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1. If a Radar Level Transmitter Is Inaccurate, Do Not Immediately Recalibrate It
When a radar level transmitter shows an inaccurate value in the field, one common mistake is to immediately change the zero point, full-scale setting, or perform so-called “recalibration.”
For a non-contact radar level transmitter, the factors that actually affect the measurement result usually include:
Abnormal instrument power supply;
Abnormal 4–20 mA loop;
Incorrect empty-tank height or measurement range settings;
Improper installation position;
Incorrect antenna orientation;
Material flow entering the radar beam;
False echoes generated by tank walls, beams, coils, or agitators;
Dust, condensation, or material buildup on the antenna surface;
Inclined material surfaces;
Weak reflectivity of the measured medium;
Measurement entering the near-field blind zone;
Mismatch between PLC/DCS scaling and the instrument measurement range.
Therefore, when troubleshooting an abnormal radar level reading, the first step is to determine whether:
The instrument itself is not operating normally,
or:
The instrument is operating normally but identifying the wrong echo.
These two types of problems require completely different troubleshooting approaches.
2. Step One: Confirm That the Instrument Is Properly Powered
If the radar level transmitter has no display or no output, the power supply should be checked first.
Key points to inspect include:
Whether the DC supply voltage meets the instrument requirements;
Whether the positive and negative power connections have been reversed;
Whether a complete current loop has been formed for a two-wire instrument;
Whether the wiring terminals are loose;
Whether the cable is broken;
Whether the surge protector, safety barrier, or isolator is operating normally;
Whether the PLC analog input is wired correctly;
Whether the loop load exceeds the allowable instrument limit.
For an instrument with a local LCD display, if the local display is normal but the PLC receives no data, the problem is more likely to be in the signal loop, PLC scaling, or communication side.
If the local display itself is abnormal, priority should be given to checking the power supply and the instrument diagnostic information.
3. Step Two: Check the 4–20 mA Output Instead of Immediately Concluding That a Module Is Damaged
Some older troubleshooting information may simply state:
“An output above 22 mA means the display module is damaged, while an output below 3.5 mA means the electronic module has failed.”
This conclusion is not sufficiently rigorous.
Under commonly used NAMUR NE 43 signal conventions, normal measurement information is generally within approximately 3.8–20.5 mA, while values of ≤3.6 mA or ≥21 mA may be used to indicate a fault condition. Whether the device uses a high or low fault current depends on its configuration.
For example:
Around 0 mA: May indicate an open circuit, loss of power, or broken loop;
Below 3.6 mA: May indicate a low fault alarm;
4–20 mA: Normally represents the process measurement range;
Around 20–20.5 mA: May still be within an allowable over-range region;
Above 21 mA: May indicate a high fault alarm.
However, these current values only indicate that the instrument is reporting an abnormal condition. They do not, by themselves, prove that the display module or electronic module is damaged.
The correct approach is to continue checking:
Instrument diagnostic codes;
Echo Curve;
Sensor Status;
HART diagnostics;
Local display alarm information.
4. What Should Be Checked If the Level Changes but the Display Responds Very Slowly?
First, confirm whether an excessively long damping time has been configured.
Radar instruments generally allow parameters such as Damping, Response Time, Integration Time, or similar filtering settings to be adjusted.
The larger the damping value, the more stable the displayed trend becomes, but the slower the response will be.
For example, if the actual level changes rapidly while the trend curve still changes very slowly, check:
Damping inside the radar instrument;
Filtering in the PLC program;
Averaging algorithms in the DCS;
Data logger upload interval;
Cloud-platform display update interval.
The radar itself should not be blamed simply because the cloud-platform trend changes slowly.
If the local instrument display has already changed but the cloud platform refreshes only once every ten minutes, the problem is clearly not at the radar measurement end.
5. What Should Be Done If the Displayed Value Does Not Change at All?
If the material level has clearly changed but the radar reading remains fixed for a long period, check the following in sequence:
5.1 Confirm Which Variable Is Actually Being Displayed
Some systems may display:
Percentage;
Distance;
Liquid level;
Material level height;
Volume;
Historical cached data.
