1Ultrasonic open channel flowmeterPrinciples for selecting installation locations
Requirements for water flow stability
Avoid interference sources: The installation location should be away from areas such as bends, gates, pump stations, etc. that are prone to eddy currents or surges, to ensure smooth water flow. For example, installing 50 meters downstream of the pump station can reduce the impact of water flow disturbance.
Straight section length: The length of the straight section upstream and downstream of the open channel must meet the requirements. It is recommended that the length of the straight section upstream be ≥ 5 times the width of the channel, and the length of the straight section downstream be ≥ 3 times the width of the channel to eliminate bias and impact.
Turbulence avoidance: Avoid installing in turbulent areas such as channel contraction or diffusion sections to prevent distortion of ultrasonic signals due to water flow fluctuations.
Environmental condition requirements
Electromagnetic interference isolation: The installation location should be far away from strong electromagnetic sources such as transformers and motors, with a recommended distance of ≥ 10 meters, or shielded cables should be used to reduce interference.
Temperature and humidity control: The ambient temperature should be between -20 ℃ and 60 ℃, and the humidity should be ≤ 85% to avoid sensor performance degradation caused by high temperatures or condensation caused by low temperatures.
Anti corrosion measures: In corrosive gas environments, IP67 protection level equipment should be selected, and the sensor surface should be regularly cleaned to prevent chemical substances from adhering.
Convenience of operation and maintenance
Space reservation: Sufficient operational space should be reserved at the installation location for sensor cleaning, calibration, and cable maintenance. For example, a channel of ≥ 0.8 meters must be reserved on both sides of the channel.
Protective facilities: When installed outdoors, the host should be placed in a sealed chassis to avoid exposure to sunlight and rain; Indoor installation should choose an area with good ventilation and no corrosive gases.
2、 Sensor installation specifications
Installation height and angle
Vertical alignment: The sensor emission surface should be perpendicular to the water surface, with a tilt angle of ≤ 5 °, otherwise it will cause signal reflection deviation.
Height adjustment: The distance between the bottom of the sensor and the highest water surface should be greater than 0.4 meters (blind zone range) to ensure that the measurement is not affected by water surface fluctuations. For example, in a channel with a depth of 1.5 meters, the sensor installation height can be set to 1.0 meter.
Bracket fixation: using concrete pouring bracket (grade ≥ C25), curing time ≥ 72 hours; Or use angle steel crossbeams to fix, ensuring that the horizontal error of the bracket is ≤ 0.1 °.
Sound channel and water flow direction
Multi channel layout: Time difference flowmeter requires the installation of transducers according to the manual requirements. Each pair of transducers should be on the same horizontal plane with an angle deviation of ≤ 1 ° to ensure flow measurement accuracy.
Mono optimization: Mono devices need to ensure that the channel is perpendicular to the direction of water flow, with a deviation angle of ≤ 3 °, to avoid signal attenuation.
Matching of measuring weir and channel
Weir selection: Choose the type of weir according to the flow rate: use a right angled triangular weir when the flow rate is less than 40L/s, use a Bacher weir when the flow rate is greater than 40L/s, and use a rectangular weir when the water level drop is large and the flow rate is greater than 40L/s.
Centerline alignment: The centerline of the measuring weir groove should coincide with the centerline of the channel, with a deviation of ≤ 5mm, to prevent measurement errors caused by water flow deviation.
Free flow conditions: The water level downstream of triangular and rectangular weirs should be lower than the weir crest; The submergence degree of the Bacher trough should be less than the critical value to ensure that the water flow is in a free flow state.
3、 Cable Connection and Wiring Specification
Cable type selection
Shielding requirements: Shielded cables (such as RVVP type) should be used to connect the sensor to the host, and the grounding resistance of the shielding layer should be ≤ 4 Ω to prevent electromagnetic interference.
Length limit: It is recommended that the length of a single cable be ≤ 100 meters. If it exceeds this limit, a signal amplifier should be installed to avoid signal attenuation.
Wiring path planning
Outdoor protection: The cable needs to be buried in galvanized steel pipes, with a burial depth of ≥ 20cm in the frost free soil area in the south. When crossing the river, it should be laid along the riverbed to avoid mechanical damage.
Indoor organization: The indoor part can be protected with PVC pipes, with a bending radius of ≥ 6 times the diameter of the cable to prevent cable breakage.
Wiring and use of cold press head
Secure connection: All wiring needs to be fixed with a cold press head, with matching wire diameter. After crimping, the tensile test should be ≥ 50N to prevent poor contact.
Waterproof treatment: Outdoor connectors need to be wrapped with waterproof tape and coated with silicone sealing, with a protection level of IP65.
4Ultrasonic open channel flowmeterDebugging and Calibration Standards
Parameter Settings
Weir slot parameter input: Set the weir slot type, size (such as Bacher slot throat width), material and other parameters in the host, with an error of ≤ 1%.
Sound speed correction: Adjust the sound speed value based on the temperature of the medium (such as water sound speed of 1483m/s at 20 ℃), and correct the sound speed by about 3m/s for every 10 ℃ temperature change.
Signal testing
Troubleshooting for loss of test: If a certain transducer cannot stably measure speed, adjust the angle (≤ 1 ° each time) or check the cable connection until the signal strength is ≥ 80%.
Installation of waveguide: When the water surface fluctuates violently, a waveguide (with a diameter of 100mm and a length exceeding the edge of the weir) can be installed at the front end of the sensor, and the front end can be cut at a 45 ° angle to reduce wave interference.
Comparison and verification
Multi water level test: Measure three times each under high, medium, and low water level conditions, and compare the results with those obtained by the navigation ADCP or current meter method. The error should be ≤ ± 5%.
Parameter optimization: If the error exceeds the standard, the flow coefficient or zero offset in the host needs to be adjusted until the accuracy requirements are met.