69
Reference Manual
00809-0200-4840, Rev BA
December 2014
Section 4: Configuration
Rosemount 3490 Series Control Unit
To view or change the threshold time:
1.
From the
Main Menu
screen, select
SETUP
.
2.
Select the transmitter (e.g. “
Tx1: 3107
”).
3.
Select
ENGINEERING
.
4.
Select
ADVANCED
.
5.
Select
Thresh 1 Time
.
6.
Follow the on-screen instructions to edit and save a new setting.
7.
Select “
Quit
” to exit to the previous menu.
4.3.30
Threshold 1 size (P048)
False echoes may occur close to the transmitter face. If they occur outside the
Upper Blanking
distance (
), the false echo can be ignored by entering the
echo size
as a percentage and a
duration
(representing distance) for how long this echo size should be ignored. The
echo size
is
set by the parameter
Threshold 1 Size
(
P048
).
See
“Threshold 1 time (P043)” on page 68
for entering the
duration
(representing distance).
Note
In applications where elevated ambient temperatures of around 50 to 60 °C are
experienced, together with poor liquid surface conditions (excessive surface agitation,
foam, etc.) at a high level and within 0.5 m of the transducer face, the transmitter may
see a false echo and report a false high level measurement.
The factory default value of parameter
P048
is 4%.
If the false echo is reported at the end of the
Upper Blanking Distance
(0.3 m or as
adjusted in
P023
), then it is recommended to set the value of
Threshold 1
Size
parameter
P048
to a value sufficient to ignore this false echo.
This should be implemented by reading the size of the false echo (using parameter
Echo Size
,
), and setting the
P048
to a value 4% greater than the reported
value in the parameter
Echo Size
(
Note that this particular approach has an impact on the liquid level reading accuracy
when the liquid level is within approximately 0.5 m of the transducer face. The accuracy
may be reduced from ±2.5 to +2.5/-5.5 mm or, in extreme conditions, +2.5/-8.5 mm.
Use the read-only parameter
Echo Size
) as a reference for the false echo size.
Fast Keys
2, 2, 7, 2, 7
Thresh 1 Time P043
2.9ms
Esc=Quit =Edit
(Rosemount 3491 Screen)
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