Optical Isolation; Plant Ground - Baldor 29M Installation And Operating Manual

Section 1
General Information

Optical Isolation

Optical Couplers
Fiber Optics

Plant Ground

5-18 Troubleshooting
Two methods of optical isolation are commonly used; optical couplers and fiber optics.
The common term for optical couplers, opto couplers use a light transmitter and light
receiver in the same unit to transmit data while electrically isolating two circuits. This
isolation rejects some noise. The magnitude of noise rejection is usually specified by the
"common mode rejection, dv/dt rating". Typically, low cost opto couplers have a common
mode rejection of 100 to 500 V/ sec, which is adequate for most control logic signals.
High performance opto couplers with common mode ratings up to 5,000 V/ sec are
installed for the most severe noise environments.
Special plastic or glass fiber stands transmit light over long as well as short distances.
Because the fibers are immune to electromagnetic energy, the use of fiber optic bundles
eliminate the problem of coupling noise into such circuits. These noise–free fiber optic
cables can be run with power or motor conductors because noise cannot be inductively or
capacitively coupled into the fiber optic strands.
Connecting electrical equipment to a good ground is essential for safety and reliable
operation. In many cases, what is perceived as a ground is not ground. Result:
equipment malfunctions or electrical shock hazard exists.
It may be necessary to retain the services of an electrical consultant, who is also a
licensed professional engineer experienced in grounding practices to make the necessary
measurements to establish if the plant ground is really grounded.
MN1230