Siemens sitrans LR 400 Instruction Manual page 104

Bus Termination
PROFIBUS PA MUST be terminated at both extreme ends of the cable to
Note:
work properly. Please refer to the PROFIBUS PA User and Installation Guidelines
(order number 2.092), available from www.profibus.com.
Power Demands
To determine how many devices can be connected to a bus line, calculate the
combined maximum current consumption of all the connected devices: 10.5 mA for
SITRANS LR 400. Allow a current reserve for safety
Cyclic versus Acyclic Data
When you request data from a device via PROFIBUS PA, you have two choices. Cyclic
data is provided at every bus scan: acyclic data is requested and provided as needed.
Input and output information is always requested at every bus scan and is set up as cyclic
data. Configuration information is only needed periodically and is set up as acyclic data.
Cyclic Data
When you configure SITRANS LR 400 on the PROFIBUS PA bus, there are two slots
available for modules.
Each of the slots has to have a module defined in it.
Note:
Slot 0 always transmits Level information and slot 1always Volume information. Slot2 is
always Mass information. If you do not wish to have data transmitted, then you must use
a Free Place module in that slot.
When you select a module, for the three values, there are two alternatives: a normal
version and a short version, for example, Level (short) and Level. The difference between
the two is the way each one identifies the function block used. Level uses both the
identifier and the extended identifier byte to determine which function block in the unit to
use. Level (short) uses only the identifier byte. In the current release of PROFIBUS PA
there is no functional difference between the short and normal versions. However, the
longer identifier is the preferred way to identify the function block.
The 3 function blocks (Level, Volume, Mass) return 5 bytes of data each:
Level byte 1
Volume
byte 6
Mass byte 11
7ML19985JC02 SITRANS LR 400 (Solids) – INSTRUCTION MANUAL
Floating Point
byte 2 byte 3
byte 7 byte 8
byte 12 byte 13
Status
byte 4 byte 5
byte 9 byte10 byte10
byte 14 byte 15
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