FMP-51 is installed in a co-axcial tank for oil level measurement. Having a empty calibration of 5 meter and Full calibration is at 1.9 meter. When we are feeling oil into the tank level is going down. Some times it is showing some level which is not even correct. Please suggest.

 

>FMP-51 is installed in a co-axcial tank for oil level
>measurement. Having a empty calibration of 5 meter and Full
>calibration is at 1.9 meter. When we are feeling oil into
>the tank level is going down. Some times it is showing some
>level which is not even correct. Please suggest.

I suspect you are getting a false echo. Make sure the in feed is not hitting the probe or the surface is not very disturbed.
Is it possible to enclose the probe in a stilling well to protect it from disturbance?