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Earthing of level bridle with Rosemount 5300 installed

Hello,

I have faced with one issue regarding a noize in level meter 5300 with 8 mm single rid probe (1.8 m length) installed in 4 inch level bridle. We have a very bad signal quality about 1.5. Level bridle is not smooth inside and have some small roughs. Also the liquid inside has different properties from time to time, but mostly it is a water methanol mixture. In addition the centering disk is not installed. Can it be a reason of low quality? And another question, it is written in manual that level bridle serves as a screen for rigid single probe from outside interference. In this case, are there any earthing recommendations of bridle, for example, jumper between flange of level meter and level bridle and so on.

You can see an echo curve for above mentioned case. Just to resume:

• Probe is rigid single 8 mm.
• Centering disk is not installed.
• Level bridle is 4 inches in diameter.
• Dielectric permeabilty is set for oil based liquids.
• Level bridle is filled with stabilise condensate. The distance from flange bottom to liquid surface is checked with measuring tape and is equaled 650 mm.
• Signal quality is 1.54.

As you see the measurement of level is correct but have some noizes and probe end peak when the bridle is filled. What can be a reason of it?

• Rosemount 5300
• Noize
• Level bridle

Artyom Krot

• 23 Mar 2018 4:23 PM
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1 Reply

• Ingemar Serneby

  

  • 26 Mar 2018 11:29 AM

  Hello Artyom! I highly agree with you; suspecting that the missing centering disc is the major contributor to the noisy signal. Even though it is a rigid probe, the probe may sway inside the cage, causing it to move closer to the cage wall - and this might very well cause the described problems. It is important that the probe is centered within the cage - and with the probe centered, the cage will act similar to the outer tube in a coaxial probe, confining the energy in a similar way. When it comes to "best practice" for grounding, the recommendation is to use the external ground terminal on the transmitter, while the cable shield should only be grounded at the DCS side (and thus not in the instrument itself) - note that "grounding" also depend on local regulations - so here it is important to understand and to follow the local regulations! The conclusion is thus that it is the missing centering disc that is the major contributor for the noise - the good thing is that you can easily retro-fit a centering disc at the end of the probe. Best regards/Ingemar

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