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Differential Level Measurement in Bar Screening Channels

Enhancing Automation & Operational Efficiency at STP Inlet Screening

Product Installed

SBEM’s 136 ULT (Ultrasonic Level Transmitter)

Application Location

2.9 MLD STP

Industry

Sewage Treatment Plant (STP)

Background

In a Sewage Treatment Plant (STP), the bar screening system is the first and one of the most crucial stages of wastewater treatment. All incoming sewage passes through vertical or inclined metal bars that trap large solids, rags, plastic, and floating debris.

For continuous and smooth STP operations, the screening system must be cleaned at the right time. If the screen becomes clogged:

  • Water level rises before (upstream of) the bar screen
  • Flow reduces after the screen (downstream)
  • Risk of overflow increases
  • Mechanical stress is created on the screen
  • Treatment efficiency is affected

To manage this effectively, continuous differential level monitoring between the upstream and downstream channels is extremely important.

This differential measurement gives a clear indication of how much the screen is getting choked and when cleaning should be triggered.

Requirement

The customer required a monitoring system that could:

  • Measure level at the upstream channel (Before Screen)
  • Measure level at the downstream channel (After Screen)
  • Continuously calculate the level difference
  • Send this data to SCADA for automated cleaning logic
  • Provide reliable measurement in wet, corrosive, and wastewater environments
  • Reduce manual supervision
  • Ensure timely screening cleaning without overflow or delay

The need was to create a fully automated, safe, and maintenance-friendly screening process.

Product Installed

SBEM installed 136 ULT Ultrasonic Level Transmitters on both sides of the bar screen:

  • ULT–1 at the Upstream (Before Bar Screen)
  • ULT–2 at the Downstream (After Bar Screen)

Both readings were connected to SCADA, where differential logic was implemented.

How the Solution Works:

  • SCADA continuously compares upstream and downstream levels
  • When the differential percentage rises beyond the customer-set value, the system:
    • Automatically stops the flow process as required
    • Triggers the bar screen cleaning mechanism
    • Restarts the process once the level returns to normal

This approach ensures cleaning happens only when required, based on actual choking conditions.

Technology Used

  • Non-contact ultrasonic measurement ideal for wastewater
  • Continuous level monitoring with stable readings
  • Wide beam angle suitable for open channels
  • 4–20 mA / MODBUS / SCADA compatibility
  • Chemical and corrosion-resistant construction
  • Maintenance-free design (no contact with sewage)

Customer Benefits

  • Fully automatic bar screen cleaning based on true differential levels
  • Eliminates manual supervision and timing errors
  • Avoids overflow, choking, and emergency shutdowns
  • Reduces labour cost and enhances safety
  • SCADA-based monitoring ensures complete visibility
  • Allows customer to set their own differential threshold (%)
  • Increased life of mechanical equipment due to proper cleaning intervals
  • No contact with sewage: Longer sensor life and easier maintenance

Outcome

The 136 ULT-based differential measurement system provided the STP with a smart, automated, and dependable solution for bar screening management. With real-time level monitoring, SCADA integration, and automated cleaning logic, the plant now operates more smoothly, safely, and efficiently.

SBEM continues to serve as Your Measurement Partner, offering solutions that are Reliable Beyond Measure.