Manual

M2 Transmitter Operator’s Manual 10
Internal Description
This section describes the internal components of the M2. The internal components of the
M2 include the terminal PCB which provides for all the wiring connections to the M2 and
the control PCB which displays the gas reading and has the control buttons.
Figure 9: M2 Internal Components
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
UP/YES
C NC NO
PW R/SIG
ALARM 1
FAIL - S +
LEL
- S +
PW R/SIG
RS 485
ALARM 2
A B C
RS 485
A B C
DOWN/NO
ENTER
Modbus
Terminal Strip
C N C N O
RKI INSTRUMENTS
M2 TRANSMITTER
LE L
C NC NO
R W G B
R W G B
LCD Display
Push Button
Control
Switches
ENTER
DOWN/NO
UP/YES
Terminal PCB
Control PCB
TX LED
RX LED
Alarm 2 LED
Alarm 1 LED
Fail LED
View With Cover and
Control PCB Removed
Magnetic
Switches
Junction Box
View With Cover Removed
Detector Current Pot
(Comb/CO2 T ype
Only, Factory Adjust)
Display Ribbon
Cable Connector
Termination Jumper
Programming
Connector
(Factory Use)
Detector Terminal Strip
(Comb/CO2 Version Shown)
Power/Signal
Terminal Strip
3/4" NPT Conduit Opening
for Wire Entry
Relay
Terminal
Strips