How does shielded cable help in HART installations?

How does shielded cable help in HART installations?

• A. It increases the loop current capacity
• B. It provides mechanical protection only
• C. It has no impact on data integrity
• D. It reduces EMI and noise coupling into the low-level digital signals on the current loop, improving data integrity

Answer: (D)

Shielding reduces EMI affecting the digital data on the current loop. In a HART system, the digital information rides on top of the 4–20 mA analog signal, so the small, high-frequency changes that encode data are vulnerable to external noise and electromagnetic interference. A shield around the cable provides a low-impedance path to ground for interfering signals, keeping them from coupling into the conductors and distorting the digital transitions. This directly improves data integrity because the guarded channel carries the low-level digital information more cleanly. It doesn’t increase loop current capacity or serve mainly as mechanical protection, and it does have a meaningful impact on data integrity when properly implemented. For best results, ground the shield at one end and keep the shield continuous along the run to maintain effective shielding.

Shielding reduces EMI affecting the digital data on the current loop. In a HART system, the digital information rides on top of the 4–20 mA analog signal, so the small, high-frequency changes that encode data are vulnerable to external noise and electromagnetic interference. A shield around the cable provides a low-impedance path to ground for interfering signals, keeping them from coupling into the conductors and distorting the digital transitions. This directly improves data integrity because the guarded channel carries the low-level digital information more cleanly. It doesn’t increase loop current capacity or serve mainly as mechanical protection, and it does have a meaningful impact on data integrity when properly implemented. For best results, ground the shield at one end and keep the shield continuous along the run to maintain effective shielding.