LDE-100 electromagnetic flowmeter online inspection

Case introduction

LDE-100 electromagnetic flowmeter is widely used in process industries and public utilities, according to the requirements of the measuring instrument must be in a controlled state of operation and regular calibration, flow meter flow value checking method usually offline and on-site online inspection of two kinds of methods, because both methods have defects, in practice, the majority of users to explore a number of indirect checking methods in the field, verification or assessment of the electromagnetic flowmeter flow measurement value has exceeded the original calibration level range to provide a basis for continued use or the need for further inspection. The original calibration level range, for continued use or the need for further inspection to provide a basis. LDE-100 electromagnetic flowmeter online inspection of the current situation is still a lack of comprehensive understanding of the electromagnetic flowmeter online inspection, only to see a few Japanese companies in recent years published the implementation of non-solid flow online inspection reports; in addition, Shanghai region a few years ago, has begun to explore and formulate the ‘on-line inspection methods’ and so on. 1. Electromagnetic flowmeter for chemical industry In the chemical industry in the application of flow control based on the measured fluid to acid, alkaline liquid and slurry mostly, mostly corrosive and abrasive. Electromagnetic flowmeter malfunction and failure in practice, mostly due to corrosion and leakage, electrode contamination or attachment of foreign objects caused by. Electromagnetic flowmeter traditional periodic maintenance inspection is the flow sensor unloaded pipeline cleaning and inspection, and then the implementation of flow calibration, in order to reduce the flow sensor from the pipeline unloading damage to the lining, the first in the pipeline to measure the edge of the resistance and so on to deduce the existence of anomalies, and then decide on the next step of the next step of whether or not to unload the pipeline to check or real flow flow calibration. Mitsubishi Chemical Corporation (Co., Ltd.) three inspection methods accounted for the proportion of: (1) only online inspection accounted for 35%; (2) remove the pipeline for the liquid parts of the clean inspection accounted for 22%; (3) offline for the flow calibration accounted for 43%. 2. water industry (1) (Japan) Tokyo Metropolitan Waterworks Bureau of the Tokyo Metropolitan Waterworks Bureau of the electromagnetic flowmeter every year to do a comprehensive inspection, the inspection content is: visual inspection, converter characteristics test, measurement value, calibration, measurement of the voltage, measurement of each part of the flowmeter, the measurement of the electromagnetic flowmeter, and the measurement of the electromagnetic flowmeter, and the measurement of the electromagnetic flowmeter, and the measurement of the electromagnetic flowmeter, and the measurement of the electromagnetic flowmeter, and the measurement of the electromagnetic flowmeter, and the measurement of the electromagnetic flowmeter. Calibration, measurement of each voltage, measurement of edge resistance, and confirmation of the circuit. Instrument inspection and adjustment due to characteristic drift, adjustment of characteristics is very important, and ‘online adjustment’ must stop the measured medium flow, but it is not easy to do. Therefore, we can only perform the calibration of the transducer at the site without checking the operation of the transducer. The results of this check are compared with historical data to determine whether the instrument should continue to be used, repaired or new. Sensors according to the measured degree of deterioration of the excitation coil edge resistance to determine the new or not (2) Shanghai Water Supply Company and raw water companies since the 1990s, the Shanghai Water Supply Company and raw water companies began to explore online inspection and verification of the presence of anomalies in the method. No out-of-service possible pipelines were checked flow sensors and converters, with analogue signals and other general-purpose instrumentation to test the converter, with a more calibrated **** degree (depending on the degree of analogue signals), the method is the same as the offline inspection.

