RKI Instruments 65-2646XLS-SW User manual

RKI Instruments, Inc.
www.rkiinstruments.com
65-2646XLS-SW
M2A-XL Transmitter
Operator’s Manual
Part Number: 71-0652
Revision: P1
Released: 1/24/24

2• 65-2646XLS-SW M2A-XL Transmitter Operator’s Manual
WARNING
Read and understand this instruction manual before operating
instrument. Improper use of the gas monitor could result in bodily
harm or death.
Periodic calibration and maintenance of the gas monitor is essential
for proper operation and correct readings. Please calibrate and
maintain this instrument regularly! Frequency of calibration depends
upon the type of use you have and the sensor types. For most
applications, typical calibration frequencies are between 3 and 6
months but can be more often or less often based on your usage.

65-2646XLS-SW M2A-XL Transmitter Operator’s Manual • 3
Product Warranty
RKI Instruments, Inc. warrants gas alarm equipment sold by us to be free from defects in
materials, workmanship, and performance for a period of one year from the date of shipment from
RKI Instruments, Inc. Any parts found defective within that period will be repaired or replaced, at
our option, free of charge. Parts must be returned to RKI Instruments, Inc. for repair or
replacement. This warranty does not apply to those items which by their nature are subject to
deterioration or consumption in normal service, and which must be cleaned, repaired or replaced
on a routine basis. Examples of such items are:
• Absorbent cartridges
•Fuses
• Pump diaphragms and valves
•Batteries
• Filter elements
Warranty is voided by abuse including mechanical damage, alteration, rough handling, or repair
procedures not in accordance with instruction manual. This warranty indicates the full extend of
our liability, and we are not responsible for removal or replacement costs, local repair costs,
transportation costs, or contingent expenses incurred without our prior approval.
THIS WARRANTY IS EXPRESSLY IN LIEU OF ANY AND ALL OTHER WARRANTIES AND
REPRESENTATIONS, EXPRESSED OR IMPLIED, AND ALL OTHER OBLIGATIONS OR
LIABILITIES ON THE PART OF RKI INSTRUMENTS, INC. INCLUDING BUT NOT LIMITED TO,
THE WARRANTY OF MERCHANTABILITY OR FITNESS FOR APARTICULAR PURPOSE. INNO
EVENT SHALL RKI INSTRUMENTS, INC. BE LIABLE FOR INDIRECT, INCIDENTAL, OR
CONSEQUENTIAL LOSS OR DAMAGE OF ANY KIND CONNECTED WITH THE USE OF ITS
PRODUCTS OR FAILURE OF ITS PRODUCTS TO FUNCTION OR OPERATE PROPERLY.
This warranty covers instruments and parts sold to users only by authorized distributors, dealers
and representatives as appointed by RKI Instruments, Inc.
We do not assume indemnification for any accident or damage caused by the operation of this gas
monitor and our warranty is limited to the replacement of parts or our complete goods. Warranty
covers parts and labor performed at RKI Instruments, Inc. only, and does not cover field labor or
shipment of parts back to RKI.

4• 65-2646XLS-SW M2A-XL Transmitter Operator’s Manual
Table of Contents
Chapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
About the M2A Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
About this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Chapter 2: Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
External Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Internal Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Chapter 3: Installation & Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Mounting the M2A Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Wiring the M2A Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Start Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Chapter 4: Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Normal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Information Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4 - 20 mA Signal Output Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Alarm Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Chapter 5: Configuration Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Viewing & Changing M2A Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Chapter 6: Gas Type Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Selecting the Gas Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

65-2646XLS-SW M2A-XL Transmitter Operator’s Manual • 5
Chapter 7: Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Calibration Frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Replacing Components of the CO Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Chapter 8: RS-485 Modbus Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Wiring the M2A in a Modbus System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Using the M2A in a 4-wire Modbus System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Modbus Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Supported Modbus Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Chapter 9: Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Appendix A: Control Button Quick Reference Guide . . . . . . . . . . . . . . . . . . . .56
Appendix B: PLC and DCS Device Wiring. . . . . . . . . . . . . . . . . . . . . . . . . . . . .57
Appendix C: Function Code 16 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58

