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EHELP: How do I account for the linearization function representing the volume measurement in a cone-shaped bottom tank at various levels?

EHELP: How do I account for the linearization function representing the volume measurement in a cone-shaped bottom tank at various levels?

Q.  We want to use a SPD Field-Mount Programmable Loop Display with a radar transmitter mounted on the top of a cone-shaped bottom tank that outputs 4-20mA signal, and we would like to know how to account for the linearization function representing the volume measurement in the tank at various levels?

A. There are several things you can do depending on what information you have regarding your tank. Some tanks come with a strapping chart and the chart will tell you what volume you have at different levels inside the tank.

In this case, you can load a list of ordered pairs in a CSV (comma separated value) format into the SPD. Alternatively the SPD configuration software allows you to import a CSV (comma separated value) file that represents your linearization table, from Microsoft Excel for example. The SPD allows for custom curves using up to 128 linearization points.

If you do not have a strapping chart, you will need to do some math to relate the level in the tank to the tank volume based on the geometric shape(s). For example, at 5 inches you may have 5 gallons, and at 8.5 inches, you might have 10 gallons. If you have a vertical cylinder on top of a cone, the calculations should be relatively easy. A more difficult calculation would be a horizontal cylinder with F&D (flanged & dished) heads and with various nozzles.

The SPD is an excellent choice as a programmable field-mount loop indicator with extra-large 5-digit display that has large 29mm (1.15 in) digits for long-distance viewing and can be ordered with a back-lit option. The optional back-lit display makes it easy to read in dark conditions. Superior accuracy allows the SPD to display process information ±0.012% of input scale, it can operate in ambient conditions as low as -40°F, and a standard SPD is loop-powered by less than 2.3 volts (2.3VLP power input module). The SPD is also programmable with supplied configuration software to display a percent or any other engineering unit (EGU) of up to 5 characters.

Find out more about the SPD.

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Published: April 12, 2017
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