Question

Research and Identify the advantages and disadvantages of Measuring Level using
differential pressure transmitters for both closed and open tanks.

Answer 1

Advantages:

Ø Differential pressure is used to measure level of liquids and liquefied gases in pressurized tanks.

Ø Pressurized tanks are used for a number of reasons like providing a constant output, eliminating foam, providing a barrier for caustic materials, and liquefying gas for easier storage. In all of these scenarios, a differential pressure transmitter is only going to measure the difference between the static pressure and the overall pressure.

Ø The standard hydrostatic pressure formula consists of three variables: pressure, density, and height. The sensor measures pressure, density is input as a constant by the customer, and the height is the product level. For this formula to work, density is key and must remain fairly constant. With a known density and pressure value, the pressure sensor’s electronics can accurately and reliably calculate liquid level from the differential pressure.

Ø Accuracy and consistency have only been improved upon with better sensors and electronics.

Ø Low purchase price

Ø Well known, universal (level, pressure, and

Ø flow) and easily selectable

Ø Broad media compatibility

Ø Unaffected by foam, conductivity or

Ø dielectric constant

Ø No blocking distance

Ø Proven reliability

Limitations:

Ø For starters, installation requires stopping the process and draining the vessel where the measurement is made. This can be a costly or time-consuming process, especially if there are multiple vessels requiring this type of measurement.

Ø The impulse lines and capillary lines used in differential pressure measurements are susceptible to outside influences. If these lines are in high traffic areas, they’re at risk of being crushed, and if outside of a climate-controlled area, lines can heat up or chill, causing a change in material density and a level measurement error.

Ø Measurement affected by density changes

Ø High maintenance for wet legs & re-zero the instrument

Ø Temperatures and changing densities can affect measurement accuracy

Ø Remote seals can be costly for aggressive media applications

Ø Hygienic applications with cold media and hot CIP