Abstract: A redundant level measuring system comprises a chamber for fluidic coupling to a process vessel whereby material level in the vessel equalizes with material level in the chamber. A float including a magnet in the chamber rises and falls with material level in the chamber. A magnet actuated visual indicator is mounted to the chamber for indicating level of the magnet in the chamber. A measurement instrument includes a probe and a measurement circuit. The instrument is mounted atop the chamber with the probe extending downwardly into the chamber. The measurement circuit measures a characteristic of the probe representing level of the material in the chamber. A shield in the chamber isolate the float from the probe.

Abstract: A redundant level measuring system comprises a chamber for fluidic coupling to a process vessel whereby material level in the vessel equalizes with material level in the chamber. A float including a magnet in the chamber rises and falls with material level in the chamber. A magnet actuated visual indicator is mounted to the chamber for indicating level of the magnet in the chamber. A measurement instrument includes a probe and a measurement circuit. The instrument is mounted atop the chamber with the probe extending downwardly into the chamber. The measurement circuit measures a characteristic of the probe representing level of the material in the chamber. A shield in the chamber isolate the float from the probe.

Abstract: A dual compartment housing has a wiring compartment containing customer accessible wiring board and openings for a conduit connection. The wiring compartment is separated from an electronics compartment by a tunnel. The tunnel, which can be potted with a sealing compound, provides environmental and explosion proof protection for the electronics. An intrinsically safe barrier can be housed in the explosion proof wiring compartment, and the electronics compartment is then intrinsically safe. This relieves any constraint on separating the intrinsically safe electronics exposed to the process by an explosion proof boundary, and the process seal can be a "soft" seal. The housing is designed so that both compartments face the same direction.

Abstract: A point level sensor senses capacitance of a material in a vessel to determine level. The capacitance is input to a comparator which is part of an oscillator circuit developing a square wave signal having a period corresponding to capacitance. A microprocessor includes an internal counter which determines the period of four pulses to determine an average period. The microprocessor drives relay circuits providing discrete outputs according to specific precalibrated levels to be sensed. The point sensor includes a self-test mode which operates once per second to test for shorting of the probe, expected frequency response and an open probe.