Installation: Marley LLC+u+bms Ultrasonic Water Level Control User Manual

Overview

The LLC+u+bms Ultrasonic Water Level Control is a sensor-only monitoring system for measuring water level in the cold-water basin of a cooling tower cell. It is intended for cooling-tower owners, controls contractors, and facility teams whose building management system (BMS) or programmable logic controller (PLC) will provide the display, alarms, makeup-water control, and other operating functions.

The system uses non-contact ultrasonic measurement inside a stilling chamber. It sends a continuous two-wire 4–20 mA signal to the BMS, allowing the control system to scale the signal into a water-level reading. The LLC+u+bms Ultrasonic Water Level Control does not include a standalone controller.

Specifications

• Measurement type: Non-contact ultrasonic water-level sensing
• Application: Cold-water basin of a cooling tower cell
• Sensor range: 49 inches (1.25 m); longer ranges are available
• Accuracy: 0.125 inch (3 mm)
• Resolution: 0.019 inch (0.5 mm)
• Dead band: 2 inches (50 mm)
• Beam width: 2 inches (50 mm)
• Power: 24 VDC loop power supplied by the BMS
• Power consumption: 0.5 W
• Maximum loop resistance: 400 ohms
• Signal: Two-wire 4–20 mA output
• Signal direction: 4–20 mA or inverted 20–4 mA
• Loop fail-safe choices: 4 mA, 20 mA, 21 mA, 22 mA, or hold last value
• Standard sensor lead: 30 feet (9.1 m), integrated into the sensor
• Sensor cable: Two-conductor, shielded, outdoor-rated cable
• Process temperature: 20° to 140°F (-7° to 60°C)
• Ambient temperature: -31° to 140°F (-35° to 60°C)
• Maximum working pressure: 30 psi (2 bar)
• Sensor process connection: 1-inch NPT or 1-inch G connection
• Sensor enclosure: Type 6P, encapsulated, corrosion-resistant, and submersible
• Sensor materials: Polycarbonate enclosure, Santoprene strain relief, and PVDF transducer
• Junction box: NEMA 4X (IP56) fiberglass enclosure with terminal strip
• Junction-box dimensions: 6 × 6 × 5 inches (15.2 × 15.2 × 13.7 cm)
• Assembly standards: UL 508A, CUL 508A, and NFPA 70 (NEC)

Detailed Description

The ultrasonic sensor measures the distance between its transducer and the water surface. Because the sensor does not contact the water, it avoids the direct immersion used by probe-style level controls. The BMS interprets the returned 4–20 mA signal as a continuous water-level value.

A stilling chamber is required. It calms turbulence in the basin and provides a stable mounting location above the water surface. Depending on the cooling-tower design, the chamber may be made from steel or PVC and may be installed inside the tower or externally.

The standard assembly includes the ultrasonic sensor, its integrated 30-foot outdoor-rated instrumentation cable, and a NEMA 4X fiberglass junction box with a terminal strip. The cable is factory connected to the sensor and terminates at the junction box.

The BMS supplies the 24 VDC loop power and receives the continuous level signal. The BMS is responsible for scaling, alarms, cutoffs, and control of the makeup-water solenoid or other connected equipment.

Available Assembly Configurations

• DL10 ultrasonic sensor with 30-foot cable only, without junction box or fittings
• DL10 sensor with 30-foot cable, junction box, and a 3-inch union slip fitting for an external round PVC stilling chamber
• DL10 sensor with 30-foot cable, junction box, and a 3-inch threaded fitting for an internal square metal stilling chamber
• Optional extension cable lengths: 100, 150, and 200 feet

Safety

Electrical shock and burn hazards are present during installation and service. Switch off power to the control panel before opening the junction box or working on connected equipment. If the disconnect is not within view, apply an approved lockout procedure.

• Only qualified personnel should install, maintain, or service the electrical equipment.
• Provide suitable branch-circuit sizing and protection for the control-panel supply.
• Verify that all electrical control circuits are properly grounded.
• Ensure safe access to the control panel and the customer-supplied disconnect.
• Follow applicable electrical codes and the safety instructions supplied with the cooling tower.
• Consider a formal safety review for the tower location, access routes, and field installation.

Setup and Operation

Install the Stilling Chamber

Fit the stilling chamber in a location that provides a calm measurement area and supports the ultrasonic sensor above the water surface. Confirm that the sensor has a clear acoustic path to the water and that the measured distance remains within the configured range.

