Published: 2025-08-12 09:18:17
The encoder cable shielding layer requires grounding at both ends, mainly to maximize shielding effects, reduce the impact of electromagnetic interference (EMI) and radio frequency interference (RFI) on signal transmission, and ensure the stability and accuracy of encoder signals. The specific reasons are as follows:
1. Forms a complete shielded loop to block interference coupling paths
Encoder operating environments typically contain numerous sources of electromagnetic interference (such as motors, frequency converters, relays, etc.), which generate alternating electromagnetic fields that can easily interfere with signals inside cables through "capacitive coupling" or "electromagnetic induction."
The shielding layer is essentially a conductive metal layer (such as copper mesh or aluminum foil). If only one end is grounded, a "suspended" conductor forms between the shield and the grounded terminal, similar to an antenna, which may instead receive external interference and conduct it through capacitive coupling to the internal signal line.
When both ends are grounded, the shielding layer forms a closed circuit with the grounding bodies at both ends (such as equipment casings and grounding busbars). The interference current induced by external electromagnetic fields on the shielding layer can be directly discharged through the grounding circuit, preventing interference from "transferring" to the internal signal layer.
2. Suppress interference caused by 'earth potential difference'
In industrial sites, the grounding terminals of different equipment may have slight 'ground potential differences' (caused by differences in equipment power, grounding resistance, etc.). If the devices connected to both ends of the encoder cable (such as the encoder itself and the PLC or driver) are at different ground potentials, a weak current will be generated.
If the shielding layer is grounded at only one end, the current generated by the ground potential difference may couple through the capacitance between the signal line and the shielding layer, interfering with signal transmission (manifested as signal fluctuation and errors).
When both ends are grounded, the shielding layer can act as an 'equipotential connector,' directing the potential difference between the two ends to the shielding layer's own low-impedance path, thereby reducing the impact of interference currents on internal signal lines.
3. Improve shielding effectiveness against low-frequency interference
Interference signals can be divided into high frequency and low frequency according to frequency:
High-frequency interference (such as radio frequency signals) can be shielded through a single-ended grounded shielding layer, using 'reflection loss' and 'absorption loss' for shielding;
Low-frequency interference (such as the common 50Hz power frequency interference and motor commutation interference in industrial environments) relies more on the 'short-circuit' effect of the shielding layer — a closed loop formed by grounding both ends can 'short-circuit' the induced currents generated by low-frequency alternating magnetic fields, significantly reducing their induced interference on internal signals. Encoder signals are often low-frequency pulses or analog signals (such as A/B phase pulses of incremental encoders), which are more sensitive to low-frequency interference, and therefore require grounding at both ends to reinforce the shielding.
Precautions
Although grounding at both ends has significant advantages, the "grounding loop" problem must be avoided: if the shielding layer grounded at both ends forms a closed loop with the equipment's grounding system, electromagnetic induction inside the loop may cause circulating current, which may interfere with the signal. Therefore, in practical applications, it is necessary to ensure the "equipotential" of grounding at both ends (such as unified grounding via a grounding bus), or when grounding resistance differs significantly, adopt a compromise where one end is directly grounded and the other end is grounded via capacitor (high-frequency grounding), balancing shielding effect and loop interference prevention.
In short, grounding both ends of the encoder cable shielding is a key measure to ensure signal transmission stability in industrial environments, with the main purpose being to maximize the isolation of internal and external interference through a complete shielding loop and equipotential connection.