Here we talk about the daily inspection of the electromagnetic flowmeter:
1, check the excitation coil insulation resistance.
Excitation coils and their terminals are damped and the insulation of the excitation circuit is reduced. This will introduce a common-mode interference signal, which will cause the converter to drift and affect the measurement accuracy. In practice, because of negligence, the junction box is not sealed well, such as the installation of sealing gaskets at the end of the cable lead, the introduction of moisture, and the insulation drop of the terminal is a frequent failure case. Drying the terminal with a hot air blower usually insulates it to increase or restore the insulation level to the factory, and the malfunction can be eliminated.
2, check the electrode contact resistance.
Measuring the contact resistance of the electrode and the liquid can indirectly evaluate the general conditions of the surface of the electrode and the backing layer, such as whether the electrode surface and the backing layer are attached to the deposited layer, and whether the deposited layer is conductive or insulating. The electrode contact resistance of the flow sensor should be measured immediately after the new instrument is commissioned and recorded. After each maintenance measurement, analyzing and comparing these data will help determine the cause of the instrument failure.
The contact resistance value between the electrode and the measured medium depends on the size of the contact surface (ie, the size of the electrode end surface) and the conductivity of the measured medium.
3, measuring the excitation coil copper resistance.
Use a high-precision digital multimeter or Wheatstone bridge to measure the coil resistance. If necessary, correct the temperature coefficient. The measured value is compared with the instrument file value to confirm that the coil is conducting well with no short circuit between turns. In fact, there is a very low chance of a short circuit between coil turns. This check, together with the transformer excitation current check, can indirectly assess whether the magnetic field strength of the flow sensor has changed.
The measured contact resistance value of the electrode is compared with the original measurement value. If there is inconsistency, the following different trends may occur:
(1) The resistance value increases. It shows that the surface of the electrode is covered with an insulating layer.
(2) The resistance value decreases. Shows that the surface of the electrode is accompanied by a conductive deposition layer, or the electrode insulation performance is degraded.
Experience shows that the contact resistance of two electrodes is close. The difference between the two resistance values ​​should be less than 10% to 20%. Otherwise, the insulation layer of the surface of the two electrodes is not uniform, or the insulation of one electrode signal circuit is greatly reduced.
The contact resistance of the electrode can be measured by measuring the resistance between each electrode terminal and the ground when the multimeter is filled with the measured medium. The following points should be noted when measuring:
(1) When measuring the resistance of two electrodes, the polarity of the measuring rod must be the same, that is, one measuring rod is used to fix the electrode, and the other measuring rod is always grounded.
(2) The resistance value shall read the maximum value of the deflection of the pointer during the initial instant of the contact of the measuring rod with the terminal. The measured value shall be based on the initial one. Repeated measurements can cause different measurements due to polarization.
(3) When comparing the measured values ​​before and after the second periodic inspection, the same type of multimeter must be used and the same range must be used.
Measuring the electrode contact resistance with a multimeter is not a method of measuring the exact value, but a general value. Digital bridges must be used for accurate measurements.
4. Check the insulation between the signal circuit insulation and the excitation circuit/signal.
The purpose of this inspection is also to assess the interference introduced due to the degradation of insulation. When checking the signal loop, the signal line should be temporarily disconnected from the electrode. There are many causes of insulation degradation, and it is a common cause that the junction box is not sealed to enter moisture.
5. Check the electrode insulation resistance and lining condition.
To check the electrode insulation resistance, the integrity of the liner or the condition of the adhesive layer, the inspection of the small-diameter instrument can only be carried out from the pipeline. For large-diameter instruments, the measurement medium is to be vented and observed from the manhole into the pipe. Wipe off the inner surface of the electrode and lining, leaving no liquid stains and drying. Measure the insulation resistance of the two electrodes to the ground with a 500 VDC megohmmeter. If the liner adhesion layer has to be removed, the cleaning interval interval is determined according to the thickness of the laminate. A large part of the drop in electrode insulation is due to moisture or water immersion in the sensor. Sometimes it can be restored by removing the moisture with a hot air blower. If it is indeed the destruction of the insulation, such as the leakage of the electrode, the sensor can only be replaced and returned to the manufacturer for repair.
Changzhou Chengfeng electromagnetic flowmeter , the domestic high-end flow meter brand, to meet customer needs first, quality first, allowing customers to use the rest assured. The reputation of Changzhou Chengfeng electromagnetic flow meter in the industry and customer feedback are all satisfactory: high precision, durability, long service life, low failure rate, and good after-sales service. These are the customers' evaluations of us. The customers' recognition of Changzhou Chengfeng is the driving force for our progress. We are striving to develop new technologies, improve product performance, and adopt high-quality materials. We are meticulous in the quality of our products and ensure the passing rate of production inspection is 100%. . Cheng Feng instrument, only to do fine, customer satisfaction is our driving force.
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