A level transmitter rarely needs “calibration” in the lab sense — most field fixes are a correct zero/span setup, a clean false-echo map, or a blind-zone that was sized wrong. This guide covers the steps that actually move the reading for 80 GHz radar, ultrasonic and 4G wireless transmitters, and a commissioning checklist you can run on-site.
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For a level transmitter, “calibration” is almost always one of three things — and only the first is a true adjustment of the sensor:
Tell the device where “empty” and “full” are so 4 mA and 20 mA (or 0 % and 100 %) land on the right distances. This is the step people mean by “calibrate”.
On radar, teach the unit which fixed reflections (walls, ladders, welds) to ignore so they stop masquerading as the surface.
Set the measurement window so the sensor never “sees” the nozzle, lid or near-field region it cannot measure.
Wired radar and ultrasonic transmitters output a current loop where 4 mA = empty (0 %) and 20 mA = full (100 %). A HART hand-held or the free PC tool sets the two endpoints:
| Step | Action | Why it matters |
|---|---|---|
| 1. Empty reference | With the tank at a known empty level, set Zero (4 mA) to that distance. | Anchors 0 % to the real empty point, not the antenna face. |
| 2. Full reference | At known full level, set Span (20 mA) to that distance. | Defines the usable range; errors here shift every reading. |
| 3. Loop check | Measure mA at both ends; verify 4.0 and 20.0 mA (±0.05). | A sagging 24 V supply or long cable drops the loop below 20 mA. |
| 4. 2-wire vs 3-wire | 2-wire loops power the sensor from the loop — keep loop resistance < 500 Ω. | Exceeding loop resistance is the most common “20 mA never reached” fault. |
For the exact button sequence on the JJY-YLD128SP radar or JJY-YCD28SPY ultrasonic, see the installation & wiring guide.
Networked units skip the mA loop and speak Modbus over RS485. Calibration here is mostly address and register mapping rather than electrical zeroing:
Set a unique Modbus address per device; match 9600/19200 baud and 8-N-1 on every node on the bus.
Map the level register to engineering units (mm or m). Confirm the high/low register words are in the right byte order.
Fit the 120 Ω terminator at the bus ends only; unterminated or doubly terminated buses drop frames.
80 GHz radar is immune to foam and vapour, but fixed internal reflections still fool it. Two settings decide a clean reading:
Best for Small closed tanks, nozzles, internal ladders and agitators where the beam sees structure, not just the surface.
Watch out False-echo learning must run with the real medium present; learning an empty, clean tank then filling it can reintroduce ghosts.
Teach the unit the fixed reflections at install; it suppresses them and locks onto the moving surface.
Set the near window to the antenna’s dead zone so the nozzle and lid are excluded from the measurement.
Raise it for dusty or low-dielectric surfaces (grain, plastic pellets) so the true echo wins over noise.
These are the same fixes used on difficult vessels in our difficult tanks guide.
Ultrasonic speed-of-sound changes with air temperature, and turbulence throws the beam. Two corrections keep it honest:
Either use the built-in sensor or feed an external PT100; without it, a 20 °C swing shifts the reading by ~3.5 % of range.
In agitated or foaming tanks, a stilling well calms the surface the beam sees and removes the foam error.
Ultrasonic blind zones are larger than 80 GHz radar; keep the max level below the dead zone or the top goes blind.
Run this before signing off a new install:
Antenna centred and plumb; beam path clear of walls, ladders and agitator; dead zone above max level.
Set at real empty/full references; loop reads 4.0 / 20.0 mA (or 0 / 100 %).
Learning done with medium present; ghost peaks suppressed.
Modbus address unique, baud matched; 4G unit reporting to the cloud with correct alarm thresholds.
Compare against a tape or dip at three levels (empty, mid, full); log the deviation.
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