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Radar Level transmitter 5400 - Weak strength signal

Dear All

We have problems with two level transmitters 5400. During a day "Strength Signal" can change from 6000 mV to 150 mV.

When "Strength Signal" near 150 mV transmitter loses a level time to time. It happens every day.

We've done:

1. Reset the transmitter to a default settings and reconfigured it.

2. Cleaned the antenna many times.

3. Checked a connection between a flange  and a transmitter head - no moisture and dirty.

4. Tried different configurations  - the same situation (foam, turbulent, foam + turbulent , different the "Product dielectric", different  the " Tank type" ).

5. Tried different  thresholds from 400 mV to 50 mV, but the transmitter loses a level time to time.

Conditions:

1. The walls of the tank are made of concrete.

2. The high of the tank is 4600 mm

3. The tank contains produced water from a refinery plant.

4. We don't use a stilling well.

On the tank we have two level transmitters 5400 and their behavior is the same.

What can we try more? 

Below are screenshots of transmitter:

5 Replies

  • Dear Sergei,
    In order to fully understand the problem and thus in order to give you our best guidance, we would like to know more about your observations, such as;
    - You state that you have cleaned the antenna several times. Was the antenna dirty or covered with condensation? Did the cleaning improve the situation? What was the signal amplitude before and after cleaning?
    Solution: If the problem is caused by condensation, the best way to avoid this is to either insulate the radar nozzle or heat-trace it. This is in order to avoid a cold spot where the condensation will build up.
    - You state that you have tried several process conditions settings (turbulence, foam and both combined) without any improvement. Do you know whether those process conditions may occur in real life? If you for instance experience severe turbulence or foam or both right under the radar due to that the radar is situated above a filling inlet, it is recommended to find a better position for the radar, as such filling inlets can create such severe tank conditions that makes it hard for the radar to detect any Surface, regardless of software settings.

    The radars seem to work well between the occasions when they lose the signal; the 6000mV signal strength is what to expect from this kind of applications and thus an indication that the radars are healthy: Nevertheless, the signal drop to 150mV is definitely not normal! In order to assist you further with this matter, we would thus need your further assistance with the following questions:
    - Have you observed build-up of condensation or dirt (or both) at the antenna?
    - Are there anything located under the radar that may cause turbulence or foam (such as filling inlets and similar)?
    - What are the process conditions (can there be turbulence, foam, calm surface, oil floating on top of the surface)?
    - Where is this site located? Have you been or are you in Contact with the local Emerson office regarding this issue?

    Looking forward your reply and to assist you further with this matter!
    Best regards,
    Ingemar
  • In reply to Ingemar Serneby:

    Dear Ingemar Serneby,

    - Have you observed build-up of condensation or dirt (or both) at the antenna?
    We found build-up of condensation every time when we cleaned, but without any dirt.
    - What are the process conditions (can there be turbulence, foam, calm surface, oil floating on top of the surface)?
    The process condition is calm surface with oil floating on top of the surface. I know about conditions like turbulence and foam, but I setting it up as an experiment, the transmitter becomes a little stable, however, it sometimes loses a level ("Strength Signal" goes to 150-300 mV)
    - Where is this site located? Have you been or are you in Contact with the local Emerson office regarding this issue?
    Iraq, I didn't contact with them.
  • In reply to Sergei:

    Dear Sergei,
    It seems to me as the main resaon for the problem is condensation at the antenna. Is the radar installed on a nozzle or did you use a bracket mount? I assume that this is kind of a sump type of vessel. I also assume that this is a 5402 type of radar (the higher frequency of the two 5400 radar models) - in such case, a parabolic antenna would be much less sensitive to the condensation - even though it is normally a "too good" antenna for this kind of applications - if you are unable to either heat the nozzle or purge the existing antenna with compressed air. If this site is Cold during nights and hot during the days, the condensation will evaporate and get trapped in the sold spot. Solution is thus to maintain the antenna (the cold spot) clean from condensation - or; to replace to another antenna that is less sensitive to it (i.e. the 8" parabolic antenna - if there is space enough). Our newer non-contacting radar, the 5408, is much better suited for this application, especially with its process seal antenna - and that might be the solution if nothing else will resolve this.
    Best regards,
    Ingemar
  • In reply to Ingemar Serneby:

    Dear Ingemar Serneby,
    The radars installed on nozzles and they worked many years perfectly. We have several vessels like this with two level transmitters on each (the same transmitter), but problems came only on this vessel in this year, of course, it can be led some degradation inside nozzles. We can't use parabolic antenna - it isn't enough space.
    We'll try eliminate condensation. Thank you for your suggestions!
    I have one question more - If I find 5401 transmitter, will it more suitable?
    The 5401 transmitter is low frequency that less affected by condensation as I know.
  • In reply to Sergei:

    Dear Sergei,
    You are most likely right about the nozzle degradation - especially if the nozzles are made out of carbon steel. You are also right about that the 5401 is a better fit due to its lower frequency - or a 5408 with its process seal antenna and ultra high signal-to-noise ratio.
    Best regards,
    Ingemar