physics and/or chemistry in high school?.............Volume of a cylindrical tank is calculated by the simple equation: pie r squared times height............This should be an expression imprinted within your mind as well as the weight of one gallon of water @8.34lbs/gal and atmospheric pressure @14.7psi (not gauge)...... Should be like breathing