170
Reference Manual
00809-0100-4026, Rev HA
Section 8: Safety Instrumented Systems (4-20 mA Only)
November 2014
Safety Instrumented Systems (4-20 mA Only)
The HART loop must be referenced to ground in one point located between the power supply
and the load resistor. Either the negative or the positive pole of the power supply can be ground
referenced, depending on the placement of the load resistor. See Figure 8-1 as an example.
Figure 8-1. Reference Ground when the Load Resistor is Inserted in the Negative Line
Table 8-2. Minimum Input Voltage (U
i
) at Different Currents
Hazardous approval
Current
3.75 mA 21.75 mA
Minimum input voltage (U
i
)
Non-hazardous Installations and
intrinsically safe installations
16 Vdc 11 Vdc
Explosion-proof / flameproof
installations
20 Vdc 15.5 Vdc
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