Figure 6. In a two-wire 420 mA circuit configuration, a 4 mA current is used to power a transducer, and an incremental 0-16 mA current
transmitted over the same pair of wires is proportional to the measured
pressure. Current output permits transmission over a long distance without
loss of accuracy due to the cable resistance. The external transistor forms
the controllable current loop. The MCA7707 controls the voltage across resistor
RA, and if a 50 value is selected, a 0.21.0 V range would have to
be set during a calibration procedure. If necessary, the programmable gain
amplifier output can be divided using resistors RB and RC.
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