The variable type should therefore be confirmed first.
5.2 Check Whether Output Hold Is Enabled
Some instruments can be configured, after a fault occurs, to:
Hold the last valid value;
Output a fixed high alarm current;
Output a fixed low alarm current.
Therefore, a value that remains unchanged does not necessarily mean that the radar is still measuring normally.
5.3 Check Whether the Echo Has Locked Onto a Fixed Obstacle
Possible fixed targets include:
Cross beams;
Reinforcing ribs;
Heating coils;
Agitator blades;
Tank-wall protrusions;
Filling pipes.
If one of these fixed targets produces a stronger echo than the actual material surface, the radar may continuously track the false target.
In this situation, the echo curve should be checked instead of blindly changing the measurement range.
6. Installation Position Is One of the Main Causes of Inaccurate Radar Level Measurement
A radar beam is not a single straight line. It has a defined beam angle.
Using typical 26 GHz radar as an example, different antenna sizes can produce significantly different beam coverage. Some 25 GHz industrial radar horn antennas have typical beam angles ranging from approximately 19° down to 8°. In general, a larger antenna aperture provides better focusing capability.
Therefore, installation should avoid placing the following objects within the radar beam whenever possible:
Tank walls;
Ladders;
Support beams;
Heating coils;
Agitator shafts;
Temperature probes;
Other instruments;
Incoming material flow.
Installation directly above a strong filling stream is particularly undesirable.
During filling, large amounts of particles, dust, and moving material can generate complex echoes and cause the radar to track the wrong target.
7. Is the Center of a Silo Always the Best Installation Position?
No.
For conical silos, granular-material silos, and bulk-solid applications with a significant angle of repose, the center of the silo may coincide with the filling point, the highest point of the material pile, or an area where complex multiple reflections occur.
The installation position should be evaluated together with:
Filling position;
Discharge position;
Material surface geometry;
Silo height;
Silo diameter;
Internal structures;
Radar beam angle.
For large bulk-solid silos, the fact that the material surface is not horizontal must also be considered.
Therefore, when purchasing a radar level transmitter, providing only “30-meter range” is usually not enough.
8. How Should Antenna Buildup, Condensation and Dust Be Handled?
In applications involving cement, fly ash, mineral powder, grain, animal feed, and similar materials, dust can gradually accumulate on the antenna surface.
Liquid applications may also experience:
Condensation;
Oil contamination;
Foam adhesion;
Buildup from highly viscous media.
A small amount of buildup may not immediately cause a measurement problem, but severe accumulation can reduce the effective echo signal.
For this reason, some industrial radar instruments provide air-purge connections. Industrial bulk-solid radar documentation also commonly specifies air purging for applications involving heavy dust or material buildup.
Recommended corrective actions include:
Inspecting the antenna regularly;
Using an air-purge system suitable for the application;
Adjusting the installation angle;
Selecting an antenna design with better resistance to condensation or buildup.
For corrosive media, any cleaning liquid must first be confirmed as chemically compatible with the antenna, seals, and process connection materials.
Acidic cleaning agents should not be used as a universal cleaning solution.
9. When Should False-Echo Suppression Be Used?
When fixed internal structures cannot be avoided, false-echo mapping or interference-echo suppression can be used.
A typical procedure is to allow the instrument to identify the reflection characteristics of fixed obstacles while the actual material level is known.
However, false-echo suppression should not be treated as:
“The signal is poor, so perform false-echo mapping once.”
Incorrect false-echo mapping may accidentally record the true material surface as interference.
Therefore, it is best performed only when:
The actual liquid or material level has been confirmed;
The measurement range has been confirmed as correct;
The instrument installation position is final;
The internal tank or silo structure is clearly understood.
