RKI Instruments 65-2646XL-05-04 User manual

RKI Instruments, Inc.
www.rkiinstruments.com
65-2646XL-05-04
M2A Transmitter
Operator’s Manual
Part Number: 71-0612
Revision: P1
Released: 10/20/22

2• 65-2646XL-05-04 M2A 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. Typical
calibration frequencies for most applications are between 3 and 6
months, but can be required more often or less often based on your
usage.

65-2646XL-05-04 M2A 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 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. 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 the operator’s manual. This warranty indicates the full extent
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 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.

4• 65-2646XL-05-04 M2A 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Start Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Chapter 4: Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Normal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Information Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4 - 20 mA Signal Output Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Alarm Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Chapter 5: Configuration Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Viewing & Changing M2A Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Chapter 6: Gas Type Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Selecting the Gas Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

65-2646XL-05-04 M2A Transmitter Operator’s Manual • 5
Chapter 7: Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Calibration Frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Replacing Components of the CO Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Chapter 8: RS-485 Modbus Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Wiring the M2A in a Modbus System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Using the M2A in a 4-wire Modbus System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Modbus Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Supported Modbus Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Chapter 9: Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Appendix A: Control Button Quick Reference Guide . . . . . . . . . . . . . . . . . . . . 61
Appendix B: PLC and DCS Device Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Appendix C: Function Code 16 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

65-2646XL-05-04 M2A Transmitter Operator’s Manual Chapter 1: Introduction • 6
Chapter 1: Introduction
Overview
This chapter briefly describes the 65-2646XL-05-04 M2A Transmitter. This chapter also
describes the 65-2646XL-05-04 M2A 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.

7• Chapter 1: Introduction 65-2646XL-05-04 M2A Transmitter Operator’s Manual
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: 500 ohms impedance max
-24 VDC: 1000 ohms impedance max
• RS-485 Modbus
Operating Temperature -5°C to 40°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 30.

65-2646XL-05-04 M2A Transmitter Operator’s Manual Chapter 2: Description • 8
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, calibration adapter/splash guard, terminal PCB,
the M2A junction box, and the detector junction box. The two junction box configuration is
intended for situations where the detector needs to be installed at an inaccessible location. The
detector junction box can be installed at the inaccessible location and the M2A junction box can
be installed in a more readily accessible area.
External Description
This section describes the junction boxes and all external components of the M2A transmitter.
Figure 1: M2A External Components
Carbon Monoxide
Detector
Detector
Junction Box
Calibration Adapter/
Splash Guard
Terminal
Strip
Window
3/4 NPT
Conduit Hub
M2A-XL
Junction
Box
3/4 NPT
Conduit Hub
Magnetic
Wand
3/4 NPT Conduit Port
Mounting Hole (2x)

9• Chapter 2: Description 65-2646XL-05-04 M2A Transmitter Operator’s Manual
M2A 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 wire the
remotely installed combustible gas detector 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 18 for complete wiring instructions.
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.
Detector Junction Box
The detector junction box is intended to be installed remotely from the M2A junction box. The
CO detector is factory installed in the bottom 3/4 NPT conduit hub. A terminal strip is provided
for wiring connections and the detector is factory wired to one side of this terminal strip. The
other side of the terminal strip is for user-supplied wiring to the detector terminal strip located in
the M2A junction box. This wiring should go through the top 3/4 NPT conduit hub. Three spacers
installed on the back of the junction box controls the distance of the junction box from a mounting
surface. A ground boss near the top conduit hub provides an external earth ground connection.

65-2646XL-05-04 M2A Transmitter Operator’s Manual Chapter 2: Description • 10
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.
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
Rubber Boot With
Charcoal Filter
Detector Housing Cap
Detector Housing Body
Cap Gasket
Flame Arrestor
Guard

11 • Chapter 2: Description 65-2646XL-05-04 M2A Transmitter Operator’s Manual
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.
Calibration Adapter/Splash Guard
A calibration adapter/splash guard is installed on the CO detector. A fitting at the bottom of the
calibration adapter/splash guard allows a length of tubing to be connected for calibration and
routed to a more easily accessible location (near the M2A junction box is optimal for ease of
calibration). The calibration adapter/splash guard also protects the detector from splashing water
or direct water spray.
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.
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
NO
Control PCB
Terminal PCB
M2A-XL TRANSMITTER
Junction Box
3/4 NPT Conduit Opening
3/4 NPT Conduit
Opening for Wire Entry RKIINSTRUMENTS

65-2646XL-05-04 M2A Transmitter Operator’s Manual Chapter 2: Description • 12
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 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).
C NC NO
ALARM 1 C NC NO
ALARM 2
C NC NO FAIL
Modbus Terminal Strip
Ground Jumper
Programming Connector
(Factory Use)
Termination Jumper
Relay
Terminal
Strips
RS 485
A B C - S +
PWR/SIG
+
Ribbon Cable Connector
Power/Signal Terminal Strip
Detector Terminal Strip
TOXIC OXY
+

13 • Chapter 2: Description 65-2646XL-05-04 M2A Transmitter Operator’s Manual
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 18. 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
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 48 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 48 for a description of using the M2A in a Modbus system.

