Sluice Gate Station Level Monitoring: Solar 4G Radar Level Transmitter Case Study
2026/10/27
The station controls a sluice gate on an irrigation and flood-control channel. Water level must be known upstream and downstream of the gate, with a 0–8 m measuring span, and the station is a remote site: a small brick cabin with no mains power, no fibre, and a mobile signal that varies from −75 dBm to −105 dBm depending on the season. In the flood season the channel carries silt and floating debris, and the level can rise by 2 m in a few hours.
| Field parameter | Typical value | Engineering consequence |
|---|---|---|
| Measuring span | 0–8 m, both sides of the gate | Long span and outdoor mounting; a single sensor per side is needed |
| Power | No mains; 12 V battery bank and 60 W solar | Average consumption must stay in the tens of milliamps |
| Network | 4G with variable signal | Data buffering and retransmission are required, not optional |
| Water surface | Silt, debris, ripple, occasional foam | Non-contact sensing avoids debris damage; float wells silt up |
| Environment | −20 to +50 °C, lightning-prone | Surge protection on power, signal and antenna |
- Staffed gauges were read twice a day, which is far too slow during a flood rise.
- A stilling well with a float sensor silted up within one season and then read a constant level, which is worse than no data.
- The previous telemetry unit lost its clock and timestamp after every power dip, so records could not be used for flood analysis.
- Lightning destroyed two transmitters in three years through the antenna cable.
The station needs a robust outdoor level measurement plus a self-powered data link that survives poor signal. The selected configuration is an 80 GHz radar level transmitter on a cantilever bracket over each side of the gate, connected to a solar-powered RTU with 4G and local SD-card logging.
| Selection item | Specified value | Reason |
|---|---|---|
| Principle | 80 GHz non-contact radar, ±3 mm | Narrow beam works over a channel with banks, piers and debris |
| Range | 0–15 m | Covers the 8 m span with headroom for flood peaks |
| Antenna | PTFE lens, IP67 | Handles silt splash and hose cleaning |
| Output | RS485 Modbus RTU | One cable to the RTU; both sensors can share the bus |
| Power | 12 V, 60 W solar, 100 Ah battery | Roughly 7 days of autonomy in cloudy weather |
| Telemetry | 4G router/RTU with 15-minute buffer and retransmission | Rides through short signal dropouts without losing records |
| Protection | DC surge arrester, antenna surge arrester, earth rod | Direct answer to the lightning history |
- Each radar is mounted on a galvanised cantilever arm fixed to the gate pier, with the antenna at least 1 m above the maximum flood level.
- The beam is aimed at a section of water 3–5 m from the bank where flow is representative, avoiding the gate lip where the surface is broken.
- The reference point is surveyed and entered as the datum, so the reported value is water level above a fixed local benchmark rather than distance to the sensor.
- Both sensors share one RS485 bus with different addresses; the cable screen is earthed at one end only to avoid a ground loop.
- The RTU is configured to store 30 days of 5-minute records locally, and to retransmit after a reconnect.
- Alarm thresholds are set in two stages: warning at 70 % of the warning level, urgent at 90 %, with SMS and platform alarms.
- Upstream and downstream levels now reach the management platform every 5 minutes, so gate operation during a flood rise is based on current data instead of a twice-daily reading.
- The radar does not contact the water, so silt and debris no longer block the measurement, and the stilling well was abandoned.
- With surge arresters and a separate earth electrode, no lightning damage has been recorded since the retrofit.
- Because records are buffered locally, short signal losses no longer leave gaps in the flood record.
Radar or ultrasonic for an open channel? Radar handles rain, wind and silt splash far better; ultrasonic is cheaper but its reading collapses in fog and heavy rain.
How much solar power is needed? Size for the worst week, not the best: a 60 W panel with a 100 Ah battery is a realistic starting point for a 5-minute reporting interval.
Can one RTU serve both sensors? Yes, on a shared Modbus bus with separate addresses — this halves the cost of the telemetry hardware.
- Survey and record the datum point; an unsurveyed reference makes all later data ambiguous.
- Confirm the mobile operator coverage at the site at the worst time of year, not by the coverage map.
- Include surge arresters and an earth electrode in the bill of materials — they are cheaper than a second transmitter.
