Turbine flow meters are very important for our daily work and production. There are many ways to ensure the accuracy of turbine flow meter measurements. Turbine flow meter to improve the accuracy of the measurement of three major methods: selecting the viscosity of the liquid medium, meeting the requirements related to the straight pipe section before and after the instrument, and adopting anti-interference cable.
Method 1: Selecting the Viscosity of the Liquid Medium
Turbine flow meter measured by the liquid, generally low viscosity (generally should be less than 15 × l0-6m2/s), low corrosive liquid. Although they are already used for a variety of media measurement turbine flow meters, the high temperature, high viscosity, and strong corrosive media measurement still need to be carefully considered. When the medium viscosity is greater than 15 × l0-6m2/s, the flow meter instrumentation coefficient must be calibrated for the real liquid, otherwise, it will produce a large error.
Method 2: Meeting the Requirements Related to the Straight Pipe Section Before and After the Instrument
- Uneven flow rate distribution and the existence of secondary flow in the pipe is an important factors. It will affect the accuracy of turbine flow meter measurement. Therefore, the turbine flow meter on the upstream and downstream pipe sections has certain requirements. For industrial measurement, the general requirements of the upstream 20D, and downstream 5D straight pipe length. To eliminate the secondary flow, it is best to add a rectifier at the upstream end. If the upstream end can ensure that there is about 20D straight pipe section, and add the rectifier, the flow meter measurement will be more accurate.
- Turbine flow meter on the cleanliness of the fluid has high requirements. In front of the flow meter must be installed to ensure the cleanliness of the fluid filter. The filter can be used funnel-type, and its cleanliness can be measured at both ends of the differential pressure change.
- To ensure that the liquid through the flow meter is single-phase, that is, can not let the air or vapor into the flow meter, upstream of the flow meter should be equipped with a degasser if necessary. For easy to gasify the liquid, the flow meter downstream must ensure a certain back pressure. The size of the back pressure can be taken as the maximum flow rate under the flow sensor pressure drop of two times plus the highest temperature under the measured liquid vapor pressure of 1.2 times.
Method 3: Adopting the Anti-interference Cable
To ensure that the display instrument on the turbine sensor output pulse signal has sufficient sensitivity, we must improve the signal-to-noise ratio. To this end, the installation should prevent a variety of electrical interference phenomena, namely electromagnetic induction, electrostatic, and capacitive coupling. Therefore, in the configuration of the signal transmission line, the following points must be noted:
- Limit the maximum length of the signal line. The maximum length of the signal line is, L = dV; in which, V is the minimum flow when the sensing coil output voltage RMS value, mV; d for the coefficient, m/mV, the value can be taken: V <1000 mV, d = 1.0; 1000 mV <d <5000 mV, d = 1.5; V> 5000 mV, d = 2.0.
- Signal line should be used for shielded cables to prevent inductive noise from the outside.
- The signal transmission line should be shielded cable to prevent induction noise from outside. The transmission cable is required to be shielded and grounded at the end of the display instrument. The transmission cable should not be close to the strong electromagnetic equipment, and it is not allowed to travel with the power line.
Some Requirements for Accurate Measurement
- Requirements for piping:
Flow meter installation point of the upstream and downstream piping with the same inner diameter of the flow meter.
- Requirements for the bypass pipe:
To ensure that the flow meter maintenance does not affect the normal use of the medium, the cut-off valve (shut-off valve) should be installed on the pipeline before and after the flow meter. Besides, it should be set up at the same time bypass pipe. Flow control valve to be installed in the flow meter downstream, the flow meter used upstream of the shut-off valve installed must be fully open to avoid the upstream part of the fluid producing an unsteady flow phenomenon.
- Requirements for impurities in the medium:
To ensure the service life of the flow meter, should be installed in the flow meter before the straight section of the filter.
- Requirements for the external environment:
The flow meter is best installed indoors, must be installed outdoors, and be sure to use the sun, rain, and lightning protection measures, so as not to affect the service life.
- Installation place:
The flow meter should be installed for easy maintenance, with no strong electromagnetic interference and heat radiation.
- Requirements for the installation of welding:
The user with another pair of standard flanges welded to the front and rear pipeline. Do not allow welding with the flow meter. To ensure that the flow meter is not damaged during use. When installing the flow meter, the sealing gasket between the flanges can not be recessed into the pipe. The following is according to the specific classification to talk about the installation.
- Clamping type. The sensor itself has no flange. It is by the pipe on the flange clamped sensor on the two sealing end faces, easy to install. However, it does not apply to higher pressure and larger caliber.
- Flange connection type. The sensor is connected to the pipeline in the form of a flange. Stereotyped products flange according to national standards. Pressure is limited to 6.3Mpa or less.
- Threaded connection type. The sensor is connected to the pipeline in the form of a thread. Threads have sealed pipe threads and non-sealed pipe threads of two kinds. They can withstand high pressure, but not for larger caliber.