Answer / sam

You said interface level so I must assume you are measuring
oil and water. My experience is on the Khrone BM100 A but
your radar might be similar since the both use TDR technology.
The dielectric constant of crude is about 2 to 4 and water
is 80. The variance in dielectric constant will have a small
effect, so in order to find the right valve one quick way is
to use your sight glass to set the dielectric constants so
that the radar reads the same as the sight glass on the
water and oil. a Good average is normally 2,5 and 80.
Unfortunately this will not work unless you have setup your
Z/S parameters correctly.
If you are still having problems you need to do a complete
setup from scratch. In order to do this you need to get hold
of the design engineer's internal vessel drawings and look
what the calibrated span should be. What you are interested
in is the exact mm measurements from vessel bottom to Z/S
points or positions. From there it is just a matter of
taking exact measurements in the field of your vessel and
your radar installation and make yourself a neat, accurate
detailed drawing to indicate the design spec positions and
the actual position of your probe in relation to the vessel,
and put these measured values in the output 1 and output 2
parameters, keeping in mind zero position is measured from
the probe bottom up and 100% is also from the probe bottom
up and not from zero position up. So if you can see where
the design engineer have said zero should be and you can see
in exactly what position your probe is in relation to those
points it is a matter of calculating how high you need to
measure up from probe bottom to get to those Z/S points
marked by the design engineer. It takes a bit of
trigonometry to do but is easy enough.

Typically these parameters should look something similar to
this. Output 1 (Top product level) 4mA = 150mm, 20mA =
2500mm, Output 2 (Bottom product) 4mA = 150mm, 20mA = 2500mm.
Look strange I know but we have found it is better to set
them both the same instead of trying to set each one to it's
individual span. Both Spans are setup in reference to actual
vessel level %. Interface is also a actual level measurment
in relation to the whole vessel and not to just half the
vessel where for instance to where your wier plate is. If
you do this it will have the effect that you have a very
sensitive interface measurement to a slow level measurment
making your control very difficult. We have done it at one
point and it worked eventually, but it was very difficult to
optimize and get stable control, and even the smallest upset
will cause everything to go crazy again.

In this example the 150mm might be the mm you need to
measure from the probe bottom up to get to the Zero position
of the actual vessel as indicated by the design drawing and
the same with the 2500mm. Obviously just examples. This is
where your exact measurements in the field comes in.
NB!!
Also make sure you have the right probe length in the "tank
Height" parameter and not the real vessel height.
This probe length is normally stamped on the little spec
plate on the head by the supplier.
Good luck!

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