Inductive Coupling Situation

DOE-HDBK-1092-98

Power Cable

Tray

Pulse

Power

Supply

Load

ground

Multiconductor

Tray

I/O

Controller

ground

INDUCTIVE COUPLING SITUATION

Figure 10-6. The pulse power supply, its cable, load, and return form a transmitting loop which couples into

the loop formed by the controller, its multiconductor cabling, I/O and return. Note that in actual installations

these loops can be very large and very close.

(EMI) that may affect the cabinets. The cabinet ground remains separate from the dc signal ground

until it terminates at the master ground bus.

Eliminating grounds is not feasible for some instruments, such as thermocouples and some analyzers,

because they require a ground to obtain accurate measurements. Also, some instruments must be

grounded to ensure personnel safety.

When grounds cannot be eliminated, the solution to instrumentation ground loops lies in signal

isolators. These devices break the galvanic path (dc continuity) between all grounds while allowing

the analog signal to continue throughout the loop. An isolator also eliminates the noise of ac

continuity (common-mode voltage).2

Much of the information above came from the article which is titled "Causes and Cures of Instrumentation

Ground Loops," by Pat Power, Moore Industries, Houston, TX.

10-18