The electromagnetic flowmeter has a large measuring range, usually 20:1~50:1, and the optional flow range is wide; the diameter of the electromagnetic flowmeter is wider than other types of flowmeters, from a few millimeters to 3 meters; the positive and negative two-way flow can be measured. The pulsating flow rate can also be measured as long as the pulsation frequency is much lower than the excitation frequency; the meter output is linear in nature; it is easy to select the material type of the fluid contact member, and can be applied to corrosive fluids and the like. Since the electromagnetic flowmeter measures much more with suspended solids or dirt than other flow meters, the probability of failure of the inner wall adhesion layer is relatively high. If the electrical conductivity of the adhesion layer is close to the liquid conductivity, the instrument can output the signal normally, but only change the flow area to form a hidden fault of the measurement error; if it is a high conductivity adhesion layer, the electromotive force between the electrodes will be short-circuited; if it is an insulating adhesion layer The surface of the electrode is insulated to disconnect the measuring circuit. The latter two phenomena will make the meter inoperable.
Flow meter type
Instruments that measure fluid flow are collectively referred to as flow meters or flow meters. The flowmeter is one of the important instruments in industrial measurement. With the development of industrial production, the accuracy and range of flow measurement requirements are getting higher and higher, and the flow measurement technology is changing with each passing day. Various types of flow meters have been introduced to suit various applications. More than 100 flow meters have been put into use. From different perspectives, flow meters have different classification methods. There are two commonly used classification methods. One is to classify according to the measurement principle adopted by the flowmeter: the second is to classify according to the structural principle of the flowmeter.
Classified by flowmeter structure principle
A volumetric flow meter is equivalent to a standard volume container that measures the flow medium continuously. The larger the traffic, the more times the metric is, and the higher the frequency of the output. The principle of the volumetric flowmeter is relatively simple and suitable for measuring fluids with high viscosity and low Reynolds number. According to the shape of the rotary body, the products currently produced are: an oval gear flow meter suitable for measuring liquid flow, a lumbar flowmeter (Roots flowmeter), a rotary piston and a scraper flowmeter; a servo type suitable for measuring gas flow Volumetric flowmeters, membranes and flowmeters, etc.
The installation position and installation method of the ultrasonic flowmeter.
Selecting the installation pipe segment has a great influence on the test accuracy. The selected pipe segment should avoid the interference and eddy current, which have great influence on the measurement accuracy. Generally, the pipe segment should meet the following conditions:
1. Avoid installing the machine in the pump, high-power radio, frequency conversion, that is, where there is strong magnetic field and vibration interference;
2. Select the pipe section where the pipe should be uniform and dense, and it is easy to transmit ultrasonic waves;
3, to have a long straight pipe section, the upstream straight pipe section of the installation point must be greater than 10D (Note: D = diameter), downstream is greater than 5D;
4, the installation point upstream distance pump should have a distance of 30D;
5. The fluid should be filled with pipes;
6. There should be enough space around the pipeline to facilitate the operation of the on-site personnel. The underground pipeline needs to be a test well. The test well is as follows:
Ultrasonic flowmeters generally have two types of probe installation methods, namely Z method and V method.
However, when D < 200mm and the site condition is one of the following conditions, it can also be installed by the Z method:
1. When the measured fluid has high turbidity, when the V method is used to measure the signal or the signal is weak;
2. When the inner wall of the pipe is lined;
3. When the service life of the pipeline is too long and the inner wall is fouled seriously;
For those with better pipeline conditions, even if D is slightly larger than 200mm, in order to improve the measurement accuracy, the V method can be used for installation.