RKI Instruments M2 for 12 VDC - Manual (Page 10)

5 M2 Transmitter Operator’s Manual, 12 V DC Operation
Terminal PCB
The terminal PCB is encapsulated in epoxy for protection against moisture and physical
damage. It is mounted into the rear of the junction box with three standoffs and rests on a
thin layer of foam. A banana jack is screwed into each of the standoffs and used for
mounting the control PCB. The terminal PCB converts the electrical output from the
detector to a signal which can be displayed by the LCD display, a 4 - 20 mA signal (that is
proportional to the detection range) and an RS-485 Modbus output signal. The 4 - 20 mA
signal may be used by a recording device, gas monitor controller, or programmable
controller. The Modbus output may be used to connect the M2 to a Modbus network. The
terminal PCB also controls three relays, one fail and two gas alarm relays.
Two columns of plug-in style terminal strips are used to make all wiring connections to
the M2. The column on the left consists of the power/signal, detector, and Modbus
terminal strips. The column on the right consists of the relay terminal strips. A 20 position
connector at the bottom of the terminal PCB is used to connect the terminal PCB to the
control PCB with a ribbon cable. A 5 position connector on the left side of the terminal
PCB is used by factory or field service personnel to program the M2. A factory adjust pot
just above the programming connector is used to set the LEL detector current.
Power/Signal Terminal Strip
The power/signal terminal strip is a three position plug-in style terminal strip located at
the top of the left terminal column. It is used to connect 12 VDC power to the M2 and to
connect the 4 - 20 mA output signal to a device.
The signal output, the S terminal, does not have to be connected for the M2 to function.
The S terminal is used if you want to connect the 4 - 20 mA output signal to another device
such as a gas monitoring controller, chart recorder, or programmable controller (PLC).
Detector Terminal Strip
The detector terminal strip is a four position plug-in style terminal strip and is the middle
terminal strip in the left terminal column. It is used to connect the LEL detector to the M2.
NOTE: The LEL detector is factory-wired to the M2. See “Wiring the M2 Transmitter”
on page 9 for all wiring procedures related to M2.
Modbus Terminal Strip
The Modbus terminal strip is a three position plug-in style terminal strip and is the
bottom terminal strip in the left terminal column. It allows connection of the M2 into a
Modbus network.
Relay Terminal Strips
The right column of terminal strips consists of, from top to bottom, the fail, alarm 1, and
alarm 2 relay terminal strips. They are three-position plug-in style terminal strips. The
relay terminal strips are used to connect devices such as lights and horns that are
controlled by the relay contacts. The relay contacts are rated at 115 VAC, 5 amps. The relay
contacts may also be used to control higher rated relays.
Termination Jumper
A two pin header with a termination jumper installed is located below the Modbus
terminal strip. The jumper has no function unless the M2 is wired into a Modbus
installation. See “Chapter 8: RS-485 Modbus Output” on page 29 for a description of using
the M2 in a Modbus system.