RKI Instruments M2A - Manual (Page 15)

M2A Transmitter Operator’s Manual 10
Internal Description
This section describes the internal components of the M2A. The internal components of the M2A
include the terminal PCB which provides for all the wiring connections to the M2A and the control
PCB which displays the gas reading and has the control buttons.
Figure 9: M2A 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 OLED 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 M2A 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 M2A.
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
TX LED
RX LED
Alarm 2 LED
N
O
ENTER
DOW N/NO
-
S
+
A
B
C
RS
4
8 5
PW
R /S
IG
R
W
G
B
LE
L
Fail LED
Alarm 1 LED
Termination Jumper
Modbus Terminal Strip
Programming
Connector
(Factory Use)
Ground Jumper
Detector Terminal Strip
(Comb/CO2 Version Shown)
C
NC
NO
AL
AR
M
1
C
NC
NO
AL
A
R M
2
C
NC
NO
FA
IL
UP/YES
DOW N/NO
Push Button
Control Switches
Control PCB
Magnetic
Switches
Junction Box
Terminal PCB
Detector Current
Adjust Pot
(Comb/CO2 Type Only,
Factory Adjust)
ENTER
UP/YES
M 2A T R AN SM IT TE R
R K I IN ST RU M EN TS
OLED Display
View With Cover Removed
View With Cover and
Control PCB Removed
Ribbon Cable Connector
3/4" NPT Conduit Opening, Plugged
Power/Signal
Terminal Strip
3/4" NPT
Conduit
Opening
for Wire
Entry
Relay
Terminal
Strips