Black Box IC108A Betriebsanweisung PDF herunterladen (Seite 34)

Advant

Smart Device (HART

) Interface User’s Guide

Chapter 2 Installation

2-22 3BUR 001 085R0001 REV A

can be set on the 8-position DIP switch labeled S2 which is accessible from the back panel of

the SHIM’s housing as shown in Figure 2-16.

The first and second switch positions (S2-1 and S2-2) are set to OFF, indicating parity of None.

The third through fifth switch positions (S2-3 through S2-5) are respectively set to ON, OFF,

and ON, indicating a baud rate of 9600. Switch positions S2-6 through S2-8 are always set to

OFF. Table 2-13 lists the switch position S2-1 through S2-5 settings and the parity and baud rate

they set.

2.3.1.5 Smart Device Connections

As indicated in Table 2-11, there are three contacts on SHIM terminal blocks XTB2 and XTB3

for each of the up to eight smart devices you can connect to a SHIM: Excitation, Signal+, and

Signal-. Excitation connections are protected by a shared 0.5 Amp Excitation fuse located on

the front panel, but there is no current limiting resistor or fuse per Excitation connection.

Therefore, if a SHIM powers a smart device loop, an external 50 mA fuse is required on the

corresponding SHIM Excitation to smart device Tx+ wire. Otherwise, a blown Excitation fuse

takes down all smart device loops powered by the SHIM without affecting serial communication

with the SHIM. Digital communication from smart devices is AC coupled to the SHIM on

corresponding Signal+ connections, and all Signal- connections to the SHIM are internally

shorted together to COM.

The physical connection between the screw terminations of a smart device and a SHIM is made

using a cable referred to as a HART Bus. See Section 5.4.1.2, Smart Device Removal and

Installation Procedures for specific installation and removal information.

NOTE

The maximum length of the HART Bus is 10,000 ft. (3,048 m) or is determined

using the following formula, whichever is less:

L = 65,000,000 / (R x C) - (C

+ 10,000) / C

where L is the length in feet or meters, R is the total loop resistance in ohms, C is

the cable capacitance in pF/ft. or pF/m, and C

is the sum of CN values of smart

Table 2-13. DIP Switch Position S2-1 Through S2-5 Settings

and Their Corresponding Parity and Baud Rates

Parity S2-1 S2-2 Baud Rate S2-3 S2-4 S2-5

None OFF OFF 300 OFF OFF OFF

Odd OFF ON 600 ON OFF OFF

Even ON OFF 1200 OFF ON OFF

Reserved ON ON 2400 ON ON OFF

4800 OFF OFF ON

9600 ON OFF ON

19200 OFF ON ON

Reserved ON ON ON

1 2 ... 29 30 31 32 33 34 35 36 37 38 39 ... 117 118

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