To meet a wide variety of process needs, Penberthy offers: The Model 814 (single-point, line powered), Model 816 (dual-point,
line powered), Model 818 (4-point, line powered), Model 824 (single-point, loop powered), and the Model 828 (4-point, loop
powered). In these types of applications, when the process media rises or falls to a specific point the output of the switch
will change state. Switch outputs can be a 4 to 20mA loop, relay, or a unique optoisolator which provides a "bounceless" solid
state switch closure. The optoisolator combines the advantages of an open collector transistor output with the electrical
isolation you get with a relay; this makes it perfect for use with digital controllers. There are four basic types of level
applications:
Conductive Liquids and Slurries
Materials in this category include: water, acids, caustics, salt solutions, metal ore slurries, any water-based or ionic solution.
An insulated probe should always be used in conductive media. This will allow you to adjust your setpoint over the entire length
of the probe. If the tank is constructed of a non-metallic material, a separate ground reference must be inserted into the
vessel, or a probe with a concentric grounding sheath should be used. Vertical mounting is preferred in most cases, however,
for single-point switches horizontal mounting is preferred .
Insulating Liquids and Slurries
Materials in this category include: oils, most solvents, essentially all hydrocarbons and non-polar liquids and slurries. In
these applications; probe location is critical. The distance from the vessel wall to the probe should be kept at a minimum.
If this isn't possible; a probe with a grounding sheath should be used. Horizontal mounting is recommended when possible (single-point
only).
Granulars
Materials in this category include: grains, crushed stones, any dry, solid product. These applications are similar to "Insulating
Liquids and Slurries," however probe location is even more critical. The "angle of repose" must be considered to determine the
average level point. Also, moisture content is an important consideration. A change in moisture of only 2% to 3% is enough to
make the product act like a conductive material. If you have granulars with particle sizes greater than 4mm, contact Penberthy.
Lastly, probe strength must be considered because of the mass of the media involved.
Liquid-Liquid Interfaces
Essentially all level measurement is an interface -- Vapor - Air/Liquid - Granular. However, Liquid-Liquid Interfaces are special
cases. Of the liquids involved, one must be conductive and the other insulative. The depth of the emulsion layer needs to be
considered. A large emulsion layer can result in poor set point repeatability. For single-point level indication, horizontal
mounting is always recommended.
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