2019-10-18 08:18:45

Plug-in ultrasonic flowmeter features

Programmable frequency low frequency rectangular wave excitation improves stability of flow measurement and low power loss;

Using 16-bit embedded microprocessor, the operation speed is fast and the precision is high;

Full digital processing, strong anti-interference ability, reliable measurement, high precision, flow measurement range up to 100:1;

Ultra-low EMI switching power supply, suitable for wide range of power supply voltage and good anti-EMC performance;

Full Chinese character menu operation, easy to use, easy to operate, easy to learn and understand;

High definition backlit LCD display;

It has two-way flow measurement and two-way total accumulation function, and the current and frequency have bidirectional output function;

There are three totalizers in the internal to display the forward cumulative amount, the reverse cumulative amount and the difference integrated amount;

With RS485 or RS232 digital communication signal output

It has a conductivity measurement function to determine whether the sensor is empty or not;

The constant current excitation current range is large, and can be used with different companies and different types of electromagnetic flow sensors;

With self-test and self-diagnosis function;

High reliability with SMD devices and surface mount (SMT) technology;

The internal design of the meter has a power-down clock that can record 16 power-down times.

Several problems of steam metering and their solutions

Steam is one of the important energy sources for enterprise production. It is the main heat energy for urban central heating and an important indicator for economic accounting. Therefore, the accuracy of steam metering is particularly important.

In order to solve the problem of heating for employees, the company has updated the original boiler equipment, adding 4 new boilers (2 sets of 25t/h, and another 2 sets of 35t/h). The DCS realizes the automatic control of the boiler system, and the product is saturated steam.

Analysis of problems and influencing factors

Starting from the boiler ignition operation in November 2010, the steam flow often shows the maximum value, and the differential pressure signal measured by the differential pressure transmitter exceeds 20 mA. The same is true when the load is low and the actual flow is small. In this case, steam flow measurement does not provide a safety reference for boiler operation, and it cannot be used for cost accounting.

In response to this phenomenon, the design of the project uses a V-cone flowmeter, equipped with an intelligent differential pressure transmitter, and the measurement signal is sent to the DCS for calculation and display.

Ultrasonic flowmeter measurement principle

When the ultrasonic beam propagates in the liquid, the flow of the liquid will cause a small change in the propagation time, and the change in the propagation time is proportional to the flow velocity of the liquid, and its relationship conforms to the following expression.

among them

θ is the angle between the sound beam and the direction of flow of the liquid

M is the number of linear travels of the sound beam in the liquid

D is the inner diameter of the pipe

Tup is the propagation time of the sound beam in the positive direction

Tdown is the propagation time of the sound beam in the reverse direction

ΔT=Tup –Tdown

Let the speed of sound in the stationary fluid be c, the velocity of the fluid flow be u, and the propagation distance be L. When the sound wave is in the same direction as the fluid flow direction (ie, the downstream direction), the propagation velocity is c+u; otherwise, the propagation velocity is cu. Two sets of ultrasonic generators and receivers (T1, R1) and (T2, R2) are placed at two places separated by L. When T1 is in the forward direction and T2 transmits ultrasonic waves in the reverse direction, the time required for the ultrasonic waves to reach the receivers R1 and R2 respectively is t1 and t2, then

T1=L/(c+u); t2=L/(c-u)

Since the flow velocity of the fluid in the industrial pipeline is much smaller than the sound velocity, that is, c>>u, the time difference between the two is ▽t=t2-t1=2Lu/cc. Thus, the propagation velocity of the acoustic wave in the fluid is known. When it is known, the flow rate u can be obtained by measuring the time difference ▽t, and the flow rate Q can be obtained. The method of measuring the flow using this principle is called the time difference method. In addition, a phase difference method, a frequency difference method, or the like can be used.