6• Chapter 1: Introduction 65-2646XLS-SW M2A-XL Transmitter
Chapter 1: Introduction
Overview
This chapter briefly describes the 65-2646XLS-SW M2A-XL Transmitter. This chapter also
describes the 65-2646XLS-SW M2A-XL Transmitter Operator’s Manual (this document). Table 1
at the end of this chapter lists the specifications for the M2A.
About the M2A Transmitter
The M2A transmitter is a fixed mount, continuous-monitoring detector head. All user adjustable
parameters may be accessed using push button switches. In addition, calibration may be
performed non-intrusively by use of a magnetic wand accessory which activates magnetic
switches through a window at the front face of the detector head.
The M2A displays the current gas reading on an OLED display which is visible through the
window in the cover (front face) and provides a 4 - 20 mA signal which indicates the target gas
reading for use by a gas monitoring controller, recording device, or programmable controller. The
M2A also provides an RS-485 Modbus output. Three sets of relay contacts, two controlled by the
gas alarms and one by the fail alarm, rated at 115 VAC 5 amps are available for controlling
devices such as lights or horns or for controlling higher rated relays.
Four operating modes allow you to display and change setup and calibration settings and change
the gas type. They are Calibration Mode, Configuration Mode, Gas Type Mode, and Modbus
Mode.
About this Manual
The M2A Transmitter Operator’s Manual uses the following conventions for notes, cautions, and
warnings.
NOTE: Describes additional or critical information.
CAUTION: Describes potential damage to equipment.
WARNING: Describes potential danger that can result in injury or death.

65-2646XLS-SW M2A-XL Transmitter Chapter 1: Introduction • 7
Specifications
Table 1 lists specifications for the M2A.
WARNING: When using the M2A, you must follow the instructions and warnings in this
manual to assure proper and safe operation of the M2A and to minimize the risk
of personal injury. Be sure to maintain and periodically calibrate the M2A as
described in this manual.
Table 1: M2A Specifications
Target Gas/Detection Range Carbon monoxide: 0 - 300 ppm, 1 ppm increments
Alarm Settings (Alarm 1/Alarm 2)* 25 ppm/50 ppm
Construction (housing) Explosion-proof junction box, NEMA 4X
Area Classification Explosion-proof for Class I, Groups B, C, and D
Sampling Method Diffusion
Input Power 10 - 30 VDC
Controls • Three push button switches
• Three magnetic switches for non-intrusive calibration
Weight 5.5 lbs.
Signal Output
4 to 20 mA with impedance maximums listed below:
• -12 VDC input: 500 ohms impedance max
• -24 VDC input: 1000 ohms impedance max
RS-485 Modbus
Operating Temperature -40°C to +50°C
Accuracy ± 5% of reading or ± 5 ppm CO (whichever is greater)
* These are the RKI factory settings. You can change the alarm settings in Configuration Mode. See
“Viewing & Changing M2A Parameters” on page 27.

8• Chapter 2: Description 65-2646XLS-SW M2A-XL Transmitter
Chapter 2: Description
Overview
This chapter describes the components of the M2A transmitter. The transmitter is a 4 - 20 mA
type detector head. It consists of the CO detector, terminal PCB, and the junction box.
External Description
This section describes the junction box and all external components of the M2A transmitter.
Figure 1: M2A External Components
Junction Box
The M2A’s cast aluminum junction box is dust and weather resistant. The junction box also
protects the M2A and all connections made to it. Use the three 3/4 NPT conduit hubs to mount the
detector to the junction box (factory installed in the bottom port) and connect wiring from an
external device, typically an RKI controller. The top hub is shipped with a factory installed and
sealed conduit plug to avoid leaks into the junction box. If necessary, the conduit plug can be
removed and the top hub can be used for wiring.
WARNING: If the top conduit hub is used for wiring, be sure to seal the threads to ensure
water does not enter the junction box. See “Wiring the M2A Transmitter” on
page 17 for complete wiring instructions.
3/
4NP
T
Conduit Port
,
P
lugged
1
1
/
2-20 Fo
r
C
alibration
C
u
p
3/
4NP
T
C
onduit Port
W
indo
w
M
ounting Holes
(
x2
)
CO
Detector
M
agneti
c
Wa
n
d

