Siemens SIMATIC NET PROFIBUS User Manual

7-1

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

Table 7-1

 Technical Specifications

Technical Specifications

Power supply (safety extra–low voltage with reliable
isolation, SELV or complying with NEC Class 2)

24 VDC   (18 V to 32 V)

Power consumption at 24 V input

max. 200 mA

Transmission rate

12 Mbps, 6 Mbps, 3 Mbps, 1.5 Mbps, 500 Kbps, 187.5
Kbps , 93.75 Kbps, 45.45 Kbps, 19.2 Kbps, 9.6 Kbps

Transmission rate setting

made automatically

Mode

optical bus

Bit error rate

<10

–9

Input channel 1 to channel 3

Bit length
Jitter

0.7 to 1.3 tBit
-0.03 to +0.03 tBit

Output channel 1 to 3

Bit length
Jitter

0.99 to 1.01 tBit
-0.003 to +0.003 tBit

Signal delay time (any input/output)

≤

 6 tBit

Cascading depth of optical bus

limited only by signal run time

Electrical channel

Input/output signal

RS–485 level

Input dielectric strength

-7 V to +12 V

Minimum current at 5V (for terminating resistors)

10 mA

Electrical isolation from 24V input

Isolation due to function; not safety–related!

Optical channels

Optical source

LED

Coupled optical power

– in plastic fiber 980/1000 
– in PCF fiber 200/230

   P

T(min)

                  P

T(max)

– 5.9 dBm                +0.5 dBm
– 16 dBm                –1.5 dBm

Receiver sensitivity

– with plastic fiber 980/1000
– with PCF fiber 200/230

   P

R(min)

                  P

R(max)

–20 dBm                     0 dBm
–22 dBm                   –2 dBm