Most radar level transmitter problems are solved at the installation and wiring stage, not by returning the unit. This guide walks through commissioning, beam-angle clearance, power cabling, 4–20 mA calibration, RS485 addressing and PC-connection steps for our 80GHz FMCW radar level transmitters (wired and 4G models, accuracy down to ±1 mm on wired units, IP68 housing).
If your symptom is unstable or false readings rather than a wiring/ calibration issue, start with the echo & signal diagnosis guide; difficult vessels (silo, narrow pipe, small metal tank) are covered in the difficult-tanks guide.
A radar cannot measure correctly until two things are set: the installation height (vertical distance from the tank bottom to the radar hemisphere) and, for 4–20 mA models, the current calibration. Mount the antenna perpendicular to the surface and keep the beam clear of obstructions. Full commissioning checklist: can the radar be used directly after installation?
The 80GHz beam is about ±2.75° — it cannot be made narrower without inviting ground and wall reflections that need costly custom sensors. Keep the recommended minimum distance from the silo wall so the beam does not clip the wall at the measured level. Sizing rules: beam angle and minimum silo-wall distance.
RS485-model power cables may be extended on site; use thicker-gauge wiring to keep the operating voltage in the 9–12 V window and avoid drop-out at long runs. Never exceed the rated cable length without checking the voltage at the device. How-to: extending power supply cables.
The 4–20 mA output is mapped from the level reading, so set the installation height and the 4 mA / 20 mA endpoints first. Get either wrong and the current will read correctly at one point but drift everywhere else. Step-by-step: how to configure the 4–20 mA output values.
A wrong 4–20 mA reading is almost always calibration, wiring, or range-mapping — not a sensor fault. Recalibrate against the real receiver, check internal resistance and loop wiring, then re-check the endpoint map. Order-of-operations: solving an error in the 4–20 mA current output.
Multiple radars can share one RS485 bus, but each unit needs a unique communication address (factory default 127 / Modbus 0x7F). With unique addresses the upper computer can poll every unit. Bus topology and addressing: wiring RS485 radars in parallel.
No response from the upper computer usually means a wiring or voltage mismatch: for TTL use cross wiring (RX↔TX); for RS485 use straight wiring (A↔A, B↔B); and confirm the supply voltage matches the device. Diagnostic flow: no response via USB-to-serial adapter.
Our 80GHz units use FMCW (Frequency Modulated Continuous Wave) modulation at 76–81 GHz and speak Modbus and a plain text protocol. Knowing the exact protocol and register map saves hours when integrating with a PLC or SCADA. Reference: frequency, modulation scheme, and supported protocols.
Non-conductive targets such as a plastic disc reflect poorly. The field fix is to cover the disc surface with intact aluminium foil (no gaps or wrinkles) and add a waterproof film for long-term outdoor use to prevent oxidation and attenuation. Procedure: radar measurement on plastic disc targets.
Yes — set the installation height, and for 4–20 mA models calibrate the current endpoints. See the commissioning checklist above.
Yes, for RS485 models, using thicker gauge wire and verifying 9–12 V at the device at the full run length.
Almost always endpoint mapping or loop calibration, not the sensor. Re-check the 4 mA/20 mA points and the installation height.
Field-tested fixes for each topic above:
Installation height, perpendicular mounting and 4–20 mA calibration — the two settings to make before the first valid reading.
Why the ±2.75° beam cannot be narrowed, and the minimum distance to keep from the wall.
Thicker-gauge wiring that keeps 9–12 V at the device over long runs — RS485 models.
Set installation height plus the 4 mA / 20 mA endpoints first, or the current drifts everywhere.
Wrong readings are almost always calibration, wiring or range-mapping — the fix order that works.
Multiple radars share one bus with unique addresses (factory default 127 / Modbus 0x7F).
TTL cross wiring vs RS485 straight wiring, plus the supply-voltage checks that find the fault.
76–81 GHz FMCW modulation, Modbus and text protocol — the register map that saves PLC hours.
Aluminium-foil covering fix for non-conductive targets, plus the outdoor waterproofing step.
supply voltage matches the device specification; abnormal voltage prevents normal operation.
Check wiring:
TTL communication: Cross wiring rule – RX ↔ TX.
RS485 communication: Straight wiring rule – A to A, B to B.
Ensure no loose or misconnected terminals.