65-2646XLS-SW M2A-XL Transmitter Chapter 2: Description • 9
Use the junction box’s two mounting holes to mount the M2A to a vertical surface at the
monitoring site. The window in the cover on the front of the junction box allows you to view the
OLED display and use the magnetic wand to actuate the magnetic control switches so you can
perform non-intrusive calibration. Removing the cover allows you to access the interior of the
junction box.
CO Detector
The CO detector consists of the detector housing body, detector housing cap, cap gasket, charcoal
filter with rubber boot, and the plug-in sensor.
Figure 2: CO Detector Component Location
Detector Housing Body
The detector housing body protects the electronic components within the housing. Use the
mounting threads at the top of the housing to screw the CO detector into the 3/4 NPT hub on the
bottom of the detector junction box. Two wires extend from the top of the detector housing body.
Use these wires to connect the CO detector to the terminal strip. One of the wires is red and one of
the wires is black.
The housing includes a four-socket pattern. This socket pattern accepts the sensor’s four pins to
secure the sensor within the detector housing. A pre-amplifier, located between the sockets and
two interconnect wires, conditions the sensor’s signal before the signal reaches the controller.
Plug-In CO Sensor
Rubber Boot With
Charcoal Filter
Detector Housing Cap
Detector Housing Body
Cap Gasket
Flame Arrestor
Guard

10 • Chapter 2: Description 65-2646XLS-SW M2A-XL Transmitter
Housing Cap & Cap Gasket
The housing cap screws onto the detector housing. It retains the plug-in sensor and protects it
from damage. The housing cap also includes a flame arrestor which contains any sparks that may
occur within the detector and a flame arrestor guard which protects the flame arrestor from
damage. Unscrew the detector cap to access the plug-in sensor for maintenance or replacement. A
cap gasket seals the interface between the housing and cap. A flame arrestor guard is permanently
bonded to the cap.
Charcoal Filter and Rubber Boot
The disc-shaped charcoal filter is secured to the face of the CO sensor with a rubber boot. The
charcoal filter prevents interference gases (hydrogen sulfide [H2S] and certain hydrocarbons)
from producing false CO readings.
Plug-In CO Sensor
The sensor is secured within the detector assembly by the housing cap. Through a series of
chemical and electrical reactions, the sensor produces an electrical output that corresponds to the
detection range of the transmitter.
Magnetic Wand
The magnetic wand is a short plastic rod with a magnet in one end. It is used to actuate the
magnetic control switches on the control PCB while the junction box cover is still installed so that
non-intrusive calibration can be performed.

65-2646XLS-SW M2A-XL Transmitter Chapter 2: Description • 11
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 3: 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.
NO
M2A-XL TRANSMITTER
RKI INSTRUMENTS
3/4 NPT Conduit Opening
3/4 NPT Conduit
Opening for Wire Entry
Junction Box
Terminal PCB
Control PCB

12 • Chapter 2: Description 65-2646XLS-SW M2A-XL Transmitter
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 to program the M2A.
Figure 4: Terminal PCB Component Location
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 24 VDC power to the M2A 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 M2A 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. The two terminals labeled “TOXIC” are used to connect the
detector to the M2A.
NOTE: The detector is factory-wired to the M2A. See “Wiring the M2A Transmitter” on
page 17 for all wiring procedures related to M2A.
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 M2A into a Modbus
network.
Relay
Terminal
Strips
Ribbon Cable Connector
C NC NO
ALARM 1
C NC NO
ALARM 2
C NC NO
FAIL
Programming Connector
(Factory Use)
Power/Signal Terminal Strip
Detector Terminal Strip
Termination Jumper
Modbus Terminal Strip
Ground Jumper
- S+
AB C
RS 485 PWR/SIG
TOXIC OXY
+
+

