Rockwell Automation Publication 1443-TD001D-EN-P - March 2019
9
1443 Series Accelerometers Specifications
EMI
Ground the shield at both ends of the cable.
• If you tie the shield to the sensor case only, it creates a ground if the structure that the sensor is mounted on is
grounded. If the bearing housing or the machine is isolated from ground, then when you connect the shield to the
case of the sensor cannot ground the shield.
• If the ground potential through the sensor is different than ground potential through the instrumentation ground,
then a ground loop is created. The ground loop that is created can be a worse condition than the EMI problem.
• In most cases, grounding the shield at both ends must be the last resort because ground loop problems can result.
The ground loop problems can create more significant problems than the EMI issue. Make sure that the following
common wiring solutions are considered:
– Use high quality, well shielded, twisted wire cable.
– Route cable runs to avoid obvious / strong sources of EMI such as radio transmission towers, generators,
and transformers.
– If cables are routed through a J-box, make sure that shields are properly connected.
– When routing cables, make sure to cross AC power lines at right angles. Approach AC motors from a right
angle to the motor shaft and do not route wiring alongside a motor.
– At the monitor, connect the shield wires directly to ground - so do not ground it through the instrument.
Ground Loops
Isolate the shield at one end of the cable.
• In most cases, make sure that the shield is not connected to the sensor.
• A special cable or a custom made cable is required for accelerometers with two or three pin
MIL-C-5015 connectors.
• For existing installations, do not assume that the shield is not tied to the sensor case. While not connected to the
sensor case is normal practice in most locations, it doesn't mean that it is that way. Also, if the shield is connected to
the sensor case, it’s possible that the structure the sensor is mounted on has changed in respect to the ground for
other reasons.
• If continuous or intermittent EMI (RFI) sources are present, then when you isolate one end of the shield it creates
an antenna that can result in EMI (RFI) noise problems. An EMI (RFI) issue can be a worse condition than the
ground loop problem.
