Fluke 789 - Manual (Page 37)

ProcessMeter™
Loop Power Supply Mode
29
Loop Power Supply Mode
The Loop Power Supply Mode can be used for powering
up a process instrument (transmitter). While in Loop
Power Mode, the meter acts like a battery. The process
instrument regulates the current. At the same time, the
meter measures the current that the process instrument is
drawing.
The meter supplies loop power at a nominal 24 V dc. An
internal series resistance of 250
Ω can be switched in for
communication with HART and other smart devices by
pressing J (Blue). Pressing J (Blue) again switches out
this internal resistance.
When loop power is enabled, the meter is configured to
measure mA and > 24 V dc is sourced between the mA
and A jacks. The mA jack is the common and the A jack is
at > 24 V dc. Connect the meter in series with the
instrument current loop as Figure 10 shows.
32
30
28
26
24
22
20
0 4 8 12 16 20 24
Loop voltage w/ 250 Loop voltage w/o 250
Voltage (V)
Current (mA)
anw020f.eps
Figure 9. Loop Power Voltage vs. Current