65-2646XLS-SW M2A-XL Transmitter Chapter 2: Description • 13
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.
Leave this jumper installed unless directed to remove it for a Modbus installation. See “Chapter 8:
RS-485 Modbus Output” on page 42 for a description of using the M2A in a Modbus system.
Ground Jumper
A two pin header with a jumper installed is located along the left side of the terminal PCB. Leave
this jumper installed unless directed to remove it for a Modbus installation. See “Chapter 8: RS-
485 Modbus Output” on page 42 for a description of using the M2A in a Modbus system.
Control PCB
The OLED display and control switches are located on the control PCB. It is installed on top of
the terminal PCB by lining up its three spacing standoffs with the banana jacks in the terminal
PCB mounting standoffs and pushing it onto the banana jacks. The jacks retain the control PCB.
Figure 5: Control PCB Component Location
DOWN/NO
UP/YES
ENTER
Alarm 2 LED
TXLED
RX LED
OLED Display
Alarm 1 LED
Magnetic Switches
Fail LED
Push Button
Control Switches
UP/YES
DOWN/NO
ENTER
M2A-XL TRANSMITTER
RKI INSTRUMENTS

14 • Chapter 2: Description 65-2646XLS-SW M2A-XL Transmitter
OLED Display
The OLED display is located at the top of the control PCB. It indicates the current gas reading and
displays messages and parameters in the M2A’s programs.
Control Buttons
The M2A includes three push button switches that allow you to enter the M2A’s operating modes,
navigate through the modes, update settings, and save changes to the settings. The push button
switches are located along the bottom edge of the control PCB (see Figure 5). The UP/YES button
is on the left, the DOWN/NO button is in the middle, and the ENTER button is on the right.
Just above each push button switch is a magnetic switch with the same function as the push button
switch below it. The magnetic switches are for use in non-intrusive calibration. They are actuated
by bringing the magnetic wand close enough to them to actuate them. Although the magnetic
switches have the same functions as the push button switches, it is not practical to use them for
operations other than calibration because it is not possible to actuate two magnetic switches at
once with only one magnetic wand. Since displaying the Information Screen only requires the use
of one switch, the wand may be used to show the Information Screen (see “Information Screen”
on page 22).
Table 2: M2A Control Button Functions
Switch Function
UP (YES) • Saves settings
• Changes the displayed setting
• Enters the Calibration Program
• Enters Gas Type Mode (press with DOWN/NO
button)
• Enters Configuration Mode (press with ENTER
button)
DOWN
(NO)
• Cancels setting changes
• Changes the displayed setting
• Enters Gas Type Mode (press with UP/YES button)
• Enters Modbus Mode (press with ENTER button)
• Displays the Information Screen
ENTER • Initiates operations
• Enters Configuration Mode (press with UP/YES
button)
• Enters Modbus Mode (press with DOWN/NO button)
• Functions as an alarm reset switch

65-2646XLS-SW M2A-XL Transmitter Chapter 2: Description • 15
Status LEDs
The M2A includes five status LEDs that are located above the display (see Figure 5).
• Fail LED
The fail LED turns on when the M2A is experiencing a fail condition. A fail condition can
be caused by a detector failure or low detector signal.
• Alarm 1 LED
The alarm 1 LED is on when the M2A is experiencing an alarm 1 condition.
• Alarm 2 LED
The alarm 2 LED is on when the M2A is experiencing an alarm 2 condition.
• RX & TX LED’s
These LED’s indicate data being received (RX) and transmitted (TX) when the M2A’s
Modbus output is operating.

