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Industry Information
Use accuracy of vortex flowmeter
2012-2-10 15:41:28

Generally speaking, after excluding the quality problems of the flowmeter itself, most of them are problems of field installation. For common speed flowmeters, the possible situations are:

1. Is the straight pipe section in front of the flowmeter long enough (generally 10 times the inner diameter of the pipe), and must not contain elbows, bypass pipes or other impurities, flow blocking parts, etc.

2. Is the flowmeter installed upstream of the regulating valve?

3. Is there any vibration on site?

4. Is the flow rate too small to reach the lower limit of the flowmeter's measured value?

The following flowmeter manufacturers give a specific example of a vortex flowmeter:

在测焦炉煤气不稳定时,输出信号不稳定,原因有以下几点: When the coke oven gas is unstable, the output signal of the vortex flowmeter is unstable for the following reasons:

1. Vortex flowmeters are not suitable for installation in places with strong vibrations, which are widely known by users. However, in situations where the magnetic field changes frequently, the vortex flowmeter will measure a signal output higher than normal. Practice has proved that, in a scene where no gas flows,

When the sensor is in a changing magnetic field At the moment of the magnetic field change, the vortex flow sensor will sense an error signal and output it. When the change is over and the meter is in a stable magnetic field, the meter will output a normal signal.

2. Due to the high temperature and high humidity of the coke oven gas when it leaves the factory, there will be moisture in the gas transportation process. The gas flow drives the water back and forth to form a pulsating flow. When the vortex flow sensor is in this fluid state, the output data is large or small, and it can not be reversed at all.

映 Production status.

3. The crimping wire is not solid during the instrument wiring process, which causes the signal to be intermittent during transmission.

4. The ground wire of the instrument does not meet the requirements of the specification, so that 50Hz interference in strong electricity enters. When the normal signal is higher than 50Hz, a normal signal is output, otherwise an error signal is output.

5. Because the coke oven gas has many impurities, it is easy to crystallize, and the impurities are condensed on the sensor head, which causes measurement inaccuracy. When the temperature increases, the impurities evaporate, the sensitivity increases, and the signal increases; on the contrary, it decreases. As a result, data is unstable.

Vortex flowmeter for unstable measurement of coke oven gas:

1. During the installation and connection of the instrument, ensure that each link is accurate, including field inspections before installation, instrument wiring, and system grounding lines during installation, so as to ensure that real data is detected and can be accurately output. .

2. For the measurement system in operation, the method of “dual-track measurement, comparison and confirmation”, and the “replacement method” can be used to confirm and eliminate the measurement instrument failure in operation.

3. Regularly drain the pipeline, especially the water before the straight pipe section, and set a special person to discharge it regularly according to the specific conditions, reduce the water in the metering pipe section as much as possible, and eliminate the pulsation in the fluid to the maximum extent.

4. Strengthen the management of the measurement system data, set the timing printing function, and analyze the operation of the instrument based on the printed data combined with the production status.

5. Regularly clean the instrument as a whole. If necessary, purge the sensor head to avoid condensation of impurities at the sensor head. In the cold season, adding a heat tracing device to the metering straight pipe section and the meter part is also beneficial to alleviate the condensation of impurities at the metering meter.


是根据卡门(Karman)涡街原理测量气体蒸汽或液体的体积流量、标况的体积流量或质量流量的体积流量计。 LUGB type vortex flowmeter is a volume flowmeter that measures the volume flow, standard volume flow or mass flow of gas vapor or liquid according to the Karman principle. The screen can be used as a flow transmitter in automatic control systems.


The instrument adopts advanced differential technology and cooperates with isolation, shielding, filtering and other measures to overcome the problems of poor seismic resistance and small signal data disorder of similar products. The screen adopts unique sensor packaging technology and protective measures to ensure product reliability. . Product has base

This type and composite type, the basic type measures a single flow signal; the composite type can simultaneously measure temperature, pressure and flow. Each type has an integrated and split structure to suit different installation environments.


Features:


1. No moving parts, long-term stability, simple structure, easy to install and maintain


2. Using anti-disturbance circuit and anti-vibration sensor head, it has certain anti-vibration performance


3.Using ultra-low power single-chip microcomputer technology, one 3.2V 10AH lithium battery can be used for more than 5 years


4. Correct the instrument coefficient non-linearity by software to improve the measurement accuracy


5. Small pressure loss and wide measuring range


6. Use EEPROM to protect the accumulated flow from power failure, the protection time is more than 10 years

The main advantages of vortex flowmeters:


1) The structure of the vortex flowmeter is simple and firm, and it is easy to install and maintain.


2) There are many types of flow, such as liquid, gas, steam and some mixed-phase fluids.


3) Compared with differential pressure type and float type flowmeter, the accuracy is higher, which can generally reach plus or minus 1% R.


4) The range width is up to 10: 1 or 20: 1.


5) Small pressure loss, about 1/2 ~ 1/4 of orifice flowmeter.


6) Output a pulse signal proportional to the flow rate, suitable for total measurement, no zero point shift.


7) In a certain Reynolds number range, the output frequency signal is not affected by the fluid physical properties (density, viscosity) and composition. The meter coefficient is only related to the shape and size of the vortex generator and the pipeline. Suitable for various media

8) The corresponding eddy detection technology can be selected for different objects.


Limitations and accuracy of vortex flowmeters

Limitations of vortex flowmeters:

1) The vortex flowmeter is not suitable for low Reynolds number (ReD≤2 × 104) measurement, and its application is limited in the case of high viscosity, low flow rate and small diameter.


2) Vibration resistance detection instruments should be used in places where pipelines have vibration.

3) The stability of the vortex separation is affected by the distortion of the flow velocity distribution and the rotating flow. It should be configured with a long enough straight pipe section according to the different types of choke members on the upstream side. Generally, the straight pipe section of the throttling differential pressure flow meter can be installed.


相比,仪表系数较低,分辨率低,且口径越大越低,一般应用于中小口径(DN25~DN300)。 4) Compared with the vortex flowmeter , the meter coefficient is lower, the resolution is lower, and the larger the diameter is, the lower the diameter is. It is generally used for small and medium diameters (DN25 ~ DN300).


5) The application of the instrument in pulsating flow and mixed phase flow still lacks test data.