Siemens Pacemaker UM344-2 Manual de usuario descargar pdf (Pagina 45)

UM344-2 INSTALLATION

September 1995

C: Cable capacitance per unit length between one conductor and the other conductor connected to

the shield. C may be in pF/ft or pF/meter.

: Total input terminal capacitance of Field Instruments; the Primary Master is excluded. C

given by the following formula:

= (sum of all C

values) x (5000)

Where C

is an integer (e.g., 1, 2, 3) corresponding to the input terminal capacitance of a Field

Instrument. C

values are read from the following table. For Field Instruments without C

values, use C

= 1

FIELD INSTRUMENT CAPACITANCE C

VALUE

Less than 5000 pF 1

5000 pF to less than 10000 pF 2

10000 pF to less than 15000 pF 3

15000 pF to less than 20000 pF 4

20000 pF to less than 25000 pF 5

25000 pF to less than 30000 pF 6 (Model 344)

Example Calculation:

Assume a Network consists of a 344 and a Field Instrument (C

= 1 and C

= 6).

Let R = 250Ω, C = 40 pF/ft., C

= (1 + 6) x 5000 = 35,000

65,000,000 35,000 + 10,000

Then L = - = 5375 feet (1612.5 meters)

(250)(40) 40

4.3.6 Network Junctions

A Network Junction is shown in Figure 4-1. It is a wiring junction installed at a convenient point in the

loop to facilitate wiring, testing, and troubleshooting. Typically the Junction is a conventional terminal block

mounted on a panel with a protective cover, cabinet, or junction box to enclose and protect wiring

terminals.

Multiple Junctions can be installed to provide field access terminals for the connection of an MXC.

Note the following:

Ÿ Network with Barriers - Locate a Junction anywhere along the Network in the non-hazardous area

between a barrier and the Current Sense Resistor.

Ÿ Network without Barriers - A Junction may be located anywhere along the Network between the

Current Sense Resistor and Transmitter.

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Siemens Pacemaker UM344-2 Manual de usuario Pagina 45