Aumeascon AM-D-DFM Digital Doppler Flow Sensor

AM-D-DFM  Digital Doppler Flow Sensor

1.Product Introduction

AM-D-DFM Digital Doppler Flow Sensor is with standard RS485 Modbus RTU,it measures the flow velocity according to the principle of ultrasonic Doppler effect, and can measure the water level and temperature through a pressure sensor and a temperature sensor. The shell is made of PVC plastic, which can effectively seal and water-proof. The shell is 25 cm long, 3 cm thick and 7 cm wide.Can measure the flow velocity in open channels and large pipes.

Technical Features

1)Using Modbus communication protocol and RS485 bus for communication.

2)Data acquisition host computer;one-to-many (a host computer mounts multiple slaves).

3)Simple product communication commands.

4)The underwater sensor with metal base fixing device is easy to install.

5)All equipment adopts electronic design, wide voltage power supply, low power consumption, and no mechanical parts. It has the advantages of accurate and stable measurement, high reliability and strong anti-interference.

6)Wide application. It can be applied in various water environments from tap water to river water with a lot of particles.

Working Principle

Doppler flow meter principle: When the ultrasonic sound source and the observer make relative motion, the frequency received by the observer will be different from the frequency of the ultrasonic sound source. Therefore, the small particles and small bubbles that move with the water relative to the ultrasonic transducer will also change the receiving frequency of the transducer, and increase with the increase of the suspended motion speed in the water, thus measuring the Doppler frequency shift, The velocity of the water at the point where the Doppler current meter is located is also measured.

Mainly used in irrigation open channels, municipal sewer, hydrological basins and other occasions. Especially suitable for occasions with low water level, it can work when the water level exceeds 15 cm. In regular pipelines and channels, the water depth is measured by the pressure sensor , and the flow velocity is measured by the ultrasonic sensor.it can easily calculate the flow rate.

2.Technical Parameters

Table 1 : Measuring index

Measuring Parameters Range Accuracy

Flow rate (m/s) 0.03~5.00 ±1.0% ±1cm/s

Water temperature(℃) -10~60 ±1(℃)

Water level(m) 0.05~10

(Factory default

maximum range 10m) 0.5%±0.5cm

Table 2: Performance Index

Item Range Remarks

working voltage(V) 7.2~15 DC

Current consumption(mA) <=85mA(Launch moment)

Quiescent current 6.5 mA 12V power supply

Data update cycle (s) 8 seconds Default

Size 25*7*3(Long*wide*thick)

Note: Factory default with 15m gas conducting cable.Special requirements please state in advance.

Table 3 : Wiring connection

Red Black Green Yellow Red(Hollow)

V12DC+ V12DC- RS485+ RS485+ Pressure

Note:The red and hollow wire is for pressure,not need to connection.

3.Transmission protocol

Modbus Protocol(Non-standard Modbus protocol)

The Doppler flow meter adopts the MODBUS protocol commonly used in industrial occasions to communicate with the upper computer. In the upper computer, the instantaneous flow velocity and cumulative flow are calculated according to the shape, flow velocity, and liquid level of the channel or pipeline. Easy to use, versatile and reliable.

Here we call the flow totalizer, RTU, and DTU the upper computer, and the flow meter as the lower computer or slave.

In order to be applied to occasions that are sensitive to power consumption, such as battery-powered occasions. The flow meter does not collect data before receiving the command from upper computer to read the data. At this time, the flow meter only has a static power consumption of 6.5mA/12V. After receiving the command to read the data from the host computer, start to collect data such as flow rate, which lasts at least 6 seconds, and the current is about 85mA/12V. Therefore, it takes at least 6 seconds for the host computer to receive the data returned by the flow meter after reading the integrated data. Obviously this does not comply with the standard Mudbus protocol.

Note:Any special requirements of communication protocol, negotiate with the manufacturer when ordering.

Precautions: The following data is in hexadecimal: sent and the response received is both in hexadecimal. Flow rate, temperature, and depth are all expressed in the form of data type IEEE754, and one data occupies four bytes.

