Oldham OLCT 200, User Manual, Page: 25 / 80

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OLCT 200 User Manual | 25
2.7 Alarms / RS-485 Modbus 10-0234 Option Installation
Description:
The optional 10-0234 Alarms/RS-485 Modbus board supplies two level alarm relays, a
FAULT relay and an RS-485 Modbus RTU slave port (Figure 2-10). This board is
“piggybacked” behind the 10-0232 Display Assembly (Figure 2-3). Addition of this
option requires 3-wire mode 4-20mA operation and thereby requires the 10-0233 I/O
Power Supply board (Figure 2-5). This is since relays and RS-485 circuits require
much more power than 2-wire 4-20mA loops can deliver.
CAUTION:
Alarm relays have dry contacts and power must be supplied from an
external source. Contacts are rated for RESISTIVE loads! Inductive loads, such as
contactor coils or motors, may cause contact arcing, which shortens life and emits RFI
into the sensor sign
als. Use appropriate arcing snubbers and MOV’s across inductive
loads and keep wiring away from signal wires. External wiring to TB3 (Remote Alarm
Reset) should be shielded and protected from noise spikes to prevent false Alarm
Reset.
Figure 2-10: 10-0234 Alarm Relays / Modbus Option
Instructions:
Unscrew the cover on the OLCT 200 explosion-proof enclosure. Loosen the two
thumbscrews holding the display assembly in place and remove it. A small ribbon
cable is attached with sufficient length to access the back of the Display assembly
where the Alarms/RS-485 Modbus board option is located. It is possible to use only
the relays, only RS-485, or use both. Relay terminals are labeled NO (normally open),
NC (normally closed) and C (common or the pole). These designators correspond to
the shelf, or de-energized, state of the relays. The FAULT relay is always failsafe,
meaning it is energized when there is not a fault condition and therefore its action is
reverse of the designators.
7
TB2
TB1
TB3
K2
K3
K1
Remote Alarm Reset
ST-48 Alarm / ModBus Option
Assy: 10-0234
1
C
NC
NO
C
NC
NO
C
NC
Relay 1
(K1)
Relay 2
(K2)
Relay 3
(K3)
2
3
4
5
6
8
9
NO
1
2
3
4
5
P1
J1
U1
A (Installs RS-485 Terminating Resistor)
B (Omits RS-485 Terminating Resistor)
A
B
S
A
B
1
RS-485
‘A’ & ‘B’ terminals are
connected internally for easier
IN / OUT cabling.
‘S’ is “no connect” for shield
to continue.