E+H electromagnetic flowmeter excitation coil, electrode, lining inspection points

Case introduction

　　E + H electromagnetic flowmeter fault check the main parts of the instrument is also the main and key parts of the structure, E + H electromagnetic flowmeter key for the instrument to determine the nature of the measurement data of the components first on the excitation coil, and then is the electrode and the lining, the instrument is a whole measurement system, each component needs to be in good working condition in order to ensure that the accuracy of the output results. For the excitation coil inspection project is to check the excitation coil and its converter measured excitation current in order to indirectly evaluate whether the magnetic field strength changes; for the measurement of the electrode inspection focuses on the electrode of the liquid resistance to assess the electrode surface by the dirt and the lining of the adhesion layer condition; check the insulation resistance of each part to determine the degree of deterioration of the parts in order to assess whether it will lead to interference; lining of the inspection focuses on the ability to stop media flow conditions in the pipeline can be observed. The lining inspection focuses on the thickness of the electrode and lining adhesion layer that can be observed and measured in the pipeline under the flow condition, so as to estimate the change of flow value introduced by the change of flow area before and after cleaning the adhesion layer.

　　First, check the excitation coil copper resistance: with a high degree of digital multimeter or Whisden bridge to measure the coil resistance, if necessary, the temperature coefficient correction with the instrument file value comparison. Confirm that the coil is conducting well and there is no turn-to-turn short-circuit phenomenon.

　　Second, check the insulation resistance of the excitation coil: the excitation coil and its terminals damped excitation circuit insulation to ground declines, it is likely to introduce the excitation signal into the flow signal transmission circuit, so that the electrode plus a larger insulation resistance and signal resistance to the excitation voltage divider, the formation of a large common-mode interference signal. When this interference signal exceeds the suppression capability of the converter preamplifier, it will cause the converter zero to drift. When the insulation resistance drop is not very serious, this phenomenon is not easy to detect 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 insulation resistance drops to 5 ~ 6MΩ below the failure is easy to cause. Blow dry terminals, usually the fault can be eliminated.

　　Third, check the electrode resistance: E + H electromagnetic flowmeter sensor electrode resistance should be measured immediately after the commissioning of the newly installed instrument, and recorded. Measured once every subsequent maintenance, analysis and comparison of 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. There is a significant difference between the resistance values measured for different media. Electrode contact resistance can be used pointer multimeter in the measurement of the tube filled with liquid, respectively, to measure the resistance between each electron and ground. Experience shows that the difference between the contact resistance of the two electrodes measured separately should be less than 10% to 20%, otherwise it indicates a failure. Measured electrode contact resistance with the original measured value if there is a difference, the reasons are: a, the two electrodes insulating adhesion layer covering inconsistency or an electrode signal loop insulation resistance decreased; b, the resistance value increases is the electrode surface is covered by an insulating layer; c, the resistance value decreases is the electrode near the surface of the lining attached to the conductive deposition layer or electrode assembly (such as insulating rings) insulation decreased. Sometimes not a fault, but should be taken as a precursor to the fault and take appropriate measures.

　　Check the polarisation voltage between the electrodes/liquid: Measuring this voltage will help to determine whether the electrodes are fouled or covered, which could result in a faulty zero point or wobbly output.

　　V. Checking the insulation of the signal circuit and the insulation between the excitation circuit/signal circuit: The purpose of this check is to assess whether interference has been introduced as a result of degradation of the insulation. When checking the signal circuit, the signal wire should be temporarily disconnected from the electrode. The causes of insulation degradation include the entry of moisture into the junction box without sealing, and the lack of moisture-proof treatment when the cable of the protective sensor is cut and reconnected.

　　Sixth, check the insulation resistance of the electrode and lining condition: the inspection of the small-diameter instrument to be unloaded from the pipeline, the large-diameter instrument can be emptied of liquid from the hole into the pipeline to observe: dry lining the inner surface with a megohmmeter to test the insulation resistance of the two electrodes to the ground; if there is a layer of adhesion to the lining should be cleared and according to the thickness of the accumulation of layer to determine the cleaning cycle; if the adhesion of the layer is not thick and the conductivity of the same as the liquid, then the change in the area can be ignored! Additional error; if the conductivity of the attached layer is less than the liquid will produce positive additional error, and vice versa will produce negative additional error. Electrode insulation resistance is generally required to be greater than 100MΩ, insulation decline due to the electrode, bushing, etc. by the outside world water immersion caused by moisture (with a hot air blower to exclude moisture can be); if the insulation damage (such as corrosive fluid from the seal invasion), then the sensor must be replaced or returned to the manufacturer for repair. Sensor using non-uniform magnetic field technology and special magnetic circuit structure, magnetic field is stable and reliable, and a large reduction in volume, reduce the repetition, so that the flow meter small flow characteristics. Its full Chinese electromagnetic converter kernel using high-speed central processing unit. Calculation speed is very fast, high precision, reliable measurement performance. So that the customer ‘buy assured, with the heart, service is satisfactory’ is my company's purpose.