Cleveland Motion Controls DIN Rail Amplifier MWI-13262 Ultra Series Non-Isolated REV BA - Manual (Page 17)

MAN-13262 R EV BA DIN R AIL A MPLIFIER , MWI-13262 U LTRA
2.13.2.2 A PPLICATION I NTERFACE DETAILS
The 4-20 mA output stage is designed to drive a loop current through a floating burden resistance. Examples of
driving a loop current through a floating burden resistance include: a loop powered 4-20 mA display or, the isolated
input of receiving electronics (isolated Analog to Digital input). The 4-20 mA output can also drive non-isolated (or
ground referred) burden resistances provided that the circuit that employs the burden does not connect to the isolated
common (COM, J2-3) of the amplifier.
For a better understanding as to why the burden must be floating with respect to the amplifier’s isolated common
(COM, J2-3) refer to Figure 9. This figure illustrates that the 4-20 mA OUT (J2-7) is connected to the +15V internal
supply voltage and the 4-20mA RET terminal sinks loop current toward the -15V internal supply. A truly floating
burden receives the loop current that is controlled by the amount of current sinking into the -15V supply. The
current is supplied by the +15V supply. Incorrectly connecting burden resistance between the 4 -20mA OUT and
COM (J2-3) would cause excessive current to flow. Incorrectly connecting the 4-20mA RET (J2-8) to COM (J2-3)
results in the 4-20mA current being drawn from ground and bypassing the burden resistance.
Figure 9 – 4-20 mA Output Circuit Wired for Floating Burden
While it is possible to interface the 4-20 mA current loop into circuits which do exhibit resistances between their
burden and the amplifier isolated COM, (Refer to Figure 10.), this is a less desirable configuration. If you chose to
wire the amplifier in this way, you must keep the following in mind. When the commons of both circuits are
connected, be sure that the amplifier’s 4-20 mA OUT remains unconnected and that the 4-20 mA RET (J2-8) is
connected to draw loop current from a ground referred burden resistance at the receiving circuit. The burden
resistance must not exceed 250 Ohms due to the reduced bias voltage, however a full-scale signal of -5.0 VDC is
still possible (-5V= -20 mA x 250 Ohms).
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