Emerson Transmitter 350 Mode D’Emploi

The LTM-Series is an assembly of two major 

components:

The Sensor Tube Assembly:  This is a 5/8” diameter 

stainless steel probe, sealed on one end, with the 

magnetostrictive waveguide in its center.  In 

addition to the magnetostrictive waveguide, the 

tube also houses the optional temperature sensor 

and the sensing elements.  The tube is made to 

lengths of 2-30ft. in rigid construction.

The Enclosure and Electronics: The extruded 

aluminum housing has two compartments.  The 

enclosure is rated NEMA 4X and 7.  One side 

contains the microprocessor board assembly and 

calibration push buttons.  The other side contains 

the field wiring termination board.  The electronics 

module is connected to the detector board of the 

sensor tube assembly via a plug-in cable.  The 

electronics module houses printed circuit boards 

(PCB) that encompass surface mount component 

construction utilizing the latest integrated circuit 

technology.

Magtech also has a stainless steel enclosure 

that can be utilized.  Please contact factory for 

further details.

The LTM-250/350 series level transmitters are 

based on the principle of magnetostriction, first 

used for digital delay lines and later precision 

distance or displacement in the machine tool 

industry.  This principle, if designed and applied 

properly, has potentially very high measurement 

resolution, typically better than 0.001 inch.  In the 

machine tool industry such a high resolution is 

desirable.  In the level measurement application, 

however, a resolution of 0.03 inch is more than 

adequate.

In a brief description, the magnetostrictive principle 

consists of a wire extruded and heat treated under 

carefully chosen conditions to retain desired 

magnetic properties, which is pulsed by a circuit 

with a relatively high current pulse.  The high 

current pulse produces a circular magnetic field as it 

travels down the wire at the speed of sound.  

Another magnetic field generated by a permanent 

magnet (the float), placed near or around the wire 

at some distance from the point of entry of this 

pulse interferes with the magnetic field of the 

current pulse and a torsional force results at the 

collision point.

Figure 6. Principle of Operation

The effect of this torsion force is a twist to the wire 

at this point producing torsion wave traveling 

towards both ends of the wire.  The propagation 

time (or time-of-flight) of this wave is measured 

precisely and if the wire properties remain stable, it 

is very repeatable at about 5-10 microseconds per 

inch, which is approximately the speed of sound in 

that medium.  By measuring the exact number of 

microseconds it took the torsion wave to reach a 

designated termination point of the wire, the 

distance to the magnet from this termination point 

can be easily calculated.

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