Trumsense Ultrasonic Open Channel Flowmeter 4-20ma Output Parshall Flume Open Channel Measure Flow Velocity Instantaneous Flow Rate Cumulative Flow Amount Water Depth And Temperature

Item No.: 00254
The meter measures the water level in weirs or flumes first and calculates the flow rate according to the relationship between water level of the measuring weir and flume and the flow rate.
Description Review



1. Principle of Ultrasonic Liquid-level Measurement

The water flow in the open channel can be measured through the match use of ultrasonic open channel flowmeter and the measuring weirs and flumes. It is mainly used for the flow of the measuring sewage discharge outlets of sewage plants, enterprises and institutions, the flow of urban sewage and irrigation channels.


This series of meters are to directly measure the liquid height in a channel or flume. When it is used to measure the flow of open channel, the measuring weir and flume shall be installed on the open channel. The measuring weir or flume changes the flow rate in the open channel to the level of liquid. The meter measures the water level in weirs or flumes first and calculates the flow rate according to the relationship between water level of the measuring weir and flume and the flow rate.


The ultrasonic pulse emitted by the transmitting ultrasonic transducer is transmitted to the measured surface through air. After that, it is returned to the receiving transducer by air after reflection. Then, the time of ultrasonic pulse transmitted and received in sound transmission media is measured. Based on the speed of sound in the air, the distance from the transducer to the liquid level can be calculated. The liquid level is therefore determined. So, we can calculate the distance from the probe to the reflective surface D = C * t/2 (divided by 2 because the sound wave is a round-way from transmitting to receiving. D indicates the distance, C indicates the speed of sound, t indicates the time). Then, the liquid level can be calculated by subtraction.



2. Principle of Water Flow Measurement in Measuring Weirs and Flumes

The larger the flow in the open channel with smooth circulation, the higher the liquid level. The smaller the flow, the lower the liquid level (as shown in Fig. 2.1). The flow can be calculated by measuring the water level. The corresponding relationship between flow and water level in ordinary open channels is affected by slope ratio and surface roughness. The measuring weirs and flumes in the channel can be installed for throttling, so that the flow rate and liquid level in the open channel have a fixed corresponding relationship, which mainly depends on the size of measuring weirs and flumes, and  minimize the influence of the channel as far as possible.


   Right triangle weir, rectangular weir and Parshall flume are commonly used.


If to use the ultrasonic open channel flowmeter, it is necessary to know the relationship between the water level of the measuring weir or flume and the flow before the installation.

The relationship between the water level of the measuring weir or flume and the flow can be found out in the national metrology verification regulation, Verification Regulation of Weirs and Flumes for Flow Measurement (JJG711-90),  a part of which is excerpted for this manual. After the throat width of the Parshall flume is known as b, the corresponding relationship between water level-flow can be calculated by the corresponding formula.

The relationship for that of the right triangle weir can also be calculated with this formula.

Rectangular weir also has a corresponding formula, and it's also related to the size of the channel being installed. During the determination of water-flow relationship, the width B, opening width B and upstream weir ridge height p shall be considered.


If you are not familiar with the calculation of the water level of the weir/flume and the flow, you can inform the meter manufacturer of the parameters of the measuring weirs and flumes. The manufacturer shall help the calculation. It shall be noted that the above parameters related to the determination of the water-flow relationship shall also be provided.




3. Basic technical parameter:



Split type

Probe selection

Sensor selection:

It is suggested to adopt 100KHz M48×2 probe for No. 1-4 Parshall flume. The measuring range is 1m, so that it is not likely to hit the wall of the Parshall flume or corners to form a false signal.

The M48×2 probe has a small blind area, only 10 cm, and the mounting bracket can be made even lower.

It is suggested to adopt 64Khz M48×2 probe for No. 5-25 Parshall flume. The measuring range is 2m, and the blind area is 30cm.

Measuring range

Parameters ranging from 0.1L/s ~ 99999.99m /h can be determined according to different weirs and flumes.

Accumulative flow

Max.: 4290000000.00m3

Maximum range of liquid level

It can be made for three types, 1m, 2m and 3m. If large range is required, it shall be customized.

Liquid level measurement accuracy



3mm or 0.1% (whichever is greater)


Chinese LCD display

Flow measurement accuracy

1~5% is for standard weirs and flumes (those meet the requirements of the national standards.)

10~50% if for non-standard weirs and flumes.

