To check the stability of the electromagnetic flowmeter, we have to operate under controlled conditions and must be regularly tested. The flow industry's middle and small-caliber flow meters are generally equipped with bypass pipes and corresponding shut-off valves. Once the meters are commissioned and put into operation, they are generally not allowed to stop the water supply. Therefore, it is not possible to remove the flow sensors and send them to the laboratory offline. Verify on the flow standard device. In order to make the measurement of the electromagnetic flow meter correct and reliable in a certain period of time without affecting the pipe network water supply, the water supply industry often adopts an online inspection and verification method instead of regular off-line cycle verification.
1, 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 500V DC megohmmeter. If the liner adhesion layer must 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.
2, 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 and cause the converter to drift, affecting the measurement accuracy. In practice, because of negligence, the junction box is not sealed, such as the installation of sealing gaskets at the end of the cable lead, the introduction of moisture, so that the insulation drop of the terminal is a frequent case of failure. 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.
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.
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 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.
Galvalume Steel Coil
Galvalume steel is also called Aluminum-Zinc Alloy Coated Steel, Zincalume steel, aluminized zinc steel (aluzinc steel), SGLC. The galvalume metal is composed of 55% aluminium, 43.4% zinc and 1.6% silicon solidified at a high temperature of 600 ° C. Its whole structure consists of aluminium-iron-silicon-zinc, forming a dense quaternary crystal of an alloy.From the point of view of the degree of coating, the Galvanized Steel Coil is mainly the zinc plated on the coating, while the coating of the galvalume Steel Coil not only has zinc, but also has an extra part of aluminum.Galvalume Steel Sheet (coil) has better atmospheric corrosion resistance.