Common Wiring Problems; Reducing Electrical Noise; Reducing Acoustical Noise; Measurement Difficulties - Siemens SITRANS L 7ML5400 Operating Instructions Manual

Diagnosing and Troubleshooting

11.6 Measurement Difficulties

11.5.3

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.
11.5.4

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.
11.5.5

Reducing Acoustical Noise

• Move the transducer away from the noise source.
• Use a stilling well.
• Install a rubber or foam bushing or gasket between the transducer and the mounting
surface.
• Relocate or insulate the noise source.
• Change the frequency of the noise. Ultrasonic devices are sensitive to noise in the
frequency range of the transducer employed.
• Check that transducer is not mounted too tightly; only hand-tight.
11.6 Measurement Difficulties
If the LOE Timer (2.4.2.) (Page 179) expires due to a measurement difficulty, the Fail-Safe mA
Value (2.4.3.) (Page 179) displays. In rare cases, the SITRANS LUT400 may lock on to a false
echo and report a fixed or wrong reading.
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Operating Instructions, 04/2021, A5E33329501-AG
SITRANS LUT400