The turbine flowmeter features and installation
Published on：2014-12-15 9:49:07 Hits：
1. Features turbine flowmeter
Seen from the foregoing discussion, the turbine meter is a flow meter has many advantages. To sum up, it has the following characteristics.
(1) high accuracy
Turbine flowmeter accuracy in (0.5-0. 1) about%. The linear flow range, even if the flow rate changes, the cumulative flow accuracy is not reduced. And in a short time, the reproducibility of the turbine flowmeter up to 0.05%.
(2) the range than the width
Turbine flowmeter turndown ratio up to 8-10. In the same caliber, the maximum flow rate value is greater than many other turbine flowmeter flowmeter.
Turbine flow meter can be made into a closed structure, the speed signal is non-contact measurement, it is easy to achieve high voltage designs.
If the turbine flowmeter selection and bearing temperature, thermal expansion coefficient of the material, it can be used in a wide temperature range. At this point, it should be noted that the meter factor correction (mainly changes in their circulation section):
K = K 0 [1- (R +2 H) (t-to)] (3-23)
Where K, K 0 - when to use and when the meter calibration coefficient;
t, t 0 - when to use and when the fluid temperature calibration;
R, H, respectively, and the material expansion coefficient of the turbine casing.
(4) digital signal output
Turbine flowmeter output is proportional to the pulse and flow of digital signals. It has not reduce accuracy in the transmission process, is easy to accumulate, easy into the computer system advantages.
2. The turbine flowmeter installation
To give full play to turbine flowmeter features using a flowmeter is installed on must also be fully Note SUMMARY The following discussion about this problem.
(1) measured media
Turbine flow meter measured liquid, usually (in general should be less than 15 × l0 -6 m 2 / s), low corrosive liquids of low viscosity. Although there have been a variety of media for the turbine flowmeter to measure, but the high temperature, high viscosity, highly corrosive media measurement still need careful consideration and take appropriate measures. When the medium viscosity v is greater than 15 × l0 -6 m 2 / s, the instrument must be a real factor liquid flowmeter calibration, otherwise it will cause large errors.
Vapor - liquid two-phase, gas - solid two, thick - solid two phase flow turbine flow meter can not be measured.
(2) install piping requirements
Flowmeter installation a great influence on the measurement accuracy of the flowmeter.
① uneven velocity distribution of the inner tube and the presence of secondary flow is an important factor in turbine flowmeter measurement accuracy impact. Therefore, the turbine flowmeter for upstream and downstream straight pipe - fixed requirements. For industrial measurement, generally require straight pipe length upstream 20D, downstream 5D's. To eliminate the secondary flow, the best installation at the upstream end rectifier. If the upstream end of the straight sections to ensure that there are about 20D, and to install a rectifier, flowmeter measurement accuracy can reach the level of accuracy of the calibration time.
② turbine flowmeter fluid cleanliness have higher requirements, the meter must be installed before the filter to ensure clean fluid. Filters may be funnel-shaped, its own cleanliness, changes in differential pressure can be measured at both ends obtained.
③ is ensured by a single-phase liquid flow meter, that can not let air or steam into the flow, upstream of the flowmeter installed if necessary eliminator. For easy vaporized liquid, downstream of the meter must be guaranteed in certain backpressure. Twice the size of the back pressure of the desirability plus 1.2 times the maximum temperature measured vapor pressure of the liquid flow sensor voltage drop at maximum flow.
(3) the signal transmission line
In order to ensure indicator of the pulse signal output from the turbine sensors have sufficient sensitivity, it is necessary to improve the signal to noise ratio. For this reason, the installation should prevent all kinds of electrical interference phenomena, namely electromagnetic induction, electrostatic and capacitive coupling. Therefore, when configuring the signal transmission line, must pay attention to the following points:
① limit the maximum length of the signal line. The maximum length of the signal line is, L = dV; wherein, V is the effective value of the output voltage of the sensing coil at the minimum flow rate, mV; d are coefficients, m / mV, its value can be: V
② signal transmission lines should be shielded to prevent induction noise from the outside. Require transmission cable shield grounding terminal display instruments. Transmission cable is not near strong electromagnetic devices, do not allow the power line almost arranged in a row.
(4) operation and maintenance
① When the pipe turbine flowmeter needs cleaning, you must open the bypass, the cleaning liquid can not flow meter.
② piping system must be open when you start bypass to prevent a sudden increase in the flow rate, causing excessive damage to the turbine speed.
③ turbine flowmeter bearings should be changed regularly, and can be used to observe its bearing wear under low flow characteristics change.
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