Operating instructions

AMC-DTR Sensor Transmitter User Manual
9
4.7 Alarms / RS-485 Modbus DTR-10-0234 Option Installation
Description:
The optional DTR-10-0234 Alarms/RS-485 Modbus board supplies two level alarm relays, a
FAULT relay and an RS-485 ModBus RTU slave port (Figure 7). This board is “piggybacked”
behind the DTR-10-0232 Display Assembly (Figure 5). Addition of this option requires 3-wire
mode 4-20mA operation and thereby requires the DTR-10-0233 I/O Power Supply board (Figure
6). 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 signals. 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 7: DTR-10-0234 Alarm Relays / Modbus Option
Instructions:
Unscrew the cover on the AMC-DTR 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.
RS-485 Modbus networks should be wired as shown in Figure 8. Each AMC-DTR connected
represents an RTU and must have a unique RTU address. RTU addresses are assigned in the
Modbus setup menu described in section 7.10. Cabling must be a “daisy chain” as opposed to