Installation, Operation & Maintenance Manual Merlin Gas Detector-X
DETX-IOM Iss: 7 02-21
7
MODBUS
Connection
A shielded and twisted 2 or 4 core cable is used to wire the data terminals [D+ & D-).
Any cable with similar characteristics can be used to connect all the devices together.
The shielding can be of 2 types: braided [mesh of thin conducting wires]
or foil (consisting of a thin sheet of metal covering the twisted wires).
One example of such cable is BELDEN 3082A.
If you are encountering noise or irregular problems with a bus link, the problem is likely related to
grounding, incorrect shielding or wiring mains power next to Modbus wiring.
To ground the data cable, the shield should be connected to ‘Power’ [-] terminals!
Creating a Detector Chain
Create a detector chain by connecting detectors in a parallel (daisy chain) method.
Any other way may cause issues or damage to the overall system.
**Single chain example.
**Split chain example
Reversing the [D+] and [D-] connections of any device can lead to the whole system to stop working
owing to reverse polarity found on the terminals. In order to avoid this problem, it is recommended that
the cable of same colour should be used to connect all [D+] terminals together and similarly cable of same
colour to be used to connect all [D-] terminals together.
**Where connections may exceed 100 metres from one control panel – Contact your supplier!
