Electromagnetic flowmeter can accurately measure the fluid flow, but how to solve the measurement of the "small signal" problem, is also an important factor affecting the accuracy of measurement.
With the increasing automation and intelligence of industrial production processes and the requirements for energy saving and cost accounting management, flow meters account for an increasingly larger proportion of the entire metering instrumentation. Although electromagnetic flow meters can accurately measure fluid flow, how to solve the "small signal" problem that occurs during measurement is also an important factor affecting accurate measurement.
1. Reasons for small signals Electromagnetic flowmeters have errors and are easily interfered with in actual measurement sites and process flows, such as the "small signal" phenomenon. From the working principle of electromagnetic flowmeters, it can be seen that the interference problem of electromagnetic flowmeters is caused by various excitation methods. At present, many factories have the following problems:
1. When the working pump starts, the liquid passes through the flowmeter and cuts the magnetic lines of force to generate a flow signal. These liquids are used in subsequent links, and the flow measurement value is valid and should be accumulated. When the pump stops, a small amount of liquid will flow back in the pipeline and cut the magnetic lines of force in the opposite direction, also generating a small signal. However, these liquids are not used in actual production, and the electromagnetic flowmeter will still transmit the signal to the PLC for sampling and accumulation, which will cause a large error.
2. Due to external vibration or large magnetic field interference, when there is no medium flowing, external vibration and other signals act on the sensor, introducing a "false flow" signal. When this signal is higher than the metering lower limit of the instrument, it is also accumulated.
3. The electrode surface is adhered to a layer of insulating material, is disturbed by the outside world, or the milliampere signal sent by the electrode has zero drift during the amplification and conversion process, causing the signal to deviate from the normal value, thus causing errors. All of the above phenomena belong to small signal phenomena.
2. Small signal processing measures The small signal problem caused by interference signals cannot be solved from the process design, and can only be solved from the process control aspect. It can be processed by 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 enterprise, because there will be many electromagnetic flow meters in a work section, so many such meters need to be replaced accordingly.
2. The software method can be realized through PLC software, and the small signal problem can be solved by parameter setting.
Hangzhou Economic Development Area，Hangzhou 310018，China
