Ultrasonic Open Channel Flow Meter

Ultrasonic Open Channel Flow Meter

I. Usage
Ultrasonic open channel flow meters are used in conjunction with weirs and flumes to measure the flow rate of water within open channels. Primarily employed for measuring the flow rates at wastewater discharge points of factories, institutions, and urban sewers. This instrument measures through the air using ultrasound, a non-contact method, thus offering higher reliability compared to other types of instruments in situations involving dirty, corrosive liquids.
II. Working Principle
The ultrasonic open channel flow meter directly measures the liquid level. When used for open channel flow measurement, a weir trough is installed on the open channel. The weir trough converts the size of the flow within the open channel into the height of the liquid level. The meter measures the water level in the weir trough and then calculates the flow rate by reversing the water level-flow relationship of the respective weir trough.
Common water measuring weirs include: triangular weirs, rectangular weirs, and Bache尔 trays.
When using an ultrasonic open channel flow meter, it is essential to know the water level-flow rate relationship of the weir trough being installed.
The water level-discharge relationship for the weir channel can be found in the National Metrological Verification Regulation "Open Channel Weir Flowmeter" JJG711-90.
The Bascule Slot knows the throat width b, and can calculate the water level-discharge relationship using the corresponding formula.
There are corresponding formulas for triangular and rectangular weirs as well. However, they also relate to the installed channel dimensions. When determining the water level-discharge relationship, the triangular weir is related to the channel width B, the opening angle, and the upstream weir crest height p.
The rectangular weir is related to the channel width B, the opening width b, and the upstream weir crest height p.
Ultrasonic Liquid Level Measurement Principle: This instrument employs the ultrasonic echo ranging method to measure liquid levels. The probe is fixed above the water weir trough level observation point. The probe is aimed at the water surface. The probe emits ultrasonic waves towards the water surface.
The working principle of the gauge: The gauge controls the probe to emit and receive ultrasonic waves, measures the transmission time of the sound waves to calculate the liquid level, and then converts the liquid level to flow rate (unit: liters/second) through the water level-flow rate table.
Ultrasonic Open Channel Flow Meter Display: The meter shows the liquid level height, instantaneous flow rate, and accumulates the instantaneous flow rate over time to determine the total flow rate.
Analog output available: 4-20mA current; Relay switch quantity (to be selected upon order); RS485 digital signals.
Section 3: Technical Specifications
Flow Range: 0.1 liter/second to 10 cubic meters/second (determined by the specifications of the water weir slot used)
2. Flow Uncertainty: 1-3%
3. Ultrasonic long-range measurement: 2 meters, 4 meters, 6 meters available
4. Blind Spot of Sensor: 0.4 meters (within 0.4 meters from the sensor's flange, not to be used for measurement)
5. Distance Measurement Error: ＜0.4% or ±3mm (within a 1-meter range)
6. Water Level Resolution: 1 millimeter
7. Instrument Protection: Probes are waterproof but not submersible; instruments are dustproof
8. AC or DC power supply: AC: 220V 50Hz 2W; DC: 12-24V.
9. Protection Grade: Display Instrument IP66, Probe IP68
10. Large Flow Rate: 4,290,000,000.00 cubic meters

IV. Selection of Weir Channels for Open Channel Flow Measurement

Choose the type of weir槽 based on the size of the flow within the channel, the flow pattern of the water within the channel, and whether a free flow can be formed. Depending on the flow rate, different weir槽 options can be selected.
① For large flow rates less than 40 liters/second, it is recommended to use a right-angled triangular weir.
② For flow rates greater than 40 liters/second, recommend using a Batcher box.

③ Shorter upstream channels, with flow rates greater than 40 liters/second, recommend using a rectangular weir.

V. Specifications of open channel flow meter weirs and actual installation photos on site:
Trapezoidal weir flow meter for open channel: (Materials: Optional of PVC, fiberglass, and stainless steel). Thicker walls correspond to higher flow rates.
1. Important Notes:
The dimensions at the triangular opening are accurate, the rim is straight and smooth. The surface of the board is smooth, flat, and free of warping.
The centerline of the triangular weir must align with the centerline of the channel.
The sill plate should be inserted into the channel wall, with the dimensions to be determined by the customer based on the on-site conditions.
The triangular weir is installed in the channel, ensuring the weir plate is vertical and centered on the channel's axis. During the machining of the triangular weir, the top angle may be rounded. When determining the water level at zero, be mindful that the water level zero point of the triangular weir should be at the intersection of the extensions of its side edges. The probe of the instrument should be installed 0.5 to 1 meter upstream from the weir plate, in a hygienic flow meter at the beverage factory.
Rectangular weir open channel flow meter: (Material options: PVC, glass fiber reinforced plastic, stainless steel) Wall thickness increases with the flow rate.
1. Important Notes
◇ The dimensions at the rectangular opening must be accurate, the edge platform should be straight and smooth. The board surface should be smooth, flat, and free of warping.
The centerline of the rectangular weir must align with the centerline of the channel.
The weir plate should be embedded into the channel wall, with dimensions to be determined by the customer based on the on-site conditions.
2. Application Range:
◇ Rectangular weir machining, note: The water-level-discharge relationship of a rectangular weir primarily depends on the weir opening width "b." It is also related to the upstream channel width "B" and weir sill height "p."
The rectangular weir is installed on the channel, ensuring the weir plate is vertical and centered on the channel's axis. The instrument's probe is positioned between 0.5 to 1 meter from the weir plate. Exquisite craftsmanship is evident.
Open Channel Flow Meter Baffled Flume: (Material options: PVC, Glass Reinforced Plastic, Stainless Steel) Thicker walls correspond to higher flow rates.
1. Important Notes:
The centerline of the Bascule slot must align with the channel's centerline to ensure the water flow into the Bascule slot is unobstructed.
◇ After the Bascule Channel is filled with water, the water flow should be free flow. The submergence of the Bascule Channel should be less than the specified critical submergence.
The upstream of the Bascule槽 should have a straight section wider than 5 times the channel width, allowing the water flow to enter the Bascule槽 smoothly. This ensures there is no lateral deflection of water, nor any thrust formed by the channel gradient.
◇ The Bascule channel must be securely installed in the channel. It should be tightly connected to the side walls and bottom of the channel to prevent any leakage. Ensure that all water flows through the measurement section of the Bascule channel. The measurement section of the Bascule channel is the throat section within the trough.
◆ Triangular weir installation

◆ Rectangular weir installation

◆ Barger groove installation

Section 6: Installation of Open Channel Flow Meters - Cautionary Notes for Waterway Weir Channels
The centerline of the water measuring weir should align with the channel centerline to ensure that water flows into the weir without deviation.
②. After the weir channel is in operation, the water flow should be free flowing.
Weirs: The downstream water level of triangular and rectangular weirs should be lower than the weir crest; the submergence of the Boucher's flume should be less than the critical submergence of the "Boucher's flume parameters."
③. The upstream section of the water measurement weir should have a straight section at least 5 times wider than the channel width, allowing the water to flow smoothly into the weir. The standard is "no splashes on the water surface." This means there should be no lateral flow and no force due to channel slope drop.
④. The water measuring weir槽 must be securely installed on the channel. Materials in contact with the channel medium: isolation diaphragm: 316L stainless steel, Hastelloy C-276, Inconel, or Tantalum (optional). The side walls and bottom connections must be tightly sealed to prevent leaks. Ensure that all water flows through the measuring section of the water measuring weir. The measuring section of the water measuring weir plate is at the weir opening; the measuring section of the water measuring channel is the throat section inside the channel.