Mount the Junction Box

Mount the fiberglass junction box near the cooling tower within the available sensor-lead length. The NEMA 4X/IP56 enclosure is suitable for outdoor installation when installed correctly.

• Route conduit into the bottom of the enclosure.
• Provide a drip line so water cannot run along the conduit into the box.
• Seal conduit interiors to limit vapor and condensation entry.
• Do not drill or rely on preformed knockouts; knockouts are not provided.
• Close and latch the cover so the gasket forms a watertight seal.

Connect the Sensor Loop

Connect the sensor conductors at the terminal strip and then connect the loop to the BMS 24 VDC supply and analog input. Use the terminal markings inside the supplied junction box.

• Red wire: 24 VDC power
• Black wire: Return
• Shield: Ground at the customer’s BMS panel only

The red and black conductors may be extended up to 1,000 feet (300 m) using 22-gauge or larger wire, subject to the loop-resistance limit and applicable local requirements. For extension wiring from the junction box, use 18-gauge, two-conductor, shielded stranded copper cable. Excess cable may be cut to length or coiled and secured.

Configure the BMS

The sensor is factory configured for a default distance of 4 feet 1 inch (1.25 m), with a standard operating range of 49 inches. The controls contractor normally scales the BMS to the actual distance from the bottom of the sensor to the basin floor, which is usually less than the factory range.

Set the BMS engineering range so the 4–20 mA signal corresponds to the real basin geometry. The BMS should then provide the water-level display and any required high-level, low-level, makeup, cutoff, or remote-alarm functions.

Typical installations do not require field programming of the sensor when the sensor-to-basin-floor distance is within the factory-configured range. Advanced configuration features include signal inversion and selectable loop-failure behavior, but these settings should match the requirements of the receiving BMS.

Operate the System

During operation, rising or falling water changes the ultrasonic distance measurement and therefore changes the 4–20 mA output proportionally. The BMS reads and scales this signal continuously. The LLC+u+bms Ultrasonic Water Level Control itself does not switch the makeup valve, stop a pump, or generate alarms; those functions belong to the connected BMS or PLC.

Troubleshooting

No Level Reading

• Verify that the BMS is supplying 24 VDC loop power.
• Check the red power and black return conductors at the junction-box terminal strip.
• Inspect the cable for damage, loose terminations, or excessive loop resistance.
• Confirm that the BMS analog input is configured for a two-wire 4–20 mA device.

Incorrect or Unstable Level

• Confirm that the sensor is centered and securely mounted above the stilling chamber.
• Check that the stilling chamber is present and calming the water surface.
• Verify that the BMS scaling uses the actual distance from the sensor to the basin floor.
• Ensure the measurement is outside the sensor’s 2-inch dead band.
• Check that the sensor beam is not obstructed and that the water surface is within the configured range.

Signal or Communication Fault

• Inspect the shield connection and ensure it is grounded only at the BMS panel.
• Check that the junction-box conduit enters from below and is sealed against moisture.
• Compare the BMS input value with the selected fail-safe setting: 4 mA, 20 mA, 21 mA, 22 mA, or hold last value.
• Confirm that the selected signal direction, 4–20 mA or 20–4 mA, matches the BMS configuration.

Sensor Replacement

The sensor lead is an integrated molded connection and is not designed to be detached from the sensor for separate replacement. Plan replacement around the complete sensor-and-lead assembly.

Maintenance

The ultrasonic sensor requires no routine maintenance. Periodically inspect the mounting arrangement, stilling chamber, junction box, conduit seals, cable jacket, and terminal connections as part of normal cooling-tower service.

• Keep the sensor face unobstructed.
• Check that the stilling chamber remains securely supported and free from conditions that could disturb the measurement.
• Confirm that the junction-box cover remains latched and its gasket seals properly.
• Retighten or repair field wiring only after isolating electrical power.

Pros & Cons

• Pros: Non-contact measurement, continuous 4–20 mA output, outdoor-rated sensor lead, corrosion-resistant sensor construction, and compatibility with customer BMS or PLC systems.
• Pros: The stilling chamber supports stable measurement in a turbulent cooling-tower basin.
• Cons: A stilling chamber and external BMS are required for a complete operating and control system.
• Cons: The standard sensor range is limited to 49 inches unless a longer-range configuration is used.
• Cons: Makeup control, alarm handling, cutoff logic, and level display must be provided and configured by the connected control system.