The signal generated by the electromagnetic transmitter is very weak, so it is an important factor to make good use of the electromagnetic flowmeter to prevent the impact of external electrical interference. It must be pointed out that although the flow signal of the transmitter is only a few mV, it cannot be determined that the interference voltage generated on the pipeline will make the instrument unable to work normally. We tested that 10V and 50Hz AC voltage was added at both ends of the transmitter, and the instrument indication was still not affected. Therefore, for the grounding problem of electromagnetic flowmeter, the instrument grounding requirements cannot be blindly emphasized.
For the grounding problem of electromagnetic flowmeter, firstly, the transmitter should be electrically connected with the measured medium. This is a necessary condition for the normal operation of the electromagnetic flowmeter. Therefore, measures must be taken to meet this requirement when installing electromagnetic flowmeter on insulated pipe. Secondly, aiming at the problem of connection with reference potential. As the flowing medium of ordinary metal pipes is connected with the earth electricity, this can usually be met. Therefore, the electromagnetic flowmeter does not need a separate grounding device. However, a separate grounding device is conducive to the reliable operation of the instrument. Especially when the pipeline and medium encounter strong electrical interference, good grounding is an important factor for the normal operation of the instrument. The external interference of the transmitter is mainly the stray current in the pipeline, which is transmitted to the electrode through the medium. For example, if the high-power electrical equipment near the transmitter is unable to generate electricity due to reduced insulation or other reasons, the interference signal will be transmitted to the electrode through the medium through the equipment and pipeline. In order to eliminate the interference caused by these leakage currents, we must ground the medium in the measuring pipe of the transmitter. Two measures are generally adopted:
1. Strong leakage current and electric field effect exist in the installation environment, and the transmitter must be grounded separately. The bottom wire is connected to the grounding rod buried at a certain depth through multi strand copper wire, and the total cross section is not less than 4 mm2. In relatively wet places, grounding rods are usually purchased at a depth of about one meter.
2. When stray current is very strong, such as measuring the electrolyte flow in the pipeline near the electrolytic cell, stray current will cause serious interference. The protective flange can be installed between the transmitter and the insulating pipe at both ends of the transmitter. As with the general installation method, the protective flange is connected to the transmitter housing and measuring pipe through a well grounded grounding rod. The insulating pipe is connected with the process pipe through a copper core with an area of more than 4 mm2. Therefore, the leakage current is mainly a short circuit from the copper wire, and the interference from the measured liquid to the transmitter circuit is greatly reduced.