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Pag. 35
³ Detector power supply (and IN and OUT modules on the bus) must be connected with
a 2- core wire with adequate section based on the number of connected devices, their
distance from the power supply and each device’s consumption (please see the tech-
nical manual enclosed with gas detectors for this purpose).
Each device connected on the unit’s RS485 bus must have its own univocal address. See the
appropriate section of this manual to set the address of the STG/IN8S and STG/OUT16S mo-
dules and see the relative manual for setting the detector address.
2.8 Detector connection
Gas detectors can be connected to the PL4 +D gas control unit in two dierent ways, based
on the detector output signal.
1. 4-20 mA analogue proportional output
The detector connected to the unit and STG/IN8S module will send a 4-20 mA signal refer-
ring to its range (i.e. 0-300 ppm, 0-30 ppm, 0-100% LFL etc.) and the unit, suitably program-
med, will display the relevant gas concentration indication measured by the detector and
consequently activate the alarms when the set values are reached.
2. RS485 digital proportional output
The detector connected to the gas control unit will send a data signal on the RS485 line. This
signal refers to the range of the detector (i.e. 0-300 ppm, 0-30 ppm, etc.); the unit, suitably
programmed, will display the relevant gas concentration indication measured by the detec-
tor and consequently activate the alarms when the set values are reached.
Detectors with 4-20mA output
Detectors with 4-20mA analogue output are either connected to the gas control unit, direct-
ly on the main board or via one remote 8-input STG/IN8S module. The module may be con-
nected remotely to the gas control unit. For connection, a detector with a 4-20mA analogue
output requires a 3-conductor cable: two conductors for the power supply (usually from 12
to 28 Vdc - refer to the gas detector technical manual) and one conductor for the 4-20mA si-
gnal. The generally recommended cable is a shielded 3 x 0.75, which allows up to 100 meters
between the gas detector and STG/IN8S input module.
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