RKI Instruments 65-2640RK-03 User manual

RKI Instruments, Inc.
www.rkiinstruments.com
65-2640RK-03
M2A Transmitter
Operator’s Manual
Part Number: 71-0332
Revision: F
Released: 8/28/20

2 65-2640RK-03 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-03 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:
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

4 65-2640RK-03 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Selecting the Gas Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

65-2640RK-03 M2A Transmitter Operator’s Manual 5
Chapter 7: Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Calibration Frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Replacing the Combustible Gas Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Chapter 8: RS-485 Modbus Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Wiring the M2A in a Modbus System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Using the M2A in a 4-wire Modbus System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Modbus Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Supported Modbus Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Chapter 9: Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Appendix A: Control Button Quick Reference Guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Appendix B: PLC and DCS Device Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Appendix C: Function Code 16 Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

6 65-2640RK-03 M2A Transmitter Operator’s Manual
Chapter 1: Introduction
Overview
This chapter briefly describes the 65-2640RK-03 M2A Transmitter. This chapter also describes the 65-2640RK-
03 M2ATransmitter 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-03 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 27.

8 65-2640RK-03 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, 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 Hub
Magnetic
Wand
Terminal
Strip
3/4 NPT Conduit
Hub, Plugged
M2A
Junction
Box
Combustible Gas
Detector
Detector
Junction Box
3/4 NPT
Conduit Hub
Calibration Adapter
3/4 NPT
Conduit Hub
Mounting Slot (2x)
Window

65-2640RK-03 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 M2ATransmitter” 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.
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 also contains any 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. 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
A calibration adapter is installed on the combustible gas detector. A fitting at the bottom of the calibration
adapter 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).
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-03 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
Junction Box
Terminal PCB
3/4 NPT Conduit
Opening forWireEntry
M2A TRANSMITTER
RKI INSTRUMENTS
3/4 NPT Conduit Opening, Plugged

65-2640RK-03 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-03 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 40 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 40 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
M2A TRANSMITTER
RKI INSTRUMENTS
OLED Display

65-2640RK-03 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 22).
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-03 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-03 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 and
route it to an accessible area that is close to the M2A junction box. See the “Chapter 9: Parts List” on
page 50 for available tubing.
Ø3.65
3/4 Conduit Hub .382.70
Combustible
Gas
Detector
Calibration
Adapter
1.13
9.25 Max
5.25
Rubber
Spacer,
3X

16 65-2640RK-03 M2A Transmitter Operator’s Manual
Wiring the M2A Transmitter
Wiring the Detector to the M2A
WARNING: Always verify that the power to the M2Ais 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 7. Adhere to your local electrical code when installing the conduit seal.
8. Guide multi conductor shielded cable or cables or 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, white, green, and black.
9. Connect the wires to the terminal block in the detector junction box.
10. Secure the detector junction box’s cover to the junction box.
11. Guide the other end of the four-conductor, shielded cable or four wires in conduit through the M2A junction
box’s bottom conduit hub.
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.
12. 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.
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.

65-2640RK-03 M2A Transmitter Operator’s Manual 17
13. 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.
Figure 7: Wiring the Detector to the M2A
14. Reinstall the detector terminal strip into its socket.
15. 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.
Red
White
Green
Black
Cable
Shield
Detector
Terminal
Strip
C NC NO
ALARM 1 C NC NO
ALARM2
C NC NO FAIL
Green
White
Install conduit seal
within 18 inches
Detector J-Box
Red
Black
M2A
J-Box
Calibration Adapter
Combustible Gas
Detector
Install conduit seal within
2 inches (for Group B
environments) or 18
inches(for Groups C and
D environments)
- S +
A B C
RS 485 PWR/SIG
R W G B
LEL

18 65-2640RK-03 M2A Transmitter Operator’s Manual
Wiring the M2A to a Controller and Alarm Devices
WARNING: If the controller’s construction is not explosion-proof, the controller must be installed in an
ordinary location. Do non install a non-explosion-proof controller in a classified location.
1. 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, in addition to the conduit seals shown in Figure 7. Adhere to your local electrical code
when installing the conduit seal.
2. 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 52, 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 ter-
minal 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 con-
duit. 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 40.
See Figure 8 below for field wiring connections to the M2A.
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 DistancetoController w/14 Gauge Wire
2,500 ft. 5,000 ft. 8,000 ft.

65-2640RK-03 M2A Transmitter Operator’s Manual 19
Figure 8: Wiring the M2A Junction Box to a Controller and Alarm Devices
3. 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.
4. Secure the M2A junction box cover to the junction box.
5. 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

20 65-2640RK-03 M2A Transmitter Operator’s Manual
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 combustible gas 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.
Non-Intrusive Fresh Air Signal Adjustment
If the M2A is installed in a classified area and non-intrusive zero adjustment is required, follow the instructions
below, but do not remove the junction box cover. Use the magnetic wand accessory to actuate the magnetic
switches instead of pushing the control switch buttons. To actuate a magnetic switch and perform the same
operation as pressing a control switch button, touch the magnet in the end of the magnetic wand to the M2A’s
glass cover directly over the magnetic switch you wish to actuate. Touching the glass and removing the wand is
the same as pressing and releasing a button. Touching the glass and keeping the wand in place is the same as
pressing and holding a button.
WARNING: The M2Ais not an active gas monitoring device during the fresh air adjustment procedure.
The 4-20 mA output signal will “freeze” at 3.5 mA and all relays will remain in their non-
alarm state while the M2Ais in Calibration Mode. The output signal will not indicate current
readings and the relays will not resume operating normally until the M2A is in normal
operation again.
METHANE
0 %LEL