16 • Chapter 3: Installation & Startup 65-2646XLS-SW M2A-XL Transmitter
Chapter 3: Installation & Startup
Overview
This chapter describes procedures to mount the M2A Transmitter in the monitoring environment
and wire it to input power and devices.
Mounting the M2A Transmitter
1. Select a mounting site that is representative of the monitoring environment. Consider the
following when you select the mounting site.
• Select a site where the junction box is not likely to be bumped or disturbed. Make sure
there is sufficient room to perform start-up, maintenance, and calibration procedures. The
site should be easily accessible.
• Select a site where the target gas is likely to be found first. For lighter gases, mount the
detector near the ceiling; for heavier gases, mount the detector near the floor.
2. Use #10 screws through the M2A junction box’s two mounting holes to secure the junction
box to a vertical surface. Figure 6 shows the outline and mounting dimensions. Mount the
M2A with the detector facing down as shown in Figure 6.
Figure 6: Outline & Mounting Dimensions
1 1/2-20 Fo
r
C
alibration Cup
3/
4NPT
C
onduit Port,
Plu
gg
ed
3.4 ma
x
6
.
2
1.
93
3/4 NPT
C
onduit Port
8.6 ma
x
1.0
2
Ø
0.25, 2X
5.5
2
.
25
1.1
2

65-2646XLS-SW M2A-XL Transmitter Chapter 3: Installation & Startup • 17
Wiring the M2A Transmitter
WARNING: Always verify that the power to the M2A is off before you make wiring
connections.
1. Confirm that no power is being applied to the M2A.
2. Remove the junction box cover.
3. Grasp the control PCB by its edges.
4. Gently pull until the control PCB is pulled away from the banana jacks. Take care not to pull
too hard and damage the cable which connects the control and terminal PCBs.
5. Let the control PCB hang by the cable. The terminal strips are now visible on the terminal
PCB. The control PCB may be left hanging while wiring is done. If desired, the control PCB
may be disconnected from the cable and set aside while wiring.
6. The detector leads are factory wired. Verify that the detector leads are wired to the detector
terminal strip as shown in the figure below.
Figure 7: Wiring the Detector to the M2A
7. To gain access to a plug-in terminal strip for wiring, pull it out of its socket by grasping the
wall between two terminal positions with needle nose pliers and pulling. Be careful not to
exert too much force on the wall to avoid damage to the terminal strip. The detector terminal
strip and the alarm 1 relay terminal strip may be removed by grasping them with your fingers
if the adjacent terminal strips have been removed.
Black
Red
C NC NO
ALARM 1 C NC NO
ALARM 2
C NC NO FAIL
- S +
PWR/SIG
TOXIC OXY
+ - + -
RS 485
A B C

18 • Chapter 3: Installation & Startup 65-2646XLS-SW M2A-XL Transmitter
WARNING: If the controller’s construction is not explosion-proof, the controller must be
installed in an ordinary location. Do not install a non-explosion-proof
controller in a classified location.
If the controller’s construction is explosion-proof and the controller is
installed in a classified location, install a conduit seal at the controller’s wire
entry location that is consistent with the controller’s explosion-proof rating.
WARNING: If the M2A is installed in a hazardous location, use appropriately rated
conduit, conduit fittings, and appropriate construction technique that
complies with the local electrical code.
In addition, use appropriately rated conduit, conduit fittings, and appropriate
construction technique to maintain the NEMA 4X environmental rating of
the junction box and avoid water entering the junction box at the conduit
ports.
8. To maintain the explosion proof classification of the M2A junction box, a conduit seal must
be installed within 2 inches (for Group B environments) or 18 inches (for Groups C and D
environments) of the M2A’s left conduit hub. Adhere to your local electrical code when
installing the conduit seal.
9. Guide multi conductor shielded cable or cables or wires in conduit through the left conduit
hub of the M2A junction box. The number of cables or wires needed will depend on whether
the M2A is wired to a gas monitoring controller or just to power, whether any relays are used,
and whether the Modbus output is used.
WARNING: If the top conduit hub is used for wiring, be sure to seal the threads to ensure
water does not enter the junction box. A conduit seal, which is normally
required to maintain the junction box’s hazardous location rating, will also
help to prevent water from entering through the top port.
NOTE: If the M2A is being wired to a PLC or DCS device, see “Appendix B: PLC
and DCS Device Wiring” on page 57, then continue with step 8.

