How the heat meter works

How the heat meter works: hot water (cold water) supplied by a heat source flows into the heat exchange system (radiator, heat exchanger or complex system composed of them) at a higher (low) temperature, flows out at a lower (high) temperature, in the process, releases or absorbs heat to the user through heat exchange (Note: This process includes the heating system and refrigeration system energy exchange process). As the water flows through the heat exchange system, the heat released or absorbed by the system is calculated and displayed by the calculator based on the flow rate given by the flow sensor and the temperature temperature given by the paired temperature sensor, as well as the time elapsed by the water flow. Q=∫qm×τ1τ0Δh×dτ=∫ρ×qv×Δh×dττ1τ0

Q ：系统释放或吸收的热量，J或kWh；

qm: mass flow rate of water flowing through the heat meter, kg/h;

qv: volumetric flow rate of water flowing through the heat meter, m3/h;

ρ: Density of water flowing through the calorimeter, kg/m3;

Δh: the enthalpy difference between the water at the inlet and outlet temperatures of the heat exchange system, J/kg;

τ: time, h.

Measurement principle of electromagnetic flowmeter

The working principle of the electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. When the conductive medium flows through the electromagnetic flowmeter, the induced electromotive force can be detected between the left and right electrodes on the wall of the flowmeter, and the magnitude of this induced electromotive force is directly proportional to the flow velocity of the conductive medium, the magnetic induction strength of the magnetic field, and the width of the conductor (the inner diameter of the flowmeter measuring tube), and then the flow rate of the medium can be obtained through calculation. The induced EMF equation is:

E=K×B×V×D

Where: E-induced EMF;

K-meter constant;

B-magnetic induction strength;

V-Measure the average flow velocity within the pipe section;

D - Measure the inner diameter of the tube.

When measuring the flow rate, the fluid flows through the magnetic field perpendicular to the flow direction, and the flow of the conductive fluid induces an induced potential proportional to the average flow velocity, so the conductivity of the measured flowing liquid is required to be higher than the minimum conductivity --- 5us/cm (the electromagnetic flowmeter can theoretically measure conductivity greater than 5μs/cm, but in the actual measurement, it should be ensured that the electromagnetic flowmeter should be used in the environment where the conductivity of the measured medium is 50μs/cm and above (greater than the theoretical value by one to two orders of magnitude). and must be based on the conductivity value measured online). The induced voltage signal is detected by two electrodes and transmitted to the converter via a cable, which is processed by a series of analog and digital signals to display the cumulative and instantaneous flow rates on the converter's display.

Electromagnetic flowmeter structure

As can be seen from the figure below, the electromagnetic flowmeter is mainly composed of the following parts:

1 - converter; 2-Flange; 3- Insulating lining;

4 - electrodes; 5 - measuring tube; 6-excitation coil;

7- Shell

The electromagnetic flowmeter is mainly composed of two parts: sensor and converter, of which the sensor includes flange, lining, motor, measuring tube, excitation coil, sensor housing and other parts; The converter includes parts such as the internal circuit board and the converter housing.

(1) Converter: provide a stable excitation current for the sensor, and at the same time amplify the induced EMF obtained through the sensor, convert it into a standard electrical signal or frequency signal, and display the real-time flow rate and parameters for the display, control and adjustment of the flow.

(2) Flange: used to connect with the process pipeline.

(3) Lining: a complete layer of electrical insulation corrosion-resistant material on the inside of the measuring tube and the sealing surface of the flange.

(4) Electrode: A pair of electrodes are installed on the wall of the measuring tube perpendicular to the magnetic field line, and the flow signal is detected, and the electrode material can be selected according to the corrosion performance of the measured medium. It is also equipped with 1-2 grounding electrodes for grounding and anti-interference in flow signal measurement.

(5) Measuring tube: the measuring tube flows through the measured medium. The measuring tube is welded from non-conductive stainless steel and flange, lined with an insulating lining.

(6) Excitation coil: A set of coils are installed on the outside of the measuring tube on the upper and lower sides to generate a working magnetic field.

(7) Shell: It not only protects the instrument but also plays a sealing role.