What do 4~20mA and passive/active mean for electromagnetic flowmeters?
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What do 4~20mA Passive active mean in the E+H flowmeter samples? The instrument itself is already a 4-wire system that requires external power supply; then why are there active and passive types?
. 4~20mA, standard current analog signal； Passive / active, driven / active. The HART protocol is a master/slave protocol; the intelligent field (slave) device will send signals only when the master device sends a signal. If two field devices need to communicate with each other, it is necessary to set a master-slave mode for the two devices. The HART protocol is generally not suitable for use as a control signal directly (due to insufficient speed and reliability; it was designed solely for the remote intelligent control of analog signal devices). Therefore, the HART protocol provides two channels for synchronized communication: a 4 - 20mA analog signal and a digital signal. The 4 - 20mA signal uses a 4 - 20mA current loop (the most reliable industry standard) to transmit the main measurement values. Additionally, HART uses digital signals superimposed on the analog signal to transmit information about other devices. .
This is the question of who is responsible for powering the circuit.
Yes, external power supply makes the system active, while power supply from the system’s own circuit makes it passive:$