65-2646XL-05-04 M2A Transmitter Operator’s Manual Chapter 2: Description • 14
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
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.
ENTER
UP/YES
DOWN/NO
ENTER
DOWN/NO
UP/YES
Push Button
Control Switches
Fail LED
Magnetic Switches
Alarm 1 LED
OLED Display
RX LED
TX LED
Alarm 2 LED
M2A-XL TR ANSMITTER
RKI INSTRUMENTS

15 • Chapter 2: Description 65-2646XL-05-04 M2A Transmitter Operator’s Manual
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 25).
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.
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

65-2646XL-05-04 M2A Transmitter Operator’s Manual Chapter 3: Installation & Startup • 16
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.
• For the M2A junction box, 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.
• For the detector junction box, 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.
• The junction boxes should be mounted no further than 200 feet from each other.
2. Use #10 screws through the M2A junction box’s two mounting slots to secure the junction
box to a vertical surface. Figure 6 shows the outline and mounting dimensions the M2A
junction box. Figure 7 shows the outline and mounting dimensions for the detector junction
box. Mount the detector junction box with the detector facing down as shown in Figure 7.
Figure 6: Outline & Mounting Dimensions, M2A Junction Box
3/4 NPT
Conduit Port
1.00
4.86
3/4 NPT
Conduit Port
Ø0.25,2X
5.5
5.66
2.82
6.2

17 • Chapter 3: Installation & Startup 65-2646XL-05-04 M2A Transmitter Operator’s Manual
Figure 7: Outline & Mounting Dimensions, Detector Junction Box
3. Install 3/16 inch I.D. flexible polyurethane tubing to the fitting at the bottom of the calibration
adapter/splash guard and route it to an accessible area that is close to the M2A junction box.
See the “Chapter 9: Parts List” on page 60 for available tubing.
.382.70
CO
Detector
Calibration
Adapter/
Splash
Guard
3/4 Conduit Hub Ø3.65
11.60 Max
5.25
Rubber
Spacer,
3X
1.13

65-2646XL-05-04 M2A Transmitter Operator’s Manual Chapter 3: Installation & Startup • 18
Wiring the M2A Transmitter
Wiring the Detector to the M2A
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 detector junction box’s cover from the junction box.
3. Remove the M2A junction box’s cover from the junction box.
4. Grasp the control PCB by its edges.
5. 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.
6. 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.
7. To maintain the explosion proof classification of the junction boxes, conduit seals must be
installed as shown in Figure 8. Adhere to your local electrical code when installing the conduit
seal.
8. To maintain the M2A junction box’s NEMA 4X environmental rating and prevent water from
entering the junction box through the conduit hubs, use appropriate construction technique.
9. Guide a two-conductor, shielded cable or two wires in conduit through the top conduit hub of
the detector junction box. To make wiring more convenient, use wire colors that correspond to
the detector wire colors: red and black.
10. Connect the wires to the terminal block in the detector junction box.
11. Secure the detector junction box’s cover to the junction box.
12. Guide the other end of the two-conductor, shielded cable or two wires in conduit through the
bottom conduit hub of the M2A junction box.
Max Distance to
M2A w/18 Gauge
Wire
Max Distance to
M2A w/16 Gauge
Wire
Max Distance to
M2A w/14 Gauge
Wire
500 ft. 1,000 ft. 2,000 ft.

19 • Chapter 3: Installation & Startup 65-2646XL-05-04 M2A Transmitter Operator’s Manual
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.
13. 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.

65-2646XL-05-04 M2A Transmitter Operator’s Manual Chapter 3: Installation & Startup • 20
14. Pull out the detector terminal strip and connect the two wires to the terminal strip as follows
(see Figure 8).
• Connect the wire corresponding to the detector’s red wire to the TOXIC “+” terminal.
• Connect the wire corresponding to the detector’s black wire to the TOXIC “-” terminal.
CAUTION: If shielded cable is used, leave the cable shield’s drain wire disconnected and
insulated at the detector junction box. You will connect the opposite end of the
cable’s drain wire to the M2A junction box’s chassis (earth) ground.
Figure 8: Wiring the Detector to the M2A
15. Reinstall the detector terminal strip into its socket.
16. If shielded cable is used between the detector junction box and the M2A junction box, connect
the cable’s drain wire to an available chassis (earth) ground at the M2A junction box. Do not
connect the shield drain wire at the detector junction box.
Black
Red
Red
Black
Cable
Shield
C NC NO
ALARM1 C NC NO
ALARM 2
C NC NO FAIL
TOXIC OXY
A B C
RS 485 +
+
PWR/SIG
- S +
Install conduit seal within
2 inches (for Group B
environments) or 18
inches (for Groups C and
D environments)
Calibration Adapter/Splash Guard
Detector J-Box
CO Detector
Install conduit seal
within 2 inches
M2A-XL
J-Box
3/4 NPT Conduit Opening
Detector
Terminal
Strip