Characteristics and installation instructions of turbine flowmeter

1. Features of turbine flowmeter: From the previous discussion, we can see that turbine flowmeter is a flow meter with many advantages. In summary, it has the following features.

(1) High accuracy

The accuracy of the turbine flowmeter is about (0.5-0.1)%. Within the linear flow range, even if the flow changes, the cumulative flow accuracy will not decrease. And in a short period of time, the reproducibility of the turbine flowmeter can reach 0.05%.

(2) Wide range ratio

The range ratio of the turbine flowmeter can reach 8-10. Under the same caliber, the maximum flow value of the turbine flowmeter is greater than that of many other flowmeters.

(3) Strong adaptability

The turbine flowmeter can be made into a closed structure, and its speed signal is measured non-contact, so it is easy to achieve a high-pressure resistant design.

(4) Digital signal output

The output of the turbine flowmeter is a pulse digital signal proportional to the flow rate. It has the advantages of no reduction in accuracy during transmission, easy accumulation, and easy to be sent to the computer system.

2. Installation and use of turbine flowmeter products:

In order to give full play to the characteristics of the turbine flowmeter, full attention must be paid to the installation and use of the flowmeter. The following is a brief discussion of this issue.

(1) Test medium

The liquid measured by the turbine flowmeter is generally a low-viscosity (generally less than 15×10-6m2/s) and low-corrosive liquid. Although there are turbine flowmeters for measuring various media, the measurement of high-temperature, high-viscosity, and highly corrosive media still needs to be carefully considered and corresponding measures taken. When the medium viscosity v is greater than 15×10-6m2/s, the instrument coefficient of the flowmeter must be calibrated with real liquid, otherwise it will produce a large error.

Steam-liquid two-phase flow, gas-solid two-phase flow, and concentrated-solid two-phase flow cannot be measured using a turbine flowmeter.

(2) Installation piping requirements

The installation of the flow meter has a great influence on the measurement accuracy of the flow meter.

① Uneven velocity distribution and the presence of secondary flow in the pipe are important factors affecting the measurement accuracy of the turbine flowmeter. Therefore, the turbine flowmeter has certain requirements for the upstream and downstream straight pipe sections. For industrial measurement, it is generally required that the straight pipe length is 20D upstream and 5D downstream. In order to eliminate the secondary flow, it is best to install a rectifier at the upstream end. If the upstream end can ensure a straight pipe section of about 20D and install a rectifier, the measurement accuracy of the flowmeter can reach the accuracy level during calibration.

② Turbine flowmeters have high requirements for fluid cleanliness. A filter must be installed in front of the flowmeter to ensure fluid cleanliness. The filter can be funnel-shaped, and its cleanliness can be measured by the change in differential pressure at both ends.

③ To ensure that the liquid passing through the flow meter is single-phase, that is, air or steam cannot enter the flow meter, a degasser should be installed upstream of the flow meter if necessary. For liquids that are easily vaporized, a certain back pressure must be ensured downstream of the flow meter. The size of the back pressure can be twice the pressure drop of the flow sensor at the maximum flow rate plus 1.2 times the vapor pressure of the measured liquid at the highest temperature.

(3) Signal transmission line

In order to ensure that the display instrument has sufficient sensitivity to the pulse signal output by the turbine sensor, the signal-to-noise ratio must be improved. To this end, various electrical interference phenomena, namely electromagnetic induction, static electricity and capacitive coupling, should be prevented during installation. Therefore, when configuring the signal transmission line, the following points must be noted:

① Limit the maximum length of the signal line. The maximum length of the signal line is L = dV; where V is the effective value of the output voltage of the sensor coil at the minimum flow rate, mV; d is the coefficient, m/mV, and its value can be: when V < 1000mV, d = 1.0; when 1000mV < d < 5000mV, d = 1.5; when V > 5000mV, d = 2.0.

② Shielded cables should be used for signal transmission lines to prevent inductive noise from the outside. The transmission cable is required to be shielded and grounded at the display instrument end. The transmission cable cannot be close to strong electromagnetic equipment and is not allowed to be laid out with power lines.