dynasonics TFXL, Installation And Operating Instructions Manual

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16
H. CONNECTING THE 4-20 mA OUTPUT
The TFXL is equipped with a ground-referenced 4-20 mA
output—the output shares a common ground with the power
supply. The output transmits a continuous current output that is
proportional to liquid flow rate. The output was scaled at the
Dynasonics factory and the scaling information is recorded on
the label located on the side if the TFXL enclosure. To ensure
that the instrument or data acquisition system that is receiving
the 4-20 mA signal responds properly, it must be spanned
identically to the TFXL.
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 TFXL can accommodate is directly related to the DC
power source that is powering the flow meter and the 4-20 mA
loop.
Chart 1 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.
TFXL Loop Resistance
0
200
400
600
800
1000
1200
1400
15 17 19 21 23 25 27 29
Supply: Vdc
Loop
L
o
a
d
:
O
h
m
s
Chart 1
4-20 mA Loop Load
Operate in the
Shaded Region