Rosemount 5401, Справочное руководство

Страница: 173 / 180

Reference Manual
00809-0100-4026, Rev FA
July 2009
C-13
Rosemount 5400 Series
Hold Off Setting
The Hold Off parameter is set to a default value that rarely needs any
adjustment (see “Hold Off Distance” on page C-2 for definition of Hold Off
distance). The Process Seal antenna is slightly more affected by disturbances
in the nozzle than the cone and rod antennas. If necessary, a small Hold Off
adjustment may be sufficient to solve the problem.
In a typical situation, a small object, such as a weld joint, may give rise to a
disturbing echo. If this disturbance is strong enough the transmitter may
misinterpret this echo as the product surface. By setting the Hold Off large
enough to avoid a measurement within and close to the nozzle, the problem is
solved, as illustrated below.
The Spectrum Plot function in Rosemount Radar Master (RRM) allows for
adjustment to the Hold Off distance:
1. In RRM click the Spectrum Plot icon to
open the Spectrum Analyzer window.
2. Select the Configuration Mode tab.
3. Click the Read button and view the
amplitude versus distance graph. If
there is a disturbance caused by an
object in the nozzle, the transmitter
may misinterpret the position of the
surface, as shown to the left. In this
example the true surface position is at
amplitude peak P3.
4. Move the Hold Off distance line away
from the transmitter i.e. to a position
below the nozzle.
5. Click the Store button.
6. The transmitter will now disregard any
disturbing echoes in the nozzle and find
the product surface.
Hold Off
SPECTRUM ANALYZER
Hold Off