Siemens SIMATIC NET PROFIBUS manual Connections, Sensitivity, Power Supply, Operating Mode

Introduction

Connections

The connection between the individual nodes takes the form of an optical bus with two-fiber plastic FO cables (plastic fiber-optic cables are also known as POF, Polymer Optical Fiber) or PCF FO cables (PCF = Polymer Cladded Fiber, corresponds to HCSt 1) fiber-optic cable). Since fiber-optic cables are completely insensitive to electromagnetic disturbance, no grounding concept whatsoever is necessary. For the same reason, equipotential bonding is also not necessary. The optoelectronic conversion provides automatic isolation so that differences in potential as can occur in extensive systems have no effect.

1)HCSt is a registered trademark of Ensign-Bickford Optics

Company and stands for “Hard Polymer Cladded Silica Fiber”.

Sensitivity

Just as fiber-optic cable is insensitive to electromagnetic noise, a fiber-optic cable emits no electromagnetic noise into the environment. Sensitive electronic devices close to the fiber-optic cable therefore need no additional protection or noise suppression.

Power Supply

The OBT requires an operating power supply of 24 V direct voltage that is connected via two terminal screws.

Operating Mode

LEDs signal the current mode and any problems in operation.

Mechanical Design

The optical bus terminal consists of a compact plastic casing which can be installed either on a standard rail or on any flat surface.

1-2	PROFIBUS Optical Bus Terminal (OBT)
	C79000-G8976-C122-02