SMAR HI302, User Manual

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HI302 - User’s Manual
2.7
HI302-I (4-20 mA to FF Conversion)
This kind of topology doesn’t have necessarily the 250 Ω external resistor connected in
series with each device, since there is a 4-20 mA sampling resistor on the HI302 analog
board serial to the loop. Be careful with a short-circuit in the loop, because the HI302’s
internal resistor may be damaged. The HI302 does not have internal protection against
short-circuit.
HI302-O (FF to 4-20 mA Conversion)
It is not necessary to use a resistor in series with the power supply in this topology,
because the device internal impedance and the actuator impedance ensures the minimum
requirement for HART comunication. However, the user should watch the minimum supply
voltage required for total impedance (including the wiring impedance). In this topology, the
HI302’s output is protected against short-circuit.