STATUS SCIENTIFIC CONTROLS
Installation, Commissioning & Routine Gas Testing
FGD10A-M Gas Detector
TD18/032
Issue:
10
Change Note:
1869
Page 78
10.4. Broadcast Messages.
The FGD10AM will accept broadcast messages (node address 0) for the
“Write Single Register” (06H) command only. This is useful for example, in
setting the real time clock for all devices on the network, or resetting all
Latched Alarms.
The exceptions are
SPAN SENSOR
and
ZERO SENSOR
commands. For
safety reasons, each device on the network must be addressed individually
via it's Modbus node address to Zero or Span. Alternatively Zero and span
may done manually via the Menu display on the front of the instrument.
10.5. Wiring:
Use shielded twisted pair cables for connecting communication equipment
operating in accordance with MODBUS RS-485. Typical characteristics for
RS485 cable are listed below:
Cable type
Shielded cable
Conductor
resistance
(20°C)
88.0
Ω/km or less
Insulation
resistance
10000 M
Ω-km or more
Dielectric
withstand
voltage
500VDC, 1minute
Electrostatic
capacitance (1
kHz)
60nF/km or less by an average
Characteristic
impedance (100
kHz)
110±10
Ω
A termination resistor should be provided at the end of the line.
10.6. Modbus references:
A more detailed reference source is to be found at
