Siemens SIMATIC NET PROFIBUS Manuale Utente

2-18

PROFIBUS Networks SIMATIC NET

6GK1970-5CA20-0AA1 Release 2 05/2000

PROFIBUS-DP

PROFIBUS-PA

I

max

I

1

I

2

I

3...

...I

m

I

max

 

x

 400 mA

24 V DC

Field device

1

Field device

2

Field device

3...

Field device

...m

PROFIBUS-DP

PROFIBUS-PA

I

max

I

1

I

2

I

3...

...I

n

I

max

 

x

 90 mA

24 V DC

Explosion-protected area

Field device

1

Field device

2

Field device

3...

Field device

...n

Protection EEx [ia] II C

I

max

 

x

 110 mA

Protection EEx [ib] II C

Figure 2-12

Field Device Power Supply in the Hazardous and Non-Hazardous Area

If the maximum output current of the DP/PA coupler is exceeded, you must include
a further DP/PA coupler.

The total cable is the total of the main cable and all the tap lines.

When using a standard PROFIBUS-PA cable with a cross-sectional area of
0.8 mm

2

, the maximum length of the total cable (with a maximum number of field

devices and worst-case positioning at the end of the cable) is as follows:

S

560 m for DP/PA coupler (6ES7 157-0AC00-0XA0)

S

680 m for DP/PA coupler (6ES7 157-0AD80-0XA0)

S

790 m for DP/PA coupler Ex [i] (6ES7 157-0AD00-0XA0)

The maximum permitted tap line lengths are listed in Table 2-2. You should also
remember the maximum length of the total cable (see above).