Analog output

4-wire 4~20 mA/600Ω load

Relay output

(Option) 2 groups of AC 220V/ 8A or DC 24V/ 5A,

Power supply

220V AC+15%  50Hz, or 24VDC 120mA;

Power supply

(Option) 12VDC, battery power supply, solar power supply

Working environmental temperature

Display meter -20~+60℃, probe -20~+80℃

Working environment pressure

Normal atmosphere

Working environmental humidity

≤90%RH, non-condensation

Process temperature


Process pressure

Normal atmosphere


Optional 485 and 232 communication, MODBUS protocol

Protection class

Display meter IP65, probe IP68

Display meter IP64, probe IP68

Probe cable


Standard 10m, 100m at maximum

Probe material

The standard material is ABS, and anti-corrosive material shall be used in corrosive environment.



product power consumption

The split-type meter is powered by 24V power supply, and the power consumption without relay is 100mA. It needs 120mA if with one relay, 145m if with two relays, 170mA if with three relays and 190mA if with four relays.

Specific power is as follows:

24×100mA= 2.4w for no relay;

24×120mA=2.9W for 1-way relay; 24×145mA=3.5W for 2-way relay;

24×170mA=4.1W for 3-way relay; and 24×190mA=4.6W for 2-way relay;


product power consumption

The integral four-wire system is powered by 24V power supply, and the power consumption without relay is 80mA. It needs 105mA if with one relay, and it needs 130m if with two relay.

24×145mA=3.1W is for 2-way relay



4. Shape and Size of Open Channel Flowmeter:


The meter display of the split-type ultrasonic open channel flowmeter should be installed indoors. The room should be well ventilated and free from corrosive gases. The meter shall be mounted on the wall. If the indoor conditions are not good or it shall be hung in the outdoor, it shall be installed in the meter protection box to avoid the sun exposure and rain.


5. Ultraosnic Probe  Installation:

The probe of ultrasonic open channel flowmeter can be installed directly above the observation point of water level of the measuring weir and flume. The probe transmitting surface shall align and perpendicular to the water surface. A level can be placed on the top cover of the probe and the probe shall be leveled to align the water surface. The water level observation point of Parshall flume shall be 0.1 ~ 0.5 m from the upstream of the flume; and that of triangular weir and rectangular weir shall be on one side of the upstream, which is  3 ~ 4 times of the maximum water depth through the weir away from the weir plate.


6. Bottom Thread Installation:


7. Top thread mounting - Hoisting installation:


8. Stilling Well Installation:

In many cases, there are measurement errors or no measurement signal because the water in the channel may have garbage, foam or other floating objects; or because there are no straight channels of sufficient length upstream and the water surface fluctuates greatly. In that case, stilling well can be used.

The inner wall of the stilling well shall be > 50cm in diameter, and the inner wall shall be smooth without any bumps and burrs. After the probe is installedthe transmitting surface of the probe shall be >0.3m away from the highest water surface.

9. Installation of triangular weir




10. Installation of rectangular weir





11. Installation of Parshall flume




12. Installation of Weirs and Flumes

 The center line of the measuring weir and flume shall be aligned with the center line of the channel to make the water flowing into the weir and flume without bias current.

After water flows through the measuring weir and flume, the water shall have free flow.

The downstream water level of triangular weir and rectangular weir is lower than the weir ridge. The submergence degree of the Parshall flume is less than the critical submergence degree in the "Parshall flume parameters".

There shall be flat and straight section greater than 10 times the width of the channel in the upstream of the measuring weir and flume at minimum, so that the water flow can enter the measuring weir and flume smoothly, for which there shall be "no spray on the water surface". That is, there shall be no left and right drift, nor the channel slope formed by the thrust.

If the upstream of the measuring weir and flume is less than 10 times of the flat and straight section, and the water flow fluctuates greatly or there is a large amount of foam, two layers of dampers with holes can be added, as shown in the figure below.


The measuring weir and flume shall be fixed on the channel. It should be closely connected with the side wall and the bottom of the channel without water leakage. The water flow shall flow through the measuring part of the weir and flume. The measuring part of water measuring weir plate is the weir crest, and the that of the measuring flume is the throat section in the flume.




13. The reasons why you choose trumsense to purchase?

● OEM ODM factory

● 7x24 hours online proposal supplied

● 100% satisfied after-sales services

Trumsense Technology is an ultrasound technology company integrating R&D, production and sales. Focusing on the R&D and production of ultrasonic material (liquid) level meters, liquid level difference meters, open channel flow meters, mud level meters, sensors, transducers and other products, it occupies nearly 45% of the ultrasonic liquid level and material level industry market.


Mainly engaged in ultrasonic material (liquid) level meter series, pressure level / transmitter series, flowmeter series.


The main application fields of the product: sewage plant water works, mines, water conservancy, power plants, chemical plants, steel plants, printing machinery manufacturing plants, etc., liquid level measurement in various industrial fields, especially sewage treatment, acid and alkaline liquid measurement.





14. Application Examples:

This series of meters directly measure the liquid level of channels or flumes. The measuring weir flume shall be installed for the measurement of open channel. The measuring weir flume is able to transfer the flow in open channel to the liquid level. The instrument will work out the flow based on the water level in the measuring weir flume and according to the relationship between the water level of measuring weir and the flow.



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