Research on key technology of two-wire electromagnetic flowmeter
The energy consumption of the two-wire electromagnetic flowmeter comes from the 4～20 mA current loop.If the pow-er consumption of the instrument itself is greater than the maximum energy value corresponding to the current loop equivalent current of 4mA,the loop will not be able to output the lower limit of 4mA current value.Therefore,it is generally required that the power consumption of the two-wire electromagnetic flowmeter(all circuits including sensors)should not be greater than 96mW(4 mA*24V dc),which is one of the fundamental principles of the two-wire instrument[1].In order to ensure that the 4～20mA output function is normal,the maximum power taking current of the 4～20 mA current loop is usually set to 4mA,and the corresponding maximum power is 96mW.When the current output is greater than 4 mA,in addition to the energy corresponding to 4 mA obtained by power,the rest of the energy greater than 4 mA is diverted and directly wasted.This characteristic determines that the energy pro-vided to the two-wire flowmeter itself is very limited,and the excitation current must be at a lower level,resulting in the overall weak comprehensive performance of the two-wire electromagnetic flowmeter compared with the four-wire flowmeter.If the power-on state is dynamically adjusted according to the change of the 4～20 mA output current state of the two-wire electromagnetic flowmeter,the greater the output current is,the more energy will be obtained,and vice versa.Then use the obtained energy to increase the excitation current of the flowmeter,which can improve the measurement performance of the two-wire electromagnetic flowmeter to a certain ex-tent,improve the measurement accuracy of the instrument,and enhance the adaptability of the instrument to working conditions.
Two-wire electromagnetic flowmeter4～20ma current loopdynamic power supplyexcitation current
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