RKI Instruments 65-2640RK-05-04 User manual

RKI Instruments, Inc.
www.rkiinstruments.com
65-2640RK-05-04
M2A Transmitter
Operator’s Manual
Part Number: 71-0406
Revision: A
Released: 9/20/18

65-2640RK-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.

65-2640RK-05-04 M2A Transmitter Operator’s Manual
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:
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 A
PARTICULAR PURPOSE. IN NO 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.
a) Absorbent cartridges d) Batteries
b) Pump diaphragms and valves e) Filter elements
c) Fuses

65-2640RK-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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Chapter 3: Installation & Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Mounting the M2A Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Wiring the M2A Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Start Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Chapter 4: Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Normal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Information Screen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4 - 20 mA Signal Output Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Alarm Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Chapter 5: Configuration Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Viewing & Changing M2A Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Chapter 6: Gas Type Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Selecting the Gas Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

65-2640RK-05-04 M2A Transmitter Operator’s Manual
Chapter 7: Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Calibration Frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Replacing the Combustible Gas Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Chapter 8: RS-485 Modbus Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Wiring the M2A in a Modbus System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Using the M2A in a 4-wire Modbus System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Modbus Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Supported Modbus Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Appendix A: Control Button Quick Reference Guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Appendix B: PLC and DCS Device Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Appendix C: Function Code 16 Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
(Appendix C available from RKI Instruments, Inc. Not included in manual as normally
provided with M2A detector head.)

6 65-2640RK-05-04 M2A Transmitter Operator’s Manual
Chapter 1: Introduction
Overview
This chapter briefly describes the 65-2640RK-05-04 M2A Transmitter. This chapter also
describes the 65-2640RK-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.

65-2640RK-05-04 M2A Transmitter Operator’s Manual 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 Combustible Gas (methane calibration standard):
0 - 100% LEL, 1% LEL increments
Alarm Settings
(Alarm 1/Alarm 2) 10 %LEL/50 %LEL
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 ± 2% LEL (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 28.

8 65-2640RK-05-04 M2A Transmitter Operator’s Manual
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 combustible gas 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
3/4" NPT Conduit Hub3/4" NPT Conduit
Hub, Plugged Terminal
Strip
Magnetic
Wand
Combustible Gas
Detector
Calibration Adapter/
Splash Guard
3/4" NPT
Conduit Hub
Detector
Junction Box
Window
3/4" NPT
Conduit Hub
Mounting Slot (2x)
M2A
Junction Box

65-2640RK-05-04 M2A Transmitter Operator’s Manual 9
M2A Junction Box
The M2A’s cast aluminum junction box protects the terminal PCB and wiring connections
made to the terminal PCB. 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 16 for complete wiring instructions.
Use the junction box’s two mounting slots 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 combustible gas detector is factory installed in the bottom 3/4 NPT conduit hub using
a 3/4 x 1/2 NPT reducer. 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.
Combustible Gas Detector
The combustible gas detector is a catalytic type detector that produces an electrical output
that corresponds to the detection range. It is packaged in a 1/2 NPT nipple with a sintered
metal flame arrestor on one end allowing ambient air to diffuse into the detector. The
flame arrestor alsocontainsany sparks which may occur within the detector. The 1/2 NPT
mounting threads at the top of the detector allow you to mount it into the bottom conduit
hub of the junction box. The junction box conduit hub is 3/4 NPT, so a 3/4 x 1/2 NPT
reducer is used to install the combustible gas detector. A flame arrestor guard is located at
the bottom of the detector and is permanently bonded to the detector housing. The flame
arrestor guard protects the flame arrestor from impact damage. Four color-coded leads
extend from the top of the detector. The leads allow you to connect the detector to the
terminal strip.
Calibration Adapter/Splash Guard
A calibration adapter/splash guard is installed on the combustible gas 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.

10 65-2640RK-05-04 M2A Transmitter Operator’s Manual
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 2: 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 to program the M2A. A factory adjust pot
just above the programming connector is used to set the detector current.
NO
Control PCB
M2A TRANSMITTER
RKI INSTRUMENTS
3/4" NPT Conduit Opening, Plugged
M2A JunctionBox
3/4" NPT Conduit
Opening for Wire Entry
Terminal PCB

65-2640RK-05-04 M2A Transmitter Operator’s Manual 11
Figure 3: 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. All four terminals 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 16 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.
Relay
Terminal
Strips
Ribbon Cable Connector
Termination Jumper
Detector Terminal Strip
Power/Signal Terminal Strip
Detector Current Adjust Pot
Programming Connector
(Factory Use)
Ground Jumper
Modbus Terminal Strip
C NC NO
ALARM 1 C NC NO
ALARM 2
C NC NO FAIL
- S +
A B C
RS 485 PWR/SIG
R W G B
LEL

