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Comparing Displacer Level Transmitter and Differential Pressure Transmitter Technology

Level measurement in the process industry is typically accomplished using a variety of technologies. Although the industry is continually innovating, many level applications are still regulated using older technology. One of these older technologies commonly used in the process control industry is the differential pressure (DP) level transmitter, which first was introduced in the 1950s. It measures the hydrostatic head pressure of a liquid in a vessel and converts this to a level measurement, based on an input specific gravity/density of the liquid.

A newer technology that is also dependent on specific gravity is the displacer level transmitter. Changing buoyancy forces caused by liquid level change act upon the spring-supported displacer, causing vertical motion of the core within a linear variable differential transformer (LVDT). As the core position changes with liquid level, voltages are induced across the secondary windings of the LVDT. These signals are processed in the electronic circuitry and converted to a useable output signal. The enclosing tube acts as a static isolation barrier between the LVDT and the process media. Magnetrol® manufactures a displacer level transmitter called the E3 Modulevel®, an advanced, intrinsically safe two-wire instrument.

There are significant differences between displacer level transmitters and differential pressure transmitters, which affect the installation, maintenance, and accuracy of the level transmitter chosen. Displacer level transmitters can improve process performance in a wide range of applications, offering significant advantages over differential pressure transmitters in several areas, including:

  • Calibration
  • Temperature range
  • Mounting
  • Installation cost

MAGNETROL has produced a white paper that outlines the benefits of displacer level transmitter technology over differential pressure transmitters, including a side-by-side comparison chart. To learn more about these transmitters, download the white paper.