Non-Transducer Noise Sources; Common Wiring Problems; Reducing Electrical Noise - Siemens SITRANS LUT400 Operating Instructions Manual

Acoustical Noise
To confirm that the problem is acoustical, place several layers of cardboard over the face
of the transducer. If the noise is reduced, the noise is definitely acoustical.

Non-Transducer Noise Sources

Remove all input and output cables from the SITRANS LUT400 individually while
monitoring the noise. If removing a cable reduces the noise, that cable may be picking up
noise from adjacent electrical equipment. Check that low voltage cables are not being
run adjacent to high voltage cables or near to electrical noise generators such as variable
speed drives.
Filtering cables is an option but is not recommended unless all other options have been
exhausted.
The SITRANS LUT400 is designed to work near heavy industrial equipment such as
variable speed drives. Even so, it should not be located near high voltage wires or switch
gear.
Try moving the electronics to a different location. Often moving the electronics a few
meters farther from the source of noise will fix the problem. Shielding the electronics is
also an option, but it should be a last resort. Proper shielding is expensive and is difficult
to install properly–the shielding box must enclose the SITRANS LUT400 electronics
completely, and all wires must be brought to the box through grounded metal conduit.

Common Wiring Problems

• Make sure that the transducer shield wire is connected at the electronics end only.
Do not ground it at any other location.
• Do not connect the transducer shield wire to the white wire.
• The exposed transducer shield wire must be as short as possible.
• Connections between the wire supplied with the transducer, and any customer
installed extension wire should only be grounded at the LUT400.
On Siemens transducers the white wire is negative and the black wire is positive. If the
extension wire is colored differently, make sure that it is wired consistently.
Extension wire must be shielded twisted pair. See the installation section for
specifications.

Reducing Electrical Noise

• Ensure that the transducer cable does not run parallel to other cables carrying high
voltage or current.
• Move the transducer cable away from noise generators like variable speed drives.
• Put the transducer cable in grounded metal conduit.
• Filter the noise source.
• Check grounding.
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