Sensor inspections are carried out indirectly by testing the electrode contact resistance, checking the edge and copper resistance of the excitation coil, including the excitation connecting cables, as well as checking the excitation current at the output of the transducer and checking the magnetic field strength. Pipelines with out-of-service conditions can also be accessed through a pre-set entry hole near the sensor to check the electrode and lining for fouling/deposits and cleaning. On-site inspection content on-site online inspection of electromagnetic flowmeter content as shown in Table 1. In addition to the characteristics of the check, are the flow sensor, converter and connecting cable 3 parts are carried out separately 1. characteristics of the whole machine check (No. 1) This check requires the flow sensor measuring tube filled with liquid and no flow, but this can not be done in many sites. If this is not possible, the characteristics of the entire machine can only be checked and adjusted by abandoning the whole machine, and only a single characteristics of the converter can be checked and adjusted. Must be checked in the sensor, and to ensure that the sensor excitation circuit and the signal circuit edge resistance is normal (including cable) under the premise of the significance, otherwise the whole machine can not operate normally. Usually a single feature of the converter is a negative value, the value is also very small, if the *** value is greater than 5% of the full scale, it is necessary to do a check, to confirm the cause and then make adjustments. Typically, the difference between the characteristics of the entire electromagnetic flowmeter and the characteristics of the converter sheet is less than 1%. Greater than 5% of the characteristics of many cases is the user in the pipeline valve closure is not properly adjusted due to poor conditions. 2. connecting cable inspection (No. 2) this inspection method is the same as the offline inspection, check the signal line and the excitation line of each core conduction and edge resistance, check the shield grounded or not intact. 3. converter inspection (No. 3, 4) this inspection method is the same as the offline inspection. On-site or in the instrumentation room with general-purpose instrumentation and flowmeter models to match the analogue signals instead of sensors to provide flow signals for tuning **** and calibration. Calibration includes feature checking and adjustment, setpoint checking, excitation current measurement, current/frequency output checking, and so on. Some of the check items should be compared with the recorded value of the last check (or factory value) to see whether there is any change or whether the change exceeds the permissible range.4. Flow Sensor Inspection (Serial No. 5 to 11) Indirectly evaluates whether there is any change in the magnetic field strength by inspecting the excitation coil and checking the excitation current measured by the converter; measures the electrode contact resistance to evaluate the electrode surface subjected to fouling and the condition of the lining adhering layer; Check the *** edge resistance of each part to determine the degree of deterioration of the piece and estimate whether it will be introduced as a result. If it can be taken out of service, observe and measure the thickness of the electrode and lining adhesion layer to estimate the change in flow value introduced by the change in flow area before and after cleaning the adhesion layer. (1) Measure the copper resistance of the excitation coil Measure the coil resistance with a degree digital multimeter or a Whisden bridge, make temperature coefficient corrections if necessary and compare with the instrument archive value. Confirm that the coil is conducting well and there is no short circuit between turns. (2) check the excitation coil edge resistance excitation coil and its terminals damp excitation circuit to the ground edge down, it is likely that the excitation signal into the flow signal transmission circuit, so that the electrode plus a larger edge resistance and signal resistance to the excitation voltage divider, the formation of a larger common mode signal. When this high signal exceeds the suppression capability of the converter preamplifier, it can cause the converter characteristics to drift. When the drop in edge resistance is not very serious, this phenomenon is not yet easily noticeable when the instrument is running. In addition to IP68 no terminal box, in practice, due to negligence, the terminal box is not sealed into the moisture, the terminal edge resistance drops to 5 ~ 6MΩ below the failure is easy to cause. Blow dry the terminals, usually the fault can be eliminated. (3) check the electrode resistance to liquid flow sensor electrode resistance to liquid should be measured immediately after the commissioning of the newly installed instrument, and recorded. Subsequently, every maintenance times to measure times, analyse and compare these data to help determine the cause of instrument failure. Electrode and liquid contact resistance depends on the contact surface of the measured liquid conductivity. Different media measured resistance value is significantly different. Electrode to liquid resistance can be pointer multimeter in the measurement of the tube filled with liquid, respectively, to measure the resistance between each electron and ground.