Installation site requirements

The acoustic Doppler flow meter should be installed downstream of the straight section of the channel with a fixed cross-section. The longer the straight section, the higher the measurement accuracy, and there must be no overcurrent obstructions (such as sluices, weirs, etc.) within this distance to ensure the uniformity and stability of the water flow at the front of the sensor. The installation location should be as far away from the river bank as possible, placed horizontally from the center of the two banks, and placed vertically at the bottom of the water (provided that there is no silt in the watercourse, if there is, the location should be higher than the silt). As shown in Figure 1, when there are impurities deposited at the bottom of the canal and pebbles with growth or rolling of water weeds, the installation position can be raised to avoid the sediment at the bottom of the canal and the water weed covered probe or the collision of the probe with pebbles;The specific height of the acoustic Doppler flow meter from the bottom of the channel is preferably 5 cm, depending on the lowest measured flow level of the channel.When the channel has a high water depth and a certain minimum water level, it is sufficient to install the probe 0.5 times below the minimum water level for installation convenience.

Water depth requirement during measurement:

Calculated from the installation base plate of the acoustic Doppler flow meter, there must be at least 15 cm of water depth (Submerged the sensor), and the data measured below 15 cm of water depth will be biased. It is better to be larger than 20 cm.。

Figure 3 The installation of Doppler flowmeter

The function of the upper computer is to control the measurement interval of the Doppler flow meter by setting.Generally, in order to save power, the Doppler flow meter is often powered on during acquisition and a measurement command is issued, and powered off between measurement intervals.

The flow can be calculated through the measured water level and flow rate data, and can also directly mark and store the original flow rate and water level information with time stamp, or use SMS, GPRS and other means to transmit data remotely.

Air conducting pipe requirements

During installation, the air conducting cable should be led out of the water from the downstream direction of the flow meter along the bottom and wall of the canal. Best to use PVC pipes or stainless steel pipes to protect and fix along the way; If the probe is fixed with an arm bracket, the air conducting cable can be led out of  water along the hollow steel pipe of the support.

The Doppler flow meter comes with a 15-meter air conducting cable. In the middle of the cable, there is an air ducting used to balance the atmospheric pressure. The outer diameter of the air duct is about 2mm and the inner diameter is about 1mm. So be careful not to bend it. When the communication cable is drawn out of the water, it can be connected to the ordinary cable. At this time, the opening direction of the ventilation duct should be facing downwards and the ventilation tape should be used to protect it to prevent water and foreign objects from entering the ventilation tube.

Power supply requirements

 The 12V power supply used by the Doppler flow meter can come from batteries or solar energy, of course, it can also come from the city power. At present, there are two main types of power supplies that change from 220V AC to 12V. One is a linear power supply, which uses a power transformer; the other is a switching power supply, which is currently the most popular. When using the selection power supply, try to use a linear power supply. Because the brands of switching power supplies on the market are messy, some switching power supplies have large ripples, do not meet the relevant electromagnetic compatibility standards, and easily interfere with ultrasonic measurement.

6.Precautions

1)Since the air conducting cable contains the air ducting tube, it should not be bent excessively to prevent it from breaking; do not use the air conducting cable as the rope of the flow meter and use it to drag the Doppler flow meter;

2)The air ducting tube in the air conducting cable is connected to the circuit board inside the probe, and no water allow to enter. When installing, the end of the air ducting tube should be opened downward to prevent moisture from flowing into the probe circuit along the tube wall after condensation;

3)When the air-conducting cable is led out of the water , it should be protected by a PVC pipe as much as possible and fixed along the way or routed along the pipe of the bracket to avoid direct hydraulic impact and tensile force, Especially in the channels with a lot of Aquatic plants, when the cable line is hanging Aquatic plants, it will produce a lot of pulling force and may break the air-conducting cable line;

4)The round ultrasonic transducer in front of the probe cannot be impacted or scratched;

5)The wiring of the upper computer (Totalizer) and the probe must be connected correctly, otherwise the instrument will be damaged;;

6) The probe of the instrument should avoid prolonged exposure in the sun to avoid the temperature being too high and causing malfunction (the temperature of the probe should not exceed 60℃.);

7) The use of acoustic Doppler flow meter in places with high sediment concentration should regularly clean the sludge on the ultrasonic transducer and pressure sensor to prevent the sludge from blocking the pressure sensor.

8) Prevent the probe from being exposed to the sun in summer, and prevent freezing and cracking in winter. When not in use, it is best to remove the equipment and store it in the warehouse