59
Reference Manual
00809-0200-4840, Rev BA
December 2014
Section 4: Configuration
Rosemount 3490 Series Control Unit
To view or change the damping:
1.
From the
Main Menu
screen, select
SETUP
.
2.
Select the transmitter (e.g. “
Tx1: 3107
”).
3.
Select
OUTPUT
.
4.
Select
CURRENT
.
5.
Select
Damping
.
6.
Follow the on-screen instructions to edit and save the new setting. (Press the
Enter
(
) key if prompted to change the mode to “off-line”).
7.
Select “
Quit
” to exit to the previous menu.
4.3.21
Lost echo delay (P021)
In pulse echo level measurement systems, ultrasonic pulse echoes are sometimes lost due to
adverse liquid surface conditions such as turbulence or foam. The ultrasonic pulse transmitted
towards the surface is sometimes not returned, deflected away from the transmitter, or
attenuated significantly. In these conditions, the transmitter holds the last valid data and
transmits another pulse to see if the echo is returned.
Lost Echo Delay
(
P021
) defines the period that the transmitter will hold and display the present
valid surface measurement, waiting to update the measurement when the echo is recovered.
A “lost echo” fault condition is signalled if the Lost Echo Delay period ends with no valid echoes
returned.
A valid returned echo occurs inside a 'window' on either side of the liquid level. The 'window'
increases as the range to the target increases. All echoes within the ‘window’ are monitored and
averaged to smooth of the liquid level output under turbulent conditions.
Any returned echo from closer than the liquid surface is considered valid if a minimum required
number of echoes (
) have been received. The output will then change to this new value.
Any echo returned further than the liquid surface and outside the 'window' is ignored. However,
if a lost echo condition is developing and a period
(Lost Echo Delay divided by two
(1)
) has elapsed, any echoes received from further away targets
are treated as valid. The liquid level measured changes to the new value after receiving four such
echoes.
Fast Keys
2, 2, 5, 1
(1)
Maximum of 20 seconds.
Damping P020
3.0sec
Esc=Quit =Edit
(Rosemount 3491 Screen)
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