How Are Small Signals Generated in Electromagnetic Flowmeters?

An electromagnetic flowmeter is based on Faraday's law of electromagnetic induction, calculating fluid flow by measuring the induced electromotive force of a conductive fluid in a magnetic field. Electromagnetic flowmeters typically consist of a transmitter and a converter. The flow rate of the measured medium is converted into an induced electromotive force by the transmitter, which is then converted by the converter into a unified standard signal (4-20 mA output) for indication, recording, or integration with electric unit combination instruments. In actual measurement sites and process flows, electromagnetic flowmeters may exhibit errors and are susceptible to interference, such as the "small signal" phenomenon, mainly due to the following issues in use:

1. Due to external vibration or strong magnetic field interference, when there is no medium flow, external vibration and other signals act on the sensor, introducing a "false flow" signal. When this signal exceeds the meter's lower measurement limit, it is also accumulated.

2. An insulating substance adheres to the electrode surface, external interference occurs, or the millivolt signal sent from the electrode experiences zero drift during amplification and conversion, causing the signal to deviate from the normal value, thereby resulting in errors.

3. When the pump starts, the liquid passes through the flowmeter and cuts the magnetic field lines, generating a flow signal. These liquids are ultimately utilized by downstream processes, and the flow measurement value is valid and should be accumulated. When the pump stops, a small amount of liquid may flow back in the pipeline, cutting the magnetic field lines in reverse, also generating a small signal. However, these liquids are not actually used in production, yet the flowmeter still transmits the signal to the PLC for sampling and accumulation, which can cause significant errors.