12 65-2640RK-05-04 M2A Transmitter Operator’s Manual
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 41 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 41 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 4: 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 4). 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
DOWN/NO
UP/YES
Push Button
Control Switches
Magnetic Switches
ENTER
UP/YES
DOWN/NO
Alarm 1 LED Alarm 2 LED
Fail LED RX LED
TX LED
M2ATRANSMITTER
RKI INSTRUMENTS
OLED Display

65-2640RK-05-04 M2A Transmitter Operator’s Manual 13
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 23).
Status LEDs
The M2A includes five status LEDs that are located above the display (see Figure 4).
• 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

14 65-2640RK-05-04 M2A Transmitter Operator’s Manual
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 5 shows the outline and mounting
dimensions the M2A junction box. Figure 6 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 6.
Figure 5: Outline & Mounting Dimensions, M2A Junction Box
.30 (2X)
3/4 NPT
Conduit Hub
5.23
.47 (2X)
2.41
5.00
1.02
5.86
4.59

65-2640RK-05-04 M2A Transmitter Operator’s Manual 15
Figure 6: 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 “Parts List” on page 51 for available tubing.
.382.70
Calibration
Adapter/
Splash
Guard
3/4 Conduit Hub Ø3.65
Combustible
Gas
Detector
5.25
9.80 Max
Rubber
Spacer,
3X
1.13

16 65-2640RK-05-04 M2A Transmitter Operator’s Manual
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 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. Guide multi conductor shielded cable or cables or wires in conduit through the
conduit hub on the left side of the junction box. To make wiring more convenient, use
wire colors that correspond to the detector wire colors: red, white, green, and black.
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: Consult RKI Instruments, Inc. for cable lengths longer than 200 feet.
8. Connect the wires to the terminal block in the detector junction box.
9. Secure the detector junction box’s cover to the junction box.
10. Guide the other end of the four-conductor, shielded cable or four wires in conduit
through the bottom conduit hub of the M2A junction box.
11. 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.
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 4
environmental rating of the junction box and avoid water entering the
junction box at the conduit hubs.

65-2640RK-05-04 M2A Transmitter Operator’s Manual 17
12. Pull out the detector terminal strip and connect the four wires to the terminal strip as
follows (see Figure 7).
• Connect the wire corresponding to the detector’s red wire to the LEL “R”
terminal.
• Connect the wire corresponding to the detector’s white wire to the LEL “W”
terminal.
• Connect the wire corresponding to the detector’s green wire to the LEL “G”
terminal.
• Connect the wire corresponding to the detector’s black wire to the LEL “B”
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.

18 65-2640RK-05-04 M2A Transmitter Operator’s Manual
Figure 7: Wiring the Detector to the M2A
13. Reinstall the detector terminal strip into its socket.
14. 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.
15. Guide multi conductor shielded cable or cables or wires in conduit through the top
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.
Detector
Terminal
Strip
C NC NO
ALARM 1 C NC NO
ALARM2
C NC NO FAIL
Cable
Shield
Black
Green
White
Red
Detector J-Box
Combustible Gas
Detector
Calibration Adapter/Splash Guard
M2A
J-Box
Black
Red
White
Green
- S +
A B C
RS 485 PWR/SIG
R W G B
LEL

65-2640RK-05-04 M2A Transmitter Operator’s Manual 19
NOTE: If the M2A is being wired to a PLC or DCS device, see “Appendix B: PLC and
DCS Device Wiring” on page 53, then continue with step 8.
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 41.
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 toController w/14 Gauge Wire
2,500 ft. 5,000 ft. 8,000 ft.

20 65-2640RK-05-04 M2A Transmitter Operator’s Manual
See Figure 8 below for field wiring connections to the M2A.
Figure 8: Wiring the M2A Junction Box to a Controller and Alarm Devices
16. 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.
17. Secure the M2A junction box cover to the junction box.
18. 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.
Alarm Device
Power
Typical Alarm
WiringShown
Fail Alarm
Device
Alarm 1
Alarm Device
RKI Controller
Terminals
(24 VDC) +
4 - 20 mA In (S)
(24 VDC) -
Alarm 2
Alarm Device
See
Modbus
Wiring
- S +
A B C
RS 485 PWR/SIG
R W G B
LEL
See
Detector
Wiring
C NC NO
ALARM 1 C NC NO
ALARM 2
C NC NO FAIL