Operation and Maintenance - hdbk109220040183

DOE-HDBK-1092-2004

Figure 10-7. Intentional returns have been installed for both the pulse power supply and

the controller right in the trays for the cables. Both loops have been reduced to small

cross sections, reducing inductive coupling. Any electromagnetic (far field) radiation

being generated by the pulse power supply and its cabling will also be reduced.

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)3.

10.9.2.1.4 OPERATION AND MAINTENANCE

Before starting each operation (experiment, test, etc.) the exposed portions of the grounding

system should be visually checked for any damage and to determine that all necessary

connections have been made. If more than one operation is conducted every day, then visual

checks should be performed only at the beginning of each shift, if the grounding system will be

needed during that shift. The adequacy of the grounding system should be verified annually. It is

recommended that the grounding impedance within the equipment be maintained at 0.25 ohms or

less. (See IEEE 1100).

Much of the information above came from the article entitled Causes and Cures of Instrumentation Ground

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

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