2-72 rnsfa//afion
2.11
Ground Loops and Common Mode
Voltage
Ground loops occur when either the return wire or the sensor is
grounded at the process line and Jumper 5 on the mounting cassette
is intact. To correct this situation, the input should be connected as a
differential input (Jumper 5 cut). The input then floats with respect to
supply ground. The maximum common mode voltage (CMV) the
controller should receive when wired in this manner is -5 to +I7 volts
taken from the input negative pole to supply ground. If these limits are
expected to be exceeded, an isolation amplifier must be used.
For each of the points 1 thru 4 in the following
example, the table lists the maximum potentials
and grounding possibilities.
4 - 20mA
SeWDr
I
CMV referred
to this point
UM6.1:DPF?900:9147
Change 2 -July 1992
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