What checks should be done before using an electromagnetic flowmeter?

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Hi, your industrial control assistant is here as scheduled. Today, we’re going to share some basic information about electromagnetic flowmeters. Thanks to their numerous advantages, electromagnetic flowmeters are being used more and more often these days. So, we’ll introduce the preparatory work and inspections that need to be done before using electromagnetic flowmeters. 1. To check the copper resistance of the excitation coil of the electromagnetic flowmeter, use a high-precision digital multimeter to measure the coil resistance; a temperature coefficient correction may be necessary. By comparing the measured values with the instrument’s archive values, it is confirmed that the coil is in good conductive condition without any inter-turn short circuits or similar issues. In fact, the probability of inter-turn short circuits in the coil is very low. Together with the converter excitation current check, this inspection can indirectly assess whether there is any change in the magnetic field strength of the flow sensor. 2. Check the insulation resistance of the excitation coil of the electromagnetic flowmeter. When the excitation coil and its connection terminals become damp, the insulation of the excitation circuit with respect to ground decreases, which can introduce common-mode interference signals, cause the converter’s zero point to shift, and affect measurement accuracy. In practice, due to carelessness, the junction box is not properly sealed; for example, it is common for sealing washers to be omitted at the cable entry points, allowing moisture to enter and resulting in a decrease in the insulation of the terminal connections. Dry the terminals with a hot air blower; usually, the insulation can be improved or restored to its original level at the time of manufacture, and the fault will be resolved. 3. Inspection of electrode contact resistance: By measuring the contact resistance between the electrodes and the liquid, it is possible to indirectly assess the condition of the electrodes as well as the overall condition of the surface of the lining layer. The electrode contact resistance of the flow sensor in Emerson’s electromagnetic flowmeters should be measured immediately after the instrument has been installed and calibrated, and the value should be recorded. In the future, a measurement should be taken after each maintenance; analyzing and comparing these data will help determine the cause of instrument failures. 4. The inspection of the insulation in the signal circuit and the excitation circuit is primarily aimed at assessing the interference caused by a decrease in insulation. When checking the signal circuit of the Emerson electromagnetic flowmeter, the signal wire must be temporarily disconnected from the electrodes. There are many reasons for a decrease in insulation, and moisture ingress due to unsealed junction boxes is a common one. That’s all for this issue. Feel free to leave comments and follow!