Cable Shielding and Grounding in Accelerometers

Most vibration sensors (accelerometers) are contained within a stainless steel housing that is electrically isolated from the internal sensing element. The sensor housing is typically grounded to the machine frame, which is in turn connected to the facility's structural ground.

Connecting the cable shield at both ends (the sensor end and the measurement instrument end) can create a "ground loop." Ground loops occur when there is a potential difference between the ground points of the sensor and the instrument, causing unwanted current to flow through the shield. This current can induce significant noise (interference) into the vibration signal.

<div class="wp-block-image"><figure class="aligncenter size-full"><img src="https://ads-teknisyen.com/wp-content/uploads/2022/11/Ekranli-Kablo-Semasi.png" alt="Cable Shielding Diagram" class="wp-image-2146"/></figure></div>

To prevent ground loops and provide effective electromagnetic interference (EMI) protection, specific shielding protocols must be followed:

<ol> <li><strong>Shielding at the Sensor End:</strong> In standard applications, the cable shield should be cut back and isolated at the sensor end. It must not be connected to the sensor housing or the machine ground.</li> <li><strong>Shielding at the Instrument End:</strong> The shield should be connected to the "Shield" or "Common" terminal at the signal conditioner, data logger, or PLC/BMS side. This ensures that any noise picked up by the shield is drained to a single reference ground.</li> <li><strong>Cable Routing:</strong> Sensor cables should be routed away from high-voltage power lines, frequency inverters (VFDs), and large electric motors to minimize inductive coupling.</li> </ol>

For sensors used in hazardous areas (ATEX/IECEx), specialized grounding requirements may apply. In such cases, the guidelines provided by Hansford Sensors or MTL regarding galvanic isolators and Zener barriers must be strictly followed to ensure intrinsic safety.

Proper shielding is critical for maintaining signal integrity, especially when monitoring high-frequency vibrations or when using long cable runs in industrial environments. Without correct grounding, the data from the accelerometer may be distorted, leading to false alarms or missed machine faults.