Crowcon Crowcon Gasmaster, Инструкция по установке, эксплуатации и обслуживанию, Страница: 17 / 48

Crowcon Gasmaster Installation
13
input signal. If the ‘pellistor saver’ function is
enabled, at 95%LEL (this value is adjustable) gas
concentration the channel will enter ‘pellistor
saver’ mode (refer to section 3.9); the channel will
go into fault and the analogue output signal will
be set to 0mA.
If the ‘pellistor saver’ function is disabled the ana-
logue output will rise to a maximum of 25.8mA;
the %LEL indication will depend on the gain levels
set for the sensor.
Figure 2.18
OUTPUT
1
SCR
0V
SIG
OUTPUT
2
SCR
0V
SIG
OUTPUT
3
SCR
0V
SIG
OUTPUT
4
SCR
0V
SIG
Link: 1-5V
No Link: 4-20mA
Link: 1-5V
No Link: 4-20mA
Link: 1-5V
No Link: 4-20mA
Link: 1-5V
No Link: 4-20mA
Gasmaster analogue output connection
terminals
2.9.5. RS-485 communications
Gasmaster can provide alarm and system informa-
tion to PLC/DCS/SCADA systems via a two-wire
link using the Modbus RTU protocol (9600 baud,
8 data bits, no parity, 1 or 2 stop bits). Up to 16
Gasmaster systems can be 'multi-dropped' on
a single two-wire link with a maximum cable
length of 1 Km, two-core twisted pair cable is
recommended. Single Gasmaster systems that
are to communicate via the RS-485 link should
have the
RS485 TERM
link made, which connects
a terminating resistor. For multi-dropped systems
the
RS485 TERM link should be removed from all
Gasmasters except the last unit on the line.
A Modbus specification document is available
from Crowcon on request.
The RS-485 terminals on Gasmaster systems
ordered with the optional local communications
connector will be used for terminating the con-
nector leads. These leads must be removed if a
remote RS-485 serial link is required.
Figure 2.19
485A
485B
SCR
J
14
LK2
RS485
TERM
Gasmaster RS-485 terminals
2.10 Applying power
Before applying power ensure that any
control or shutdown systems to which the
Gasmaster is connected are inhibited.
Once all field cables have been installed, the
batteries can be connected as per the diagram
attached to the chassis plate. (Refer to section
4.4.) Gasmaster will not power up until an exter-
nal power supply is applied.
Apply power to Gasmaster from either the AC or
24 V dc external supplies. Outputs are inhibited
for a preset time after power-up, and the system
will perform a start up sequence testing alarm
indicators and the internal sounder. If after a set-
tling period faults are reported, check the sensor
connections again or refer to "Faults menu (lists
faults present on the system)" on page 24.
When power is applied the green Power LED will
illuminate and flash every 5 seconds to indicate
that the system is operational.
If the external supply fails, Gasmaster will con-
tinue to operate from its internal batteries and
the Power LED will flash every second. Depending
on configuration, Gasmaster will display either a
Warning (Warning LED lights and the sounder will
beep every 5 seconds) or a fault (the Fault LED
and sounder will activate, and the fault relay will
change state).
Gasmaster should display all channels being
monitored. Allow sensors to settle before com-
mencing calibration, refer to sensor instructions
supplied with detectors for recommended settling
times.
Note: your Gasmaster is supplied pre-config-
ured, refer to the Specification and Inspection
Certificate provided with your system. If no chan-
nels are configured, Gasmaster will display the
following screen: