How to Map a Radar Level False Echo
False-echo mapping teaches a radar level transmitter to ignore the fixed reflections in a vessel, nozzles, ladders, agitator shafts, pipes, so it locks onto the real liquid surface and not a piece of steel. It is one of the highest-value steps in radar commissioning and one of the most commonly botched, because a map run at the wrong level records the wrong things. This guide walks running a false-echo map properly, from getting the vessel low through recording the fixed echoes to confirming the transmitter now tracks only the surface.
Map a Radar Level False Echo in one line: To map a radar level false echo, get the vessel as empty as you safely can so the fixed reflectors are exposed, then run the transmitter's false-echo or interference scan to record the reflections from nozzles, structure, and the tank wall over that empty range. The transmitter stores this map and suppresses those fixed echoes, so it tracks only the true liquid surface. Mapping at too high a level bakes real surface echoes into the map and causes dropouts later.
Get the Vessel as Empty as Possible
A false-echo map records whatever reflections exist over the range it scans, so it must be run with the liquid surface as low as you can safely get it, ideally below all the fixed reflectors you want to suppress. If the vessel is drained, every nozzle, weld, ladder, and internal structure above the liquid is exposed as a fixed echo the transmitter can learn to ignore. Run the map over the range from the antenna down to just above the current low surface, so you capture the structure without recording the liquid itself.
This is the step people rush, and the cost is high. Mapping with the vessel part-full records the actual liquid surface as if it were a fixed reflector, so later, when the real level moves away from that height, the transmitter suppresses the true surface there and drops out. Getting genuinely low first is the whole discipline. The false echoes you are suppressing are the fixed reflections described in radar level false echo, which compete with the surface return.
Run the Interference Scan
With the vessel low, start the transmitter's false-echo mapping function, variously called an interference scan, tank map, or empty-spectrum recording. The transmitter sweeps its measuring range, records the amplitude and distance of every stationary reflection it sees, and builds a stored profile of the fixed clutter. Tell it the current true level or the extent of the empty range so it does not record beyond the exposed structure into the liquid. The result is a map the firmware subtracts from every future measurement.
Set the map to cover the range where false echoes actually live, typically the upper portion of the tank around the nozzles and internal structure, without extending into the region the liquid normally occupies. On a vessel with an agitator or heavy internals, the map is doing real work and is essential to a stable reading. This mapping is a routine part of commissioning any radar level transmitter in a cluttered vessel, and it is far more effective than trying to filter the resulting confusion downstream.
Confirm the Transmitter Tracks the Surface
After mapping, look at the echo profile and confirm the picture is clean: the fixed reflections you recorded should be suppressed, and the transmitter should be locked onto the single moving surface echo. If a false echo still competes, either it was not captured, because the level was too high during mapping, or it is intermittent and not truly fixed, such as a moving agitator blade, which mapping cannot fully handle. Rerun the map lower if fixed echoes remain unsuppressed.
Then move the level and watch the transmitter follow. As the liquid rises and falls through the mapped region, the reading should track the true surface smoothly without jumping to a suppressed echo or dropping out. A reading that dropps out at a specific height is the classic sign of a surface echo accidentally baked into the map at that level, which means the map was run too high and must be cleared and redone. A clean track through the full range is the proof the map is right.
Verify and Maintain the Map
Verify the mapped transmitter against a hand dip, because a radar that tracks smoothly can still be locked onto the wrong echo and read a consistent wrong value. A dip that agrees confirms the transmitter is following the real surface, not a mapped or false one. Do the check at more than one level to confirm it tracks correctly across the range, especially through the region where the fixed reflectors sit.
Treat the map as maintainable, not permanent. If internal structure changes, an agitator is modified, a heating coil added, or heavy deposits build on a nozzle, the fixed-echo picture changes and the old map may no longer suppress the right things, causing new false locks. When the level feeds a monitoring history, a map going stale often shows as intermittent jumps or dropouts appearing at specific levels where none existed before, prompting a fresh map on the next low vessel. The trend flags the new behaviour; a re-map on an empty tank restores clean tracking.
Avoid the Common Mistakes
The defining mistake is mapping with the vessel too full, which records the real surface as a fixed echo and causes dropouts when the level later moves off that height. Others are mapping over a range that does not reach the actual reflectors, leaving them unsuppressed, and trying to map out an intermittent or moving reflector, which a fixed-echo map cannot handle. And forgetting to verify against a dip, so a smooth but wrong lock goes unnoticed.
Because a bad map produces problems that appear only at certain levels, the fault can look like an intermittent transmitter glitch and send people chasing the wrong thing. Trending the level and noting where jumps or dropouts occur in a monitoring platform points straight at a map issue when the trouble clusters at specific heights. The history localizes the problem to a level; clearing and rerunning the map on a genuinely low vessel is the fix.
Frequently Asked Questions
When should I run a radar false-echo map?
Run it during commissioning with the vessel as empty as you can safely get it, and rerun it whenever the internal structure changes or deposits build up enough to alter the fixed reflections. The vessel must be low so the map records the nozzles, ladders, and structure rather than the liquid surface. Mapping on a part-full tank records the real surface as fixed clutter and causes dropouts later, so getting genuinely low first is essential to a valid map.
Why does a radar level drop out at one specific height?
The most common cause is a false-echo map that was run with the vessel too full, which recorded the real liquid surface at that height as if it were a fixed reflector. When the level later returns to that height, the transmitter suppresses the true surface echo there and drops out. The fix is to clear the map, get the vessel genuinely low, and rerun the interference scan so it captures only the fixed structure and not the liquid surface.
Does false-echo mapping fix a reading that jumps with an agitator running?
Only partly. Mapping suppresses fixed, stationary reflectors like nozzles and structure, but an agitator blade or a moving shaft is not stationary, so a fixed-echo map cannot fully remove it. If the noise correlates with the agitator running, the surface is genuinely disturbed and the better fixes are a stilling well to shield the beam, modest damping, or a technology suited to agitation, rather than expecting the false-echo map alone to handle a moving reflector.
Automation services
Need help turning this into a working system?
Merobix integrates SCADA, programs Allen-Bradley and Siemens PLCs, and designs and fabricates industrial control panels.
Meeting requests are reviewed before confirmation.