Emerson Rosemount 3308, Reference Manual

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Reference Manual
00809-XXXX-4811, Rev AA
February 2012
Rosemount 3308
A-6
PRELIMINARY
Coating The Rosemount 3308 has a high sensitivity due to its advanced signal processing and high signal to noise
ratio, which makes it able to handle various disturbances. However, the following circumstances should be
considered before mounting the transmitter.
• Single lead probes are preferred when there is a risk for contamination (because coating can result in
product bridging across the two leads for twin versions; between the inner lead and outer pipe for the
coaxial probe)
• PTFE probes are recommended for viscous or sticky applications. Periodic cleaning might be required
• Maximum error due to coating is 1 to 10% depending on probe type, dielectric constant, coating
thickness, and coating height above product surface
Coating on the probe should be avoided since the sensitivity of the transmitter may be decreased leading
to measurement errors. In viscous or sticky applications, periodic cleaning may be required.
For viscous or sticky applications, it is important to choose a suitable probe (see Table A-6 on page A-7).
Bridging Heavy coating that results in product bridging across the two probes for twin lead versions, or between the
pipe and the inner rod for coaxial probes, will cause erroneous level readings and must be prevented.
Single lead probes are preferred in this case. If a Twin Lead probe is required, regular cleaning may be
necessary.
Foam How well the Rosemount 3308 transmitter measures in foamy applications depends upon the properties of
the foam; light and airy or dense and heavy, high or low dielectrics, etc. If the foam is conductive and
creamy the transmitter will probably measure the surface of the foam. If the foam is less conductive the
microwaves will probably penetrate the foam and measure the liquid surface.
Vapor In some applications, as ammonia, there is heavy vapor above the product surface that will influence the
level measurement. The Rosemount 3308 transmitter can be configured to compensate for the influence of
vapor.
CE-mark