Test alternative baud rates (factory default: 9600; try 115200 or other common rates). Restore factory settings and retest if no reply is received.
Troubleshoot serial port hardware:
For TTL ports, run self-transmit/receive loopback test to validate serial transceiver functionality.
Swap serial adapters or host PCs for cross-verification to rule out faulty serial hardware.
Update the upper computer software to the latest version UartTool_20260103; older versions have compatibility bugs.
Measure operating current in series with a multimeter across the radar power terminals:
Zero current indicates hardware failure; return unit for repair.
Insufficient current means the power supply cannot drive the radar; upgrade power adapter to meet power requirements.
Answer: Set a unique communication address for each radar (factory default address: 127 / Modbus hex address 0x7F). Radars with unique addresses can be connected on the same RS485 bus, but the upper computer software can only poll one radar at a time.
Answer: Additional configuration is required: set the installation height; calibrate current for 4‑20 mA output models.
Installation height: Vertical distance from the water bottom to the radar hemisphere. After inputting this value, the system automatically calculates water depth via the current empty distance:
Water Depth = Installation Height – Empty Distance
Water depth: Vertical distance from the water bottom to the water surface. After inputting this value, the system automatically calculates installation height via the current empty distance:
Installation Height = Water Depth + Empty Distance
Only one of the two parameters above needs to be configured.
Precautions:
The set installation height cannot exceed the radar’s full measuring range.
Internal resistance varies between third-party display meters; perform an on-site current calibration matching the actual meter.
Configuration menus:
Installation height: Upper Computer – Installation Height / Bluetooth – Water Level Configuration – Installation Height
4‑20 mA current calibration: Bluetooth – 4‑20 mA Output Calibration – Current Calibration
Operation guide:
Cover the full disc surface with intact aluminum foil, no gaps or wrinkles.
Add a waterproof film for long-term outdoor use to prevent aluminum foil oxidation and signal attenuation.
For long-term open-air deployment or oversized targets: Use 0.1–0.3 mm thin aluminum sheets directly.
Answer: Operating frequency: 80 GHz; Modulation: FMCW (Frequency Modulated Continuous Wave); Supported protocols: Modbus, Text protocol.
Q: Can I extend the power cable myself? Can the cable be extended to 50 m or more?
A: Power cables for RS485 models may be extended on-site. Use thicker-gauge wiring to maintain operating voltage between 9‑12 V and avoid excessive voltage drop.
Answer: The 4‑20 mA output is mapped from the level reading, so the two things to set first are the installation height and the 4 mA / 20 mA endpoints.
It is the vertical distance from the water bottom to the radar hemisphere. The instrument then derives water depth automatically:
Water Depth = Installation Height – Empty Distance
Alternatively, input the current water depth and the instrument derives the installation height: Installation Height = Water Depth + Empty Distance. Only one of the two needs to be configured, and the installation height cannot exceed the radar’s full measuring range.
Map them to the level values you want at the bottom and top of the loop, for example 4 mA = empty tank and 20 mA = full tank.
Run Bluetooth – 4‑20 mA Output Calibration – Current Calibration with the actual receiving device connected. Installation height is at Upper Computer – Installation Height or Bluetooth – Water Level Configuration – Installation Height.
Note: internal resistance varies between third-party display meters and PLC analogue inputs, so always perform an on-site current calibration matched to the real receiver — otherwise the loop can read correctly at one end and drift at the other.
Answer: The beam angle cannot be reduced beyond its current specification — narrower angles increase interference from ground reflections and wall obstructions and require high-precision customized sensors with special calibration.
Wall clearance calculation formula:
H = R / tan(beam angle)
Where H = measuring height, R = minimum wall clearance distance
tan(2.75°) ≈ 0.04
Example: For a 7 m measuring height:
R = 7 × 0.04 = 0.28 m
A minimum wall clearance of 28 cm prevents radar beams from hitting silo walls.
Answer: A wrong 4‑20 mA reading is almost always a calibration, wiring or range-mapping issue rather than a sensor fault. Work through these in order:
If the output is still off after these checks, send us the loop current measurement, an installation photo and the echo spectrum; our support team will diagnose it with you.
Send us your tank count, distances and receiver type — we will map out the RS485 bus / 4–20 mA loops and the cable spec. Module JJY-YLD138M-32: MOQ 1 with free prototype.
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