65-2646XLS-SW M2A-XL Transmitter Chapter 3: Installation & Startup • 19
Use the following recommendations to determine how to wire the M2A:
• If Modbus connections will not be used and only the PWR/SIG connections will be used,
use a two or three conductor shielded cable or two or three wires in conduit for
connections to the power/signal terminal strip depending on whether or not the signal (S)
terminal is used. The S terminal has a 4 - 20 mA output, but if you do not need to monitor
this signal and do not connect to the S terminal to access this signal, the M2A will still
function completely.
• If the PWR/SIG connections and one or more relays are used, route the connections to the
M2A in conduit. Use shielded cable in the conduit for the PWR/SIG connections and
unshielded cable or individual wires for the relay connections. Make sure any wire or
cable used for relay wiring is appropriately rated for the power that it will carry.
CAUTION: If shielded cable is used for the PWR/SIG connections, leave the cable
shield’s drain wire insulated and disconnected at the M2A junction box.
You will connect the opposite end of the cable’s drain wire at the
controller or device.
• If the M2A will be wired into a Modbus network, see “Chapter 8: RS-485 Modbus
Output” on page 42.
See Figure 8 below for field wiring connections to the M2A.
Figure 8: Wiring the M2A Junction Box to a Controller and Alarm Devices
Table 3: Wire Size for PWR/SIG Connections
Max Distance to
Controller
w/18 Gauge Wire
Max Distance to
Controller w/16 Gauge
Wire
Max Distance to
Controller w/14 Gauge
Wire
2,500 ft. 5,000 ft. 8,000 ft.
Fail Alarm
Device
Alarm 1
Alarm Device
Alarm Device
Power
Typical Alarm
Wiring Shown
See
Detector
Wiring
Alarm 2
Alarm Device
RKI Controller
Terminals
(24 VDC) +
4-20mAIn (S)
(24 VDC) -
See
Modbus
Wiring
C NC NO
C NC NO
ALARM 2
C NC NO
FAILALARM 1
AB C
RS 485
- S+
PWR/SIG
TOXIC OXY
+ +

20 • Chapter 3: Installation & Startup 65-2646XLS-SW M2A-XL Transmitter
10. Re-install the control PCB (and ribbon cable if necessary). Be sure the ribbon cable is routed
down below the control PCB so it will not be damaged by the cover when it is screwed back
on.
11. Secure the junction box cover to the junction box.
12. Make controller, device, and relay connections as appropriate. If shielded cable is used for the
PWR/SIG connections, connect the cable shield’s drain wire to an available chassis ground at
the gas monitoring controller, recording device, or programmable controller.
Start Up
Introducing Incoming Power
1. Complete the installation procedures described earlier in this manual.
2. Verify that all wiring connections are correct and secure.
3. Turn on the incoming power.
4. If necessary, turn on the controller or other monitoring device that is connected to the M2A.
5. The OLED display will indicate the firmware version when the M2A is first powered up and
will then count down a one minute warm-up period before normal operation begins. During
normal operation, the display will indicate the target gas and current gas reading. Verify that
the display is indicating the target gas and current gas reading after the warm-up period is
complete and normal operation begins.
NOTE: Allow the M2A’s detector to warm up for 15 minutes before you continue
with the next section, “Adjusting the Fresh Air Reading.”
Adjusting the Fresh Air Reading
When the M2A is shipped from RKI Instruments, Inc., it is factory calibrated. If a full calibration
is desired at startup, see “Calibration” on page 36.
Verify that the M2A is in a fresh air environment (environment known to be free of combustible
or toxic gas vapors and of normal oxygen content, 20.9%).
CAUTION: If you suspect the presence of carbon monoxide in the monitoring environment, use
the calibration kit and the zero air calibration cylinder to introduce “fresh air” to
the detector and verify an accurate fresh air setting. See the “Calibration” on
page 36 for instructions on how to use a zero air cylinder when performing a fresh
air adjustment.
CO
0 ppm