Experience has shown that the difference between the contact resistance values of the two electrodes measured separately should be less than 10% to 20%, otherwise it indicates a fault. Measured electrode contact resistance compared with the original measured value, if inconsistent, there may be the following three different tendencies: (a) the two electrodes marginally attached layer coverage is inconsistent, or an electrode signal loop edge resistance drop; (b) resistance value increases, the reason is that the electrode surface is covered by the edge layer; (c) resistance value decreases, the reason is that the electrode near the surface of the lining attached to the conductive deposition layer, or the electrode assembly (such as the edge of the ferrule) edge drop. Sometimes, although the above phenomenon, but did not form a fault, it can be used as a precursor to predict the failure, should be taken in advance of the relevant measures. Pointer-type multimeter to measure the electrode resistance should be noted: (a) resistance value should be read in the instant the probe contact terminal pointer deflection value, the measured value should be based on the initial. Such as re-measurement due to the chemical effect of the measured values are inconsistent. (b) measure the resistance value of the two electrodes, the grounding end of the rod characteristics must be the same, that is, fixed with the meter with the rod connected to the electrode, the other rod is always grounded. (c) to compare the regular check before and after the two measurements, you must use the same type of multimeter, and with the same **** range, commonly used 1.5V battery operating range file, such as ‘× 1kΩ’ file. Measurement of electrode contact resistance with a multimeter is only to determine the general value. Accurate measurement must be used digital bridge or AC bridge (such as Kohlraush bridge, etc.). (d) Measurement of Electrode/Liquid Intercalation Voltage Measurement of this voltage will help determine whether the electrodes are fouled or covered, whereby a fault with unstable characteristics or wobbly output may develop. With a digital multimeter 2V DC file were measured between the two electrodes and ground chemical voltage (electromagnetic flowmeter can be measured without power, can also be measured without power). The size of the chemical voltage is determined by the electrode potential of the electrode material and the nature of the liquid, the measured value may be between a few millivolts and hundreds of millivolts. If the electrode attached to the metal powder during operation will change the potential; metal powder alternately attached / detached from the electrode will also make the output unstable. Table 2 shows the natural potentials of several metals in seawater. (e) check the signal circuit *** edge and the excitation circuit / signal circuit between the edge of the check is also to assess whether the introduction of *** edge drop, check the signal circuit, the signal line to be temporarily disconnected from the electrode, the occurrence of *** edge drop for many reasons, such as junction box is not sealed into the moisture and IP68 protection type sensor cable cut and then connected to not do a good job of moisture treatment, etc. caused by. (f) check the electrode edge resistance and lining condition of this check for small calibre instruments can only be unloaded pipeline, for large calibre instrumentation is emptied after the accumulation of liquid (water), you can enter the pipe from the hole into the observation, drying the inner surface of the lining, with a 500VDC megohmmeter to test the two electrodes on the ground edge resistance respectively. If the liner has an adherent layer must be removed, according to the thickness of the layer selected for future cleaning intervals. If the conductivity of the attached layer is the same as the liquid and is not thick, the additional error of the area change can be ignored; if the conductivity of the attached layer is less than the liquid will produce a positive additional error; vice versa, a negative additional error. General requirements of the electrode edge resistance greater than 100MΩ, most of the edge of the reason for the decline is the electrode, bushings, etc. by the outside world, such as water immersion due to moisture, and sometimes with hot air blowing to exclude moisture can be restored. If the edge of the destruction (such as corrosive fluid from the seal invasion), can only replace the sensor, back to the manufacturer for repair. Four online inspection of the development of trends 1. Develop online inspection of regulatory documents in the Shanghai area water companies and raw water companies in the electromagnetic flowmeter manufacturer with the cooperation of the exploration and accumulation of more than 300 units of large-calibre electromagnetic flowmeter checking experience, and 1997 to 1998 during the drafting of the ‘large-calibre electromagnetic flowmeter on-line calibration methods,’ the Shanghai Municipal Public Utilities Administration of the enterprises belonging to the trial implementation. Now the Shanghai Water Bureau is based on this document to develop ‘electromagnetic flow meter online calibration specifications’ local industry standards.