What are the common small signals of electromagnetic flowmeter?

Today, the editor of electromagnetic flowmeter will share with you what are the common small signals of electromagnetic flowmeter.

1. Small signal generation mechanism

Electromagnetic flowmeters have errors and are susceptible to interference in the actual measurement site and process flow, such as the "small signal" phenomenon. It can be seen from the working principle of the electromagnetic flowmeter that the interference problem of the electromagnetic flowmeter is caused by various excitation methods. Currently, there are the following problems in many factories: (1) When the pump is started, the liquid passes through the flow meter and cuts the magnetic lines, generating a flow signal. These liquids are eventually used in subsequent links, and their flow measurement values ​​are valid and should be accumulated; When the pump stops, a small amount of liquid will flow back in the pipeline, cutting the magnetic lines in reverse, and also generating small signals. However, these liquids are not used in actual production, and the flow meter will still transmit the signal to the PLC for sampling and accumulation, then Will cause larger errors. (2) Due to external vibration or large magnetic field interference, when there is no medium flow, external vibration and other signals act on the sensor, introducing an "erroneous flow" signal. When this signal is higher than the lower measurement limit of the instrument, it is also accumulated. (3) A layer of insulation adheres to the surface of the electrode, is subject to external interference, or the milliamp signal sent by the electrode has a zero-point drift during the amplification and conversion process, causing the signal to deviate from the normal value, thereby causing errors. The above phenomena are all small signal phenomena.

2. Small signal processing measures The small signal problem caused by the interference signal cannot be solved from the process design, and the solution can only be found from the process control aspect. It can be handled in two ways: hardware and software.

(1) The hardware method can be composed of a comparison circuit and an electronic switch. This method is mainly used to filter out interference signals, but it will increase the production cost of the company, because there will be many flow meters in one section. Therefore, many such instruments must be replaced accordingly.

(2) The software method can be realized through PLC software, and the small signal problem can be solved through the process logic block diagram.