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Reference Manual
IP2048/RM, Rev AA
Appendix F: Configuring Using HART
February 2015
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 (page 136) have been received. The output then changes 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.
Field Communicator
To view or change the lost echo delay:
1. From the Home screen, select 2: Configure.
2. Select 2: Manual Setup
3. Select 5: Engineering (MSP900GH)
or 6: Engineering (MSP400RH).
4. Select 1: Lost Echo Delay P021.
5. If a change is required:
(a) Input a new value, and then select “ENTER” to save it.
(b) Press “SEND” to update the transmitter.
Note
When messages appear, take appropriate action if needed and press “OK”.
Mobrey MCU900 Series control unit
To view or change the lost echo delay:
1. From the Main Menu screen, select SETUP.
2. Select the transmitter (e.g. “Tx1:MSP400RH”).
3. Select ENGINEERING, and then select LE Delay.
4. Follow the on-screen instructions to edit and save the new setting.
(Press the Enter ( ) key if prompted to change mode to “off-line”).
(1) Maximum of 20 seconds.
Lost Echo Delay P021
900 s
900
ESC
DEL ENTER
HELP
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(Field Communicator Screen)
LE Delay P021
900sec
Esc=Quit =Edit
(Mobrey MCU901 Screen)