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Rosemount Radar Level Transmitter 5402 no signal

We have a 5402 LT without its cone antenna installed and it was working perfectly.

But later, after few years, it started giving a BAD signal.

It is mounted on a flange with 2 inches pipe under.

We did not installed the 2-inch cone antenna because it doesn't fit into the 40mm hole of the flange.

The pipe length under the flange is 530mm.

The tank height is 1500mm.

Total height of the LT from the "0" ref (bottom level of tank) is 1500mm + 530mm = 2030mm.

My questions are:

1. Is it because the cone antenna is not installed that's why it is giving a BAD signals now?

2. Can we retrofit the LT with a rod antenna? If yes, what are the things need to consider to retrofit the rod?

Thanks for your responses.

6 Replies

  • Hello! The antenna is there for a good reason and that is to convey and to focus the microwaves in a controlled manner. Without the antenna, the pipe will in this particular case act as one, but with very unpredictable result. It is rather similar to when you have a bare bulb without reflector in your flashlight. One reason why the radar have worked for a while might be that the assembly was clean in the beginning and that you now have an extent of build-up and/or condensation that is causing disturbances in the assembly. If then the threshold settings are too narrow set, the radar will most certainly give a bad signal. When it come to the antenna, the rod antenna will not fit the 5402 as it is designed for a much lower frequency, further a rod antenna is a very bad fit in a pipe or a tall nozzle, so it would not help to use a lower frequency radar here either. My best antenna recommendation is to cut an ordinary cone antenna to fit into the pipe, with a minimum gap between the antenna opening and the pipe wall. If you cut the antenna manually; please make sure to make a clear and precise cut.
    However, the above is based on the assumption that the erratic bahaviour is caused by a combination of a missing antenna, too narrow threshold settings and contamination. Only when we have more details from the actual gauge, we will know for certain - and such details would be plots from the unit, where we can see the echo curve, a backup of the database and also a visual inspection of the unit. I thus highly recommend you to contact your local Emerson service engineer to get assistance with interpreting the data from the unit and thus find out a suitable solution.
  • Thanks Ingemar.

    What if we get a new 5401 flange-type rod antenna LT and cut our nozzle to about 100mm height? Is this the best solution? Tank height is 1500mm, excluding the 100mm nozzle.
  • In reply to Rein:

    Hello Rein,
    I believe that you can use the existing radar with a cut-to-fit cone antenna as your primary solution. Still, we need to see tank plots from the device in order to give you our best recommendations. In general, the 5402 should work fine on the nozzle, given that it is clear cut and free from obstacle - also this we can see in the tank plots from the device. We do not recommend you to use the rod antenna here. Are you familiar with how to save tank plots from the device? If not; please let us know so we can provide you with instructions. Please also let us know if you already are in contact with an Emerson service engineer, or want us to connect you to the service organization in your world area? In such case; where are you located?
    Best regards,
  • In reply to Ingemar Serneby:

    Thanks again, Ingemar.

    But if that cut-to-fit cone antenna did not work, which among the 4 options below do you think is the best solution?

    OPTION 1: Increase the hole size on the mounting flange so that the extended cone antenna can enter.

    OPTION 2: Cut-to-fit the cone antenna.

    OPTION 3: Use 5401 rod-type antenna and cut the nozzle height to 100mm.

    OPTION 4: Use the cut-to-fit antenna of 5402 and cut the nozzle height to 100mm.

    Or any other suggestions/options?

  • In reply to Rein:

    If possible, I would propose to cut the nozzle and use a cone antenna that is cut to fit (option 4) as my first priority. If it is not possible to cut the nozzle, I would propose an extended cone antenna (option 1). Such extended cone antenna need in such case to be ordered from factory as a "special". The third best solution is the easiest; to install a cut to fit cone antenna in the existing nozzle (option 2). This will likely work fine if the nozzle is clean, without obstructions - and it will be relatively easy to make a trial with this solution.
    So: From a technical viewpont, the best solution is option 4, followed by option 1 and then by option 2.
    From practical reasons I would however recommend you to first try option 2 before you go ahead and cut the nozzle as this very well might be a working solution. The fact that the unit has been in operation for a longer period of time without any antenna at all, implies that option 2 very well will work fine.
    Still: It would be really good to see some tank plots from the unit to rule out the possiblility that something is wrong with the unit itself.
    Best regards,
  • In reply to Ingemar Serneby:

    Thanks, Ingemar. We'll do as you have said and let you know the result.