The choice of electromagnetic flowmeter is mainly the correct choice of the transmitter, and the converter only needs to be matched with it.
Choice of caliber and range
The diameter of the transmitter is usually the same as that of the piping system. If the piping system is to be designed, the diameter can be selected according to the flow range and flow rate. For electromagnetic flowmeters, the flow rate is suitable for 2 - 4m / s. In special cases, such as solid particles in the liquid, in consideration of wear, the optional flow rate is ≤ 3m / s, for easy to manage the fluid. Available flow rate ≥ 2m / s. After the flow rate is determined, the transmitter diameter can be determined according to qv= D2.
The range of the transmitter can be selected according to two principles: one is that the full scale of the meter is greater than the expected maximum flow value; the other is that the normal flow is greater than 50% of the full scale of the meter to ensure a certain measurement accuracy.
Temperature and pressure selection
There are certain restrictions on the fluid pressure and temperature that the electromagnetic flowmeter can measure. When used, the pressure used must be lower than the working pressure specified by the flowmeter. At present, the working pressure specifications of domestically produced electromagnetic flowmeters are:
Less than 50mm caliber, working pressure is 1.6MPa; 900 mm caliber, working pressure is 1 MPa;More than 1000mm caliber, working pressure is 0.6MPa.
If there are special requirements on the pressure resistance of the transmitter, you can negotiate with the manufacturer.
The operating temperature of the electromagnetic flowmeter depends on the lining material used, which is generally 5 - 70 ° C. Such as special treatment, can exceed the above range, such as the wear-resistant corrosion-resistant electromagnetic flowmeter produced by Tianjin Automation Instrument No.3. The transmitter allows the measured medium temperature to be -40 to 130 °C.
Selection of lining material and electrode tree material
The lining material and electrode material of the transmitter must be correctly selected according to the physical and chemical properties of the medium. Otherwise, the instrument will be damaged quickly due to the corrosion of the lining and the electrode, and the corrosive medium will easily cause an accident if it leaks. Therefore, the electrode and the lining material must be carefully selected according to the specific measurement medium in the production process.
Ultrasonic flowmeter performance characteristics
Measuring liquid: single fluid such as water, seawater, alkali, etc., turbidity less than 10000ppm, particle size less than 1mm
Pipe material: Ultrasonic penetrating full pipe such as steel, cast iron, PVC pipe, dense texture, no serious corrosion and scaling, allowing thin layer of dense lining
Pipe lining material: rubber, epoxy asphalt, fiberglass, mortar, etc., or unlined
Pipe diameter range: DN15mm~6000mm, plug-in sensor for pipe diameter DN25mm~6000mm
Flow rate range: -32m/s~0~+32m/s, bidirectional flow
Accuracy: ±1.0% of displayed value (under standard conditions). Configure plug-in sensor accuracy up to 0.5%
Signal output: 4-20mA or 0-20mA RS-485
Sensor: It is divided into external clip type and plug-in type. The standard configuration is clip-on. The maximum operating pressure of the plug-in sensor is 3 MPa.
Straight pipe length: upstream >10D, downstream >5D from pump outlet >30D (D: pipe diameter)
Display mode: 2*20 character LCD display with LED backlight
Protection level: IP65
Explosion-proof grade: ExdIIBT4
Fixed ultrasonic flowmeter power supply: AC110V, AC220V, DC8~36V or AC7~30V
Ambient temperature / humidity: Host -20 ° C ~ +80 ° C; sensor -20 ° C ~ +80 ° C or -20 ° C ~ +160 ° C optional, the sensor can be immersed in water, water depth less than 2m.
Fourth, the liquid turbine flowmeter put into operation the opening and closing sequence
1. The sequence of opening and closing of the operation
For flow sensors without a bypass line, first open the flow sensor upstream valve at a medium opening and then slowly open the downstream valve. Run at a small flow rate for a period of time (eg 10 minutes), then fully open the upstream valve, then open the large downstream valve opening to adjust to the required normal flow.
The flow sensor equipped with the bypass pipe first opens the bypass pipe valve to open the upstream valve at a medium opening degree, slowly opens the downstream valve, and closes the opening of the small bypass valve to make the instrument run for a period of time with a small flow rate. Then fully open the upstream valve, fully close the bypass valve (to ensure no leakage), and finally adjust the downstream valve opening to the required flow.
2. Activation of low temperature and high temperature fluids
The low-temperature fluid pipeline should drain the water in the pipeline before the flow, and then run for 15 minutes at a small flow rate, and then gradually increase to the normal flow. Slow down when stopping, so that the pipe temperature and ambient temperature are gradually approaching. High temperature fluid operation is similar to this.