Emerson Rosemount 3100 Series, Справочное руководство, Страница: 137 / 144

Reference Manual
00809-0100-4840, Rev. BA
July 2008
F-23
Rosemount 3100 Series
NOTE:
When the poll address is a non-zero number, the transmitter is in multi-drop
mode and the current output is fixed at 4 mA.
D906 (Current Output)
D906 Description
This displays the current used for the Current Output.
D910 (Target Range)
D910 Description
This gives the distance from the transmitter face to the liquid surface echo
detected. It is a useful diagnostic tool because a false surface signal can be
identified and related to the physical nature of the installation.
D911 (Echo Size)
D911 Description
The size of the echo returned from the liquid surface depends on the surface
range, the turbulence, the presence of foam on the surface, draughts, gas
composition and temperature, the transmitter performance, and other factors.
From pulse-to-pulse, the received echo strength may vary, but monitoring
D911 gives the recorded echo strengths. The value of D911 is an averaged
percentage of the last five echoes, with 100% representing a saturated
returned signal.
D912 (Echo Success)
D912 Description
This is another measure of the quality of the echo returned. It is a percentage
indicating the success rate achieved from the last ten pulse transmissions.
The success rate may fall below 100% due to the effect of extreme surface
turbulence or stirrers, which might return a surface echo that is then rejected
by the transmitter. A surface echo might be rejected because it is outside the
allowed 'window' set-up to establish the liquid level (see “P021 (Lost Echo
Delay)” on page F-14). This rejects invalid readings because liquid levels do
not change very quickly.
One rejected surface echo causes D912 to decrease by 10%, but a
subsequent valid surface echo reinstates this loss. The transmitter is biased
to ignore sudden liquid level changes.
D913 (Target Echoes)
D913 Description
This gives the number of echoes detected by the transmitter. The maximum
number displayed here is seven.
The echo closest to the transmitter face, i.e. the highest liquid level, is used to
calculate the Process Value (PV). This is because the other echoes may be
caused by multiple path surface reflections from tank walls or the roof.
D914 (Speed of Sound)
D914 Description
This is the temperature-corrected speed of sound calculated by the
transmitter. It relates the returned echo time delay to a distance. The value is
calculated using the base value for the speed of sound (P024) and
temperature (D915).