GASMAX II + GDS-IR Operation & Maintenance Manual, Revision 1.1
Page 12
OPTIONAL RELAY + MODBUS INTERFACE
The optional 10-0234 Relay / Modbus board is
connected “piggyback”
to the back of the GASMAX II
Display Assembly and supplies two level alarm relays
(“K ” and “K ”)
, a FAULT relay
(“K3”)
and an RS-485
Modbus RTU slave port. If dual isolated 4-20mA outputs are
not
installed, GASMAX II units may be field
upgraded with this option at any time.
RELAY FUNCTIONALITY
Alarm relays
are dry contact P and may be configured as normal or failsafe (“normally open h
eld
closed”).
Power must be supplied from an external source and should be fused.
WARNING:
CONTACTS ARE RATED FOR RESISTIVE LOADS ONLY! INDUCTIVE LOADS, SUCH AS COILS,
MOTORS OR SOLENOID VALVES MAY CAUSE ARCING WHICH SHORTENS LIFE AND MAY INTERFERE WITH
SENSOR DATA. IF OPERATING AN INDUCTIVE LOAD, BE SURE TO INSTALL A PROTECTIVE DIODE OR
‘ BBE ’
AT THE LOAD PINS
TO MINIMIZE REVERSE EMF ARCING.
Relay K1 activates if either Channel 1 or Channel 2 exceed the programmed alarm 1 threshold and cannot
be acknowledged. Relay K2 activates if either Channel 1 or Channel 2 exceed the programmed alarm 2
threshold and can be acknowledged (reset) from the front panel or via TB3. Relay K3 indicates sensor
failure and is always failsafe (normally open held closed).
Remote Alarm Reset
(TB3) can be used to acknowledge an Alarm 2 relay contact closure via a remote
pushbutton. Use a momentary dry-contact normally-
open switch between “+” and “
-
“ to force a reset.
Wiring from any remote pushbutton to TB3 should be shielded and protected from noise spikes to
prevent false Alarm Reset commands.
A version of this board is available with MODBUS RTU slave only configuration (No relays).
Figure 3-2: Optional Relay / MODBUS Interface Board
MODBUS WIRING
Typical MODBUS wiring is shown in Figure 4-6. MODBUS system architecture requires that the devices in
any MODBUS loop be connected in a daisy-chain layout. This minimizes signal reflections and improves
K
K
K3
3
6
3
B
B
B
K
B
B3
C
C
O
C
C
O
C
C
O
K
K3
MO B / elay
-
3
MO B ermina on umper
“ ” installs umper
“B” omits umper
-
+
