Lost Echo Delay (P021) - Emerson Rosemount 3101 Reference Manual

Appendix F: Programming the 3102 and 3105 using HART
February 2015
F.3.27

Lost echo delay (P021)

Fast Keys
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
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
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.
Field Communicator or AMS Device
Manager
To view or change the lost echo delay
1.
2.
3.
4.
5.
Note
When messages appear, take appropriate action if needed and select "OK".
(1) Maximum of 20 seconds.
170
2, 2, 5 [or 6], 1
(page 180) have been received. The output will then change to this new
From the Home screen, select 2: Configure.
Select 2: Manual Setup
Select 5: Engineering (3105) or
6: Engineering (3102).
Select 1: Lost Echo Delay P021.
If a change is required:
(a) Input a new value, and then select "ENTER" to save it.
(b) Select "Send" or "Apply" to update the transmitter.
00809-0100-4840, Rev CB
Lost Echo Delay P021
900 s
900
q w e r t y
a s d f g h
Lock
z x c v b n
Shift
HELP DEL
(Field Communicator Screen Shown)
Programming the 3102 and 3105 using HART
Reference Manual
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