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Installation, Operation & Maintenance Manual
Installation Tips
Wiring detector chains
The best way to connect devices in a MODBUS RTU communication is a parallel DAISY CHAIN method.
Cable distance
You may encounter problems when powering detectors beyond 100 yards from one control panel, in this instance,
contact your supplier.
Resistance to interference
Signal communication issues may occur where the bus length is too long, high baud rates are used or signal
reflections are occurring. To avoid this, terminating at each end of a chain may help the quality of the data signal by
turning on the 120ohm terminal resistor switch of the first and last device in the chain.
Earthing/Grounding
If you are encountering noise or irregular or abnormal problems, the problem is likely related to grounding, incorrect
shielding or wiring mains power cables next to data cables. If using a shielded cable – ensure the shielding or
equivalent is wired to the [Shield Wire] terminal on the detectors and connected to a mains powered earth/ground
point on the control panel.
Cable characteristics
For MODBUS communications, a shielded and twisted pair cable is used. The shielding can be of 2 types: braided
[like a mesh of thin conducting wires] or like a foil [consisting of a thin sheet of metal covering the twisted wires].
Detector protection
High concentrations of alcohol found in many products may damage, deteriorate or affect the gas sensing elements of
the detectors – such as; wine; deodorants; stain removers; thinners etc.
Detector identification
Remember to individually ID each connected detector by configuring the ID switches on the circuit board. Make a
plan, map and/or note of the location of all connected detectors for tracing and locality purposes.
Buzzer on alarm
There are no provisions to silence the alarm buzzer when high gas levels are detected. Gas levels must return to safe
level for the buzzer to stop. The audible buzzer is optional via a switch on the circuit board.
Operation
Initial Power-Up (Commissioning)
On connecting power, the detector enters 'sensor stabilisation' phase for approximately 60 seconds – during this
period the screen will display an 'initialisation' message indicating that the device is not yet ready for gas detection.
After the sensor has stabilised – the screen will display;
a.
Target gas.
b.
Target gas value.
c.
Target gas measurement (parts per million or % LEL).
d.
Unique detector serial/batch number.
e.
Configured ID number.
We recommend all gas detection systems be commissioned by a competent/trained engineer to ensure
correct installation and operation!
IOM Iss: 4 11-21
Merlin Detector-TFT
9
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