Emerson Rosemount 3100 Series, Reference Manual, Page: 132 / 144

Reference Manual
00809-0100-4840, Rev. BA
July 2008
Rosemount 3100 Series
F-18
P041 (Pulse Repeat)
P041 Description
The nominal rate of repetition for ultrasonic pulses from the transmitter is one
pulse per second. If two transmitters were located within the same vessel, it is
possible this would allow ultrasonic pulses from one unit to be received by the
other. If pulses were occurring at the same time, the receiving transmitter
could mistakenly identify this crosstalk as a valid surface echo. This can be
prevented by having both transmitters operate with different rates of pulse
repetition, which means this interference is rejected as not consistent
(pulse-to-pulse).
P041 allows the pulse repetition interval to be adjusted by increments of 0.1
seconds in the range 0.5 to 2.0 seconds, allowing sufficient separation to
avoid crosstalk problems.
Minimum/Maximum value:
“0.5s”/“2.0s”
P042 (Echoes Needed)
P042 Description
The transmitter monitors the echoes returned from the liquid surface or any
other target within range. A valid surface echo exceeds the signal strength
threshold, set by P043 and P048, consistently for more ultrasonic pulse
cycles than set by P042.
The normal value for P042 is 4, meaning four echoes must be received
consecutively from a new, closer surface before this is taken as the actual
liquid level. In addition, surface echoes that are more distant are ignored for
two seconds.
Typically, P042 is used to avoid stirrers, which give occasionally high liquid
level signals when they protrude from the liquid surface. It may also be used
to avoid unwanted input signals from spray, inflows or crosstalk from other
transmitters.
P043 (Threshold 1 Time)
P043 Description
Frequently, false echoes occur close to the transmitter face. If they occur
outside the top blanking distance, the threshold may be maintained at an
artificially high level (size in %) for a programmable duration (in ms).
The programmable duration is set by P043. See “P048 (Threshold 1 Size)” on
page F-19 for the corresponding programmable echo size.
P044 (Target Pulses)
P044 Description
This sets the number of ultrasonic pulses in the burst sent from the transmitter
every second.
The AUTO option allows the transmitter to control the number of pulses.
Minimum/Maximum value:
“4” / “32”