Emerson Rosemount 3100 Series, Reference Manual, Page: 128 / 144

Reference Manual
00809-0100-4840, Rev. BA
July 2008
Rosemount 3100 Series
F-14
P020 (Damping /
Smoothing Time)
P020 Description
This defines the time constant of the exponential smoothing used on the
output Process Value (PV), and is entered as a value in seconds. The pulse
repetition frequency of the transmitter is approximately one pulse per second,
which means that the system response time cannot be faster than this.
Minimum/Maximum value
0.0/9999
P021 (Lost Echo Delay)
P021 Description
Lost Echo Delay is defined uniquely for pulse echo level measurement
systems, where ultrasonic pulse echoes are 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.
The Lost Echo Delay (P021) sets the period that the transmitter will hold and
display the present valid surface measurement, waiting to update the
measurement when the next echo is recovered.
If the Lost Echo Delay period ends with no valid echoes returned, a fault
condition (“LOST ECHO”) is signalled.
• A valid returned echo occurs inside a 'window' on either side of the liquid
level, and the 'window' increases as the range to the target increases.
All echoes within the ‘window’ are monitored and averaged to provide
smoothing of the liquid level output under turbulent conditions.
• Any returned echo from closer to the transmitter than the liquid surface is
considered valid if a minimum required number of echoes (P042) have
been received. The output will then change to this new value.
• Any echo returned further from the transmitter than the liquid surface and
outside the 'window' is ignored. However, if a lost echo condition is
developing and a period (Lost Echo Time divided by two) has elapsed,
any echoes received from further away targets are treated as valid. The
liquid level measured will change to the new value after receiving four
such echoes.
Minimum/Maximum value
0.0/9999