Electromagnetic Flowmeter System Performance Parameters And Selection

Key performance parameters of electromagnetic flowmeters include measurement accuracy, repeatability, flow rate range, range ratio, medium temperature range, pressure rating, and conductivity requirements. The measurement accuracy is usually up to ±0.5% of the indicated value, and some products can reach ±0.2% or ±0.15%. Repeatability can reach 0.2% of the indicated value [8-9]. Flow rates typically range from 0-10 m/s, with some products having a lower limit of 0.3 m/s. The range ratio can reach 1500:1, and some products are 40:1. The media temperature range depends on the lining material, e.g. 0 to +70°C for hard rubber, –20 to +50°C for polyurethane, and -20 to 70°C for PTFE. Pressure ratings up to PN. Conductivity requirements are typically ≥5 μS/cm, and some products can be as low as ≥1 μS/cm.

The selection of electromagnetic flowmeters should take into account the characteristics of the medium, lining and electrode materials, as well as the environment and installation requirements. The characteristics of the medium are the basis of selection, and the corrosiveness, abrasiveness, solid content and conductivity of the medium need to be considered. For highly corrosive media, corrosion-resistant liners such as PTFE (polytetrafluoroethylene) and corrosion-resistant electrode materials such as Hastelloy alloy and tantalum should be selected. For slurries containing solid particles, wear resistant linings such as polyurethane and ceramics should be selected, and attention should be paid to the selection of flow rate to avoid excessive wear.
The selection of lining and electrode materials needs to be comprehensively determined according to the characteristics of the medium, temperature, pressure and other factors. Common lining materials include corrosion-resistant PTFE/Teflon, wear-resistant polyurethane, and economical rubber.

Environment and installation requirements are also the key to selection, including pipeline diameter, installation environment, power supply method and communication requirements. The installation environment should consider whether explosion-proof certification is required and whether the IP68 degree required for submersible or buried installations is required. During installation, the length of the front and rear straight pipe sections should be guaranteed, usually requiring the length of the front straight pipe section to be greater than 5 times the pipe diameter, and the length of the rear straight pipe section to be greater than 2 times the pipe diameter. The power supply method can be mains power or battery power, and the battery-powered type is suitable for situations without mains power, such as field pipe networks, with a maximum battery life of up to 15 years. Communication requirements include 4-20mA analog signal output, as well as fieldbus protocols such as HART, Modbus, Profibus-PA/DP, PROFINET, etc. ...