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Working Principle of Water Flow Sensor

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Water flow sensor is a lower configuration of turbine flow meter, similar structure and principle, but water flow sensor adopt cheap accessory, price will be very low; and the flow sensor could measure small water flow, this advantage is better than turbine flow meter. sometimes, some user use the water flow sensor to replace the flow meter.

brass water flow sensor

GE-302H Brass Water Flow Sensor

1/2" Male + Female connection, produced by Brass material, stability a...


1. Working principle

The water flow sensor is mainly composed of copper valve body with water flow rotor assembly, steady flow assembly and Hall element . It is installed at the water inlet end of the water heater to measure the water inlet flow. When water flows through the rotor assembly, the magnetic rotor rotates and the speed changes linearly with the flow rate. The hall element outputs the corresponding pulse signal to the PLC controller. The controller calculate the water flow rate and regulates the current of the proportional valve, so as to control the gas volume through the proportional valve, so as to avoid the phenomenon of heating in summer and cooling in winter during the use of the gas water heater. The water flow sensor fundamentally solves the problems of high starting water pressure of differential pressure water air linkage valve and dry burning of flap water valve. It has many advantages, such as sensitive reflection, long service life, quick action, safety and reliability, convenient connection and ultra-low starting flow (1.5L / min), etc. it is deeply loved by users.





The water flow rotor assembly is mainly composed of turbine switch housing, magnetic rotor and brake ring. When the water flow switch is used, its performance is better than that of the mechanical differential pressure plate structure, and its size is obviously reduced. When the water flows through the turbine switch housing, the magnetic rotor is driven to rotate. When different magnetic poles are close to the hall element, the hall element is on, and when they leave, the hall element is disconnected. Thus, the rotor speed can be measured. According to the measured water flow, rotor speed and output signal (voltage) curve, the starting water pressure of the water heater can be determined, and the starting water flow corresponding to the starting water pressure and the starting speed of the rotor can be determined. 

water flow sensor 3/4"

GE-302D Brass Liquid Flow Sensor

BSP1/2" BSP3/4" Male Thread Water Flow Sensor, produced by Brass mate...

By the control circuit, the water heater can start when the rotor speed is greater than the starting speed, and stop when the rotor speed is less than the starting speed. In this way, the starting water pressure of the water heater is generally set at 0.01 MPa, and the starting water flow is 3-5 L / min (it needs to meet the limit of * temperature rise in the water heater standard). In addition, the water becomes magnetized water under the magnetic field cutting of permanent magnet material, and the oxygen content in the water increases, which makes people feel fresh after bathing. The function of the brake ring is to stop the rotation of the high-speed rotating magnetic rotor and terminate the pulse signal output when the water is stopped. If the controller cannot receive the pulse signal, it shall immediately control the gas proportional valve to close the valve, cut off the air source and prevent dry burning.

PDA potable water flow sensor

BSP1/4“ Potable Water Flow Sensor

achieving the FDA standard, widely used in RO water instrument, dispen...


2. Basic principles

Water flow sensor uses Hall effect of Hall element to measure magnetic physical quantity. At the same time, 5V DC voltage is applied and the current direction is orthogonal to the magnetic field direction. When the water pushes the magnetic rotor to rotate through the turbine switch housing, the rotating magnetic field of different poles is generated, the magnetic induction line is cut, and the high and low pulse levels are generated. Because the output pulse signal frequency of Hall element is proportional to the rotating speed of magnetic rotor, and the rotating speed of rotor is proportional to the water flow, start the gas water heater according to the water flow. The empirical formula of its pulse signal frequency is shown in formula .


F=8.1Q-3
 F-pulse signal frequency, H2
Q - water flow, L / min

The feedback signal of water flow sensor is used to judge the value of water flow through the controller. According to the different types of gas water heater, the startup flow of * can be selected to realize the ultra-low pressure (below 0.02MPa) startup.

3. Comparison between water flow sensor and water air linkage valve

The disadvantage of the differential pressure type water air linkage valve is that the starting water pressure is high, and in order to reduce the starting water pressure, it needs to sacrifice certain steady flow characteristics (flow stability ability when the water pressure fluctuates).

plastic body water flow sensor

Plastic Water Flow Sensor

BSP1/2" BSP3/4" BSP1" DN32 DN40 DN50 plastic water flow sensor, both e

In order to give consideration to both, only increase the diaphragm of water valve, but the cost will increase with the increase of valve body, and the start-up pressure index of water flow cannot be too low. For the water flow sensor, a steady flow component is added at the outlet end to make use of the steady flow. Through the test, the steady flow components for different capacity water heaters have been successfully developed, which have good steady flow characteristics (when the water inlet pressure changes from 0.1 to 0.5MPa, the water output changes within 3L / min). When the water inlet pressure changes, the flow is kept within a certain range to achieve constant temperature effect.
Comparing the pressure difference type water air linkage valve with the water flow sensor, we can see that the former is mechanical type, with complex structure and large volume, but the control circuit is simple; the latter is electrical type, with relatively simple structure and small volume, but the control circuit is complex. More importantly, the former has high starting water pressure and high resistance of water system, so it is not suitable to be used in large capacity water heater AZ above 10L / min; the latter has low starting water pressure and low resistance of water system, which has been widely used in large capacity water heaters above 10L / min.

4, conclusion
In recent years, the use of water flow sensor to measure flow has been widely used in the digital constant temperature gas water heater. It has been proved that the use of water flow sensor has the characteristics of simple structure, high reliability and wide measurement range. If it can be adjusted with the gas volume proportion of the gas proportional valve, the full automatic control of the gas water heater in the combustion process can be realized

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