Dynasonics Fusion Water Flow Meter - Manual (Page 14)

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The 4-20 mA output is designed to source current across a loop
resistance that is typically located within a data acquisition
system or other receiving instrument. The maximum resistance
that the FUSION can accommodate is directly related to the DC
power source that is powering the flow meter and the 4-20 mA
loop. Figure 8 illustrates the range of load resistance that can be
used with a given power supply voltage. Ensure that the loop
load resistance is within the shaded region of the graph, or non-
linearity and transmitting errors will occur.
The 4-20 mA output is polarized and since the output shares the
DC common with the power supply, reversing the connections
can cause a short circuit in the DC power circuit. Figure 9 shows
a block diagram of how the 4-20 mA interfaces with the receiving
device.
FUSION Flow Meter Receiving Device
Meter Power 12 to 30 Vdc
Power Supply
Ground
Loop Resistance
4-20 mA
4-20 mA Output
Signal Ground
Figure 9
4-20 mA Block
Diagram