Daily maintenance (1)
Only need to periodically check the instrument, check the environment around the instrument, remove the dirt, ensure that no water and other substances are inspected, check whether the wiring is good, check whether there is a new strong electromagnetic field device near the instrument or a new installed wire across the instrument. If the measuring medium is easy to contaminate the electrode or precipitate or scale in the measuring tube wall, it should be regularly cleaned and cleaned.
Folding fault finding
After the flowmeter starts to be put into operation or is put into operation for a period of time, it is found that the instrument is not working properly. First, check the external condition of the flowmeter, such as whether the power supply is good, whether the pipeline is leaking or is in a state of non-full pipe, whether there is air bubble in the pipe, whether the signal cable is Damage, converter output signal (ie rear position meter input loop) is open circuit. Remember to blindly disassemble the flowmeter.
Sensor check
Test equipment: one 500MΩ insulation resistance tester, one multimeter.
Test steps:
(1) When the pipeline is filled with medium, measure the resistance between terminals A, B and C with a multimeter. The resistance between A-C and B-C should be equal. If the difference is more than 1 time, there may be leakage of the electrode, condensation on the outer wall of the measuring tube or the junction box.
(2) In the case of lining drying, measure the insulation resistance between A-C and B-C with MΩ meter (should be greater than 200MΩ). Then use a multimeter to measure the resistance of the two electrodes in terminals A and B and the measuring tube (should be in short-circuit communication). If the insulation resistance is small, indicating that the electrode is leaking, the entire flowmeter should be returned to the factory for repair. If the insulation is reduced but there is still more than 50 MΩ and the inspection result of step (1) is normal, the outer wall of the measuring tube may be damp, and the inside of the outer casing may be dried by a hot air blower.
(3) Use a multimeter to measure the resistance between X and Y. If it exceeds 200 Ω, the excitation coil and its lead wire may be open or poorly connected. Remove the terminal block check.
(4) Check the insulation resistance between X, Y and C, which should be above 200 MΩ. If it is lowered, dry the inside of the casing with hot air. In actual operation, the decrease in coil insulation will result in increased measurement error and unstable instrument output signal.
(5) If it is determined that the sensor is faulty, please contact the manufacturer of the electromagnetic flowmeter. The general site cannot be solved and needs to be repaired by the manufacturer.
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
Volumetric flowmeter
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 V-cone flowmeter is a new generation of differential pressure flow measuring instrument. In practical use, many factors have a great influence on the measurement accuracy of the differential pressure flowmeter, which increases the measurement error and reduces the accuracy.
The specific performance is as follows:
1) the design parameters are inconsistent with the working parameters;
2) there is no temperature compensation or compensation is incorrect;
3) the length of the upper and lower straight pipes is insufficient;
4) the cones and pipes are not concentric;
5) the pressure pipes Blockage, etc.
After on-site inspection, the shortage of straight pipe sections, disagreement, and blockage of the pressure guiding pipe can be ruled out.
The differential pressure transmitter is removed for verification, the transmitter is qualified, and the error is within the allowable range.
The technicians recalled the trend record of DCS preservation, and looked at the steam temperature and pressure recording curve. The temperature was between 120 °C and 150 °C, the pressure was between 0.3MPa and 0.6MPa, and the measured temperature and pressure deviated from the design value. The design parameter was temperature. 193 ° C, pressure 1.13 MPa). At the same time, the DCS configuration was viewed and it was found that there was no temperature and pressure compensation for the steam flow in the configuration.