Case Study: Non-Contact Water Level Measurement for Deep Manholes
A municipal utility required reliable, continuous water level monitoring in a deep manhole approximately 90 ft deep. The site had no access to power and contained internal structures such as grates, ladders, rungs, guide rails, inflow and outflow pipes, benching and wall irregularities. Steam, high condensation, and large temperature differences between the top of the manhole and the water channel at the bottom further complicated the measurement environment.
Measurement Challenges
Traditional manhole level measurement solutions typically use sensors mounted near the water surface or suspended on cables. These approaches can lead to unstable readings caused by wind induced movements inside the shaft. Sensors are also exposed to flooding, fouling and mechanical damage, resulting in frequent maintenance and high cost of ownership.
Intelligent Non-Contact Radar Level Sensor
To overcome these challenges, a remote battery-operated, non-contact radar level sensor from ABM was installed at the top of the manhole, which is safer and less expensive. These sensors use microwave radar technology with adaptive signal processing that automatically adjusts to changing conditions inside the manhole. False echoes from the grates and ladder are automatically filtered out and pushed under the noise level, allowing the sensor to lock onto water surface echo.
The radar sensor’s echo profile, shown in Figure 1, illustrates this capability, showing false reflections from the grates and rungs being rejected, while the true water surface echo is accurately detected.
Key advantages:
- Top-mounted installation: It is safer and simplifies installation and significantly reduces maintenance compared to bottom mounted or cable suspended sensors
- No cables or movement: Eliminates error caused by wind, flooding or mechanical wear
- Autonomous remote monitoring: Cellular communication and battery operated with solar recharging for long-term use at remote sites
- Low Cost of Ownership: Reduced installation effort and cost, minimal maintenance and no site visits
Conclusion
ABM’s wireless remote radar level sensor provides a reliable and cost effective solution for water level monitoring in deep manholes. By combining top mounted installation, intelligent echo processing software, and autonomous remote monitoring, the system delivers accurate measurements while eliminating the maintenance and reliability issues associated with traditional cable suspended and bottom mounted level sensor designs.