Emerson Rosemount 3100 Series - P022 (Lost Echo Action; P023 (Top Blanking Distance

Reference Manual
00809-0100-4840, Rev. BA
July 2008
F-15
Rosemount 3100 Series
P022 (Lost Echo Action) P022 Description
This defines what happens to the PV output when a Lost Echo condition
exists, which is after the Lost Echo Delay period (P021) has elapsed.
NOTE
A lost echo is indicated on the Integral Display of the transmitter and
Rosemount 3490 Series Control Unit. It can also be indicated by fault relay.
The selectable options for P022 are “MINIMUM”, “HOLD”, and “MAXIMUM”.
P022 = “MINIMUM”
If this setting is selected, the PV is forced to zero while a Lost Echo condition
exists. In addition, the current on the two-wire loop will decrease to 3.75 mA
(for Rosemount Standard) or 3.6 mA (for NAMUR NE43), depending on the
model order code (see page “Ordering Information” on page A-6).
The current will remain at that level until the correct target echo is recovered.
P022 = “MAXIMUM”
If this setting is selected, the PV is forced to the maximum while a Lost Echo
condition exists. The maximum PV is the value that occurs when an echo is
received from the transmitter face. In addition, the current on the two-wire
loop will increase to 21.75 mA (for Rosemount Standard) or 22.5 mA (for
NAMUR NE43), depending on the model order code (see page “Ordering
Information” on page A-6). The current will remain at that level until the
correct target echo is recovered.
P022 = “HOLD”
If this setting is selected, the current output is held at the last good value.
P023
(Top Blanking Distance)
P023 Description
The Top Blanking Distance defines a zone close the transmitter where an
echo is ignored. Establishing this zone will eliminate echoes from false targets
such as mounting fittings or the end of stub pipes.
P023 defines the vertical distance from the transmitter face to where a valid
surface echo can be detected.
To avoid a false high level alarm, P023 should not be lower than the factory
default.
If P023 is set to a value greater than the Bottom Reference (P010), the
ultrasonic pulses transmission will cease.
If the sum of P023 and P063 is greater than the Bottom Reference (P010), the
ultrasonic pulses transmission will cease.
See Figure F-7 on page F-20 for tank geometry.
Minimum/Maximum value
0.0/999999