What is the suggested orientation of a capacitance level probe that is intended to measure the interface level in a vertical tank and must be installed on the side of the tank?
A. Horizontal
B. 30 degrees above horizontal
C. 45 degrees above horizontal
D. 60 degrees above horizontal
E. Vertical
Installing the probe in the horizontal plane (Answer A) will not measure the tank level but rather function as a level switch by measuring empty below the probe and full above the probe. Installing the probe vertically (Answer E) is not possible on the side of the tank.
The remaining answers (Answer A, Answer B and Answer C) are acceptable, but be sure to calculate the length of the probe needed to measure throughout the desired range of level to ensure that the probe will not hit the opposite wall of the tank.
Additional complicating factors
Specifying the probe to be oriented at 30 or 60 degrees above horizontal appears to be straightforward. However, ensuring that the nozzle is actually installed per specification is not necessarily foolproof because a probe specified to be installed at 30 degrees from vertical could erroneously be installed at 30 degrees above horizontal — greatly reducing the range of level measurement. Such an error is much less likely to occur when the probe is specified to be installed at 45 degrees above horizontal, which is the same as 45 degrees from vertical.
David W. Spitzer is a principal at Spitzer and Boyes, LLC, which offers engineering, focused market research, writing/editing white papers, strategic marketing consulting, distribution consulting, seminars and expert witness services for manufacturing and automation companies. Spitzer has written more than 400 technical articles and 10 books about flow measurement, instrumentation and process control. He can be reached at 845-623-1830 or via spitzerandboyes.com.
