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Typical 4-20 mA Loop
Notes:
- Loop impedance must be considered,
to prevent overloading the power supply.
- If any one instrument is disconnected,
the complete control loop will fail to operate
- 20 AWG shielded twisted pair cable
is recommended. The twisted pair configuration tends to
distribute any electrical noise in a common mode; it is
on both wires and tends to cancel itself out.
- Wiring needs to be run away form sources
of EMI, such as 120V or larger power lines or equipment
that generates EMI.
- When using a shield, some simple rules
apply:
- A shield should be grounded on one
end only by using the green wire from the power source
and not the negative (-) lead of the sensor connector
or the negative (-) of any of the power supplies.
- Think of the shield as a flexible
conduit in the wiring scheme and remember that metal conduits
are always at earth ground. Attach it to ground at one
end only to prevent it from becoming a conductor and creating
a ground hazard.
- The recommended point of grounding
is at the instrument, since it is difficult finding a
good ground near a D/P or next to an Electronic Sensor
Control Box.
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