Sensitron PL4 +D - 2.3 JP27 Connector Function; 2.4 Field Device and Detector Connections

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2.6 JP27 connector
If the JP27 connector is closed, the line terminator is enabled. It’s important to maintain
always this conguration.
Figure 9) Always keep JP27 closed
2.7 Field device connections
The gas control unit has one RS485 data bus to which 8 gas detectors can be connected. The
gas detectors are connected through the serial bus (directly in the serial RS485 if equipped
with serial output or through one module with 8 STG/IN8S inputs if of type 4-20 mA) and the
STG/OUT16S output module. The maximum length of each serial data bus is 800 m.
To connect devices, four conductors are required (intended both as detectors with a serial
output as well as IN and OUT modules): two for the RS485 serial bus and two for powering
the devices. For this reason, two dierent wires must be used or a single wire that has sui-
table characteristics, as described below.
³ The RS485 serial bus must be connected with an EIA RS 485 connection wire: No. 2 wi-
res with 0.22/0.35 mm2 section with shield (TWISTED PAIR). Nominal capacity between
conductors < 50 pF/m, nominal impedance 120 ohm. Total line length with this type
of connection must not exceed 1,000 metres. An example of a recommended cable is
a BELDEN 9841 or similar wire (EIA RS485 data transmission wire). Only connect detec-
tors (and IN and OUT modules) in a “cascading” manner. Avoid tree or star connections
since they reduce interference immunity.