10. Recommended Field Troubleshooting Sequence for an Inaccurate Radar Level Transmitter
Radar Level Transmitter Troubleshooting Process
Step 1 – Check the Power Supply: Confirm that the instrument starts normally and that the supply voltage, polarity, loop, terminals, barriers, and isolators are correct.
Step 2 – Check the Local Display: Determine whether the instrument itself is measuring normally before investigating the PLC, DCS, or cloud platform.
Step 3 – Measure the 4–20 mA Signal: Distinguish between an instrument-side fault and a control-system-side fault.
Step 4 – Check the Basic Parameters: Verify empty-tank height, full-scale range, engineering unit, zero point, and output direction.
Step 5 – Analyze the Echo Curve: Confirm the position and strength of the true material-surface echo and compare it with possible false echoes.
Step 6 – Inspect the Installation Position: Pay particular attention to the filling inlet, tank wall, support structures, agitators, and other obstacles within the radar beam.
Step 7 – Inspect the Antenna: Check for dust, condensation, material buildup, or other contamination on the antenna surface.
Step 8 – Optimize Parameters if Necessary: Only after the previous checks should false-echo suppression, damping adjustment, or other signal-processing optimization be considered.
This sequence is usually more effective than immediately restoring the instrument to factory settings.
FAQ
Q1: Why does a radar level transmitter suddenly become inaccurate?
A: If the instrument operated normally before and suddenly becomes inaccurate, first check antenna contamination, power supply, wiring, changes in the measured medium, and changes in site structures rather than immediately modifying the measurement range.
Q2: Why is the radar reading much higher than the actual material level?
A: A common cause is that the instrument is identifying a false echo closer to the antenna, such as a cross beam, material buildup, mounting nozzle, or internal tank structure.
Q3: What should be checked if the radar reading is lower than the actual material level?
A: Check the empty-tank height setting, installation reference point, and PLC scaling. Also confirm that the instrument has not locked onto an incorrect echo at a greater distance.
Q4: Why does the instrument barely respond even though the material level is changing?
A: Check the radar damping setting, PLC filtering, and data upload interval. Also inspect whether the echo has become locked onto a fixed target.
Q5: Does a 4–20 mA output above 21 mA mean the radar is damaged?
A: Not necessarily. For devices using a fault-current strategy similar to NAMUR NE 43, a current of 21 mA or higher may represent a fault alarm. The instrument diagnostic code should be read before determining the cause.
Q6: Does a radar level transmitter require regular calibration?
A: For most non-contact radar instruments, routine maintenance focuses less on frequent recalibration and more on checking installation conditions, echo quality, antenna condition, and parameter configuration. The verification or calibration interval should follow the project's quality system and instrument requirements.
Q7: Does heavy dust mean radar cannot be used?
A: No. Industrial radar is widely used for powder and granular material measurement. However, selection must consider measuring range, dielectric properties, dust concentration, installation structure, and antenna type. 26 GHz bulk-solid radar has long been used in high-dust silos containing materials such as cement, raw materials, and animal feed.
Q8: What information does METRAVON require for radar level transmitter selection?
A: It is recommended to provide at least the medium name, measurement range, silo height and diameter, temperature, pressure, dust conditions, filling and discharge positions, internal structures, process connection dimensions, power supply, output signal, explosion-proof requirements, and site photos.
Conclusion
An inaccurate radar level transmitter does not necessarily mean that the instrument is damaged.
In field applications, more common causes include installation position, parameter settings, false echoes, antenna buildup, incorrect range scaling, and signal-loop problems.
Therefore, the correct troubleshooting method is not repeated recalibration, but rather checking the system in the following sequence:
Power supply → output signal → parameters → echo curve → installation → antenna → medium.
For complex applications such as cement, mineral powder, grain, and chemical storage tanks, METRAVON recommends confirming the silo or tank structure and operating-condition parameters during the radar selection stage rather than selecting the instrument only according to measuring distance.
Related resources
Radar level meters · Level measurement
Author: Arvin · Source: METRAVON Instruments
