Types of electromagnetic flow meters and piping connections

　　Electromagnetic flowmeters are classified by sensor and converter assembly method:

　　1. The commonly used form of split electromagnetic flowmeter is that the sensor is connected to the pipeline, and the converter is installed in the instrument room or near the sensor where people can easily access, tens to hundreds of meters apart. To prevent the intrusion of external noise, the signal cable usually adopts double shielding. When measuring low conductivity liquids and the distance is more than 30m, in order to prevent the signal attenuation caused by the partial capacitance of the cable, the inner shield is also required to be connected to the shield drive of the low impedance source with the same potential as the core wire. The separate converter can be far away from the harsh environment on site, and it is more convenient to check, adjust and set parameters of electronic components.

　　2. Integrated electromagnetic flowmeter - the sensor and converter are assembled together to directly output a DC current (or frequency) standard signal, which actually becomes an electromagnetic flow transmitter. The integrated type shortens the connection length of the signal line and the excitation line between the two, and makes them externally connected and hidden inside the instrument, thereby reducing signal attenuation and the intrusion of space electromagnetic wave noise. The same measurement circuit can measure liquids with lower conductivity than the split type. The wiring of the signal line and the excitation line is cancelled, the electrical connection is simplified, the instrument price and installation cost are relatively cheap, and it is mostly used in small-diameter instruments. With the commercialization of two-wire instruments, integrated instruments will develop rapidly. However, if it is installed in an inaccessible place due to pipeline layout restrictions, maintenance will be inconvenient.

　　In addition, the electronic components of the converter are installed on the pipeline, which will be greatly restricted by the fluid temperature and pipe vibration. Classification by the connection method between the flow sensor and the pipeline:

　　1. Flange connection electromagnetic flowmeter - Flange connection is a traditional connection method. There are connecting flanges at both ends of the sensor, which are fixed to the pipeline flange with bolts and can be installed in one direction. Large-diameter sensors all use this connection method.

　　2. Flange clamp connection electromagnetic flowmeter - Flange clamp connection is a connection method developed in recent years. The sensor itself has no flange and is clamped between the two flanges of the pipeline with a long bolt to connect to the pipeline system. This type of sensor is small in size and light in weight, and has strong adaptability to different pressure specifications and standard pipeline flange hole distances; but it is only suitable for smaller pipe diameters (less than 200mm) and can withstand lower liquid working pressure.

　　3. Clamp-connected electromagnetic flowmeter-the clamp-type connection can achieve quick disassembly and installation, which is convenient for frequent daily cleaning.

　　4. Threaded electromagnetic flowmeter - This type of instrument is mostly used in the pharmaceutical, food and other industries and pharmaceutical proportioning injection and other places. Threaded connection is also widely used in petroleum, geological exploration and other high-pressure water injection or cement slurry flow measurement above 16-25MPa, and the thread shape is trapezoidal.