Quiz Corner: Differential pressure level calibration (raw material storage tank)

May 17, 2024
Do you have the right answer? Check out the latest installment of Quiz Corner to find out.

Level instrumentation is required for a new vertical raw material storage tank that is 3 meters in diameter, 10 meters high, and open to the atmosphere. The specific gravity and viscosity of the raw material are 1.00 and 250 cP, respectively. The tank sits on a concrete slab and its top is flat. Which of the following are reasonable calibrations for the new differential pressure level transmitter?

  1. 0 to 10 meters of water column
  2. 0 to 9 meters of water column
  3. 0 to 3 meters of water column
  4. 1 to 10 meters of water column
  5. 1 to 9 meters of water column

Differential pressure level transmitters for this type of application usually incorporate an integral diaphragm seal on the high-pressure side of the transmitter large enough to mitigate plugging. Sometimes, the diaphragm seals extend into the tank to eliminate voids that can solidify. Determining a reasonable calibration involves establishing the elevations of the level transmitter nozzle and hence, the transmitter.

Physically locating the level transmitter on a nozzle at the bottom of the tank is physically difficult, and can create a tripping hazard, but would result in a calibration of 0 to 10 meters of water column (Answer A). Answer D implies that the transmitter is at the bottom of the tank, the tap is at 1 meter and results in similar physical difficulty in addition to possible plugging. Answer E suggests that the transmitter is at 1 meter and is connected to a nozzle at 2 meters, which is possible but, like Answer D, is not recommended. Answer C seems to reflect the tank diameter, which has no influence on the calibration.

In practice, the level transmitter nozzle would likely be located approximately 1 meter above the bottom of the tank, so the calibration would be 0 to 9 meters of water column (Answer B) which would be reasonable.

Additional complicating factors

The problem statement states that this tank requires level instrumentation. Even though the level transmitter can generate a high-level alarm, regulations and good engineering practice often dictate the installation of an independent high-level switch to help prevent the tank from overflowing by sounding an alarm and sometimes taking action, such as closing a fill valve or turning off a pump. The high-level switch generally should not utilize the same measurement technology as the level transmitter.

About the Author

David W. Spitzer

David W Spitzer’s new book Global Warming (aka Climate Change): An Understandable Data-Driven Explanation and Pathway to Mitigation (Amazon.com) adds to his over 500 technical articles and 10 books on flow measurement, instrumentation, process control and variable speed drives. David offers consulting services and keynote speeches, writes/edits white papers, presents seminars, and provides expert witness services at Spitzer and Boyes LLC (spitzerandboyes.com or +1.845.623.1830).

Sponsored Recommendations

Learn About: Micro Motion™ 4700 Config I/O Coriolis Transmitter

An Advanced Transmitter that Expands Connectivity

Micro Motion™ G-Series Compact, Drainable Coriolis Flow and Density Meters

Micro Motion G-Series Coriolis flow and density meters are ideally suited for Process Monitoring and Optimization applications, offering easy selection with pre-selected models...

Learn about: Micro Motion G-Series Coriolis Flow and Density Meters

The Micro Motion G-Series is designed to help you access the benefits of Coriolis technology even when available space is limited.

Micro Motion 4700 Coriolis Configurable Inputs and Outputs Transmitter

The Micro Motion 4700 Coriolis Transmitter offers a compact C1D1 (Zone 1) housing. Bluetooth and Smart Meter Verification are available.