RKI Instruments M2A-XL User manual

RKI Instruments, Inc.
www.rkiinstruments.com
M2A-XL Transmitter
Operator’s Manual
Part Number: 71-0610
Revision: P1
Released: 10/20/22

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

M2A-XL Transmitter Operator’s Manual • 3
Product Warranty
RKI Instruments, Inc. warrants gas alarm equipment sold by us to be free from defects in
materials, workmanship, and performance for a period of one year from 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
• Pump diaphragms and valves
•Fuses
•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• M2A-XL Transmitter Operator’s Manual
Table of Contents
Chapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
About the M2A-XL Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
About this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Chapter 2: Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
External Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Internal Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Chapter 3: Installation & Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Mounting the M2A-XL Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Wiring the M2A-XL Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Start Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Chapter 4: Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Normal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Information Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4 - 20 mA Signal Output Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Alarm Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Chapter 5: Configuration Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Viewing & Changing M2A-XL Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Chapter 6: Gas Type Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Selecting the Gas Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Chapter 7: Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Calibration Frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Calibration, Combustible Gas, CO2, and Toxic Versions . . . . . . . . . . . . . . . . . . . . . . . . 58

M2A-XL Transmitter Operator’s Manual • 5
Calibration, Oxygen Version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Replacing Components of the M2A-XL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Chapter 8: RS-485 Modbus Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Wiring the M2A-XL in a Modbus System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Using the M2A-XL in a 4-wire Modbus System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Modbus Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Supported Modbus Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Chapter 9: Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Appendix A: Control Button Quick Reference Guide . . . . . . . . . . . . . . . . . . . .91
Appendix B: PLC and DCS Device Wiring. . . . . . . . . . . . . . . . . . . . . . . . . . . . .92
Appendix C: Function Code 16 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

6• Chapter 1: Introduction M2A-XL Transmitter Operator’s Manual
Chapter 1: Introduction
Overview
This chapter briefly describes the M2A-XL Transmitter. This chapter also describes the M2A-XL
Transmitter Operator’s Manual (this document). Table 1 at the end of this chapter lists the
specifications for the M2A-XL.
About the M2A-XL Transmitter
The M2A-XL 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-XL 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-XL 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-XL 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.

M2A-XL Transmitter Operator’s Manual Chapter 1: Introduction • 7
Specifications
Table 1 lists specifications for the M2A-XL.
Table 1: M2A-XL Specifications
Target Ga s/
Detection Range
Combustible Gas/Carbon Dioxide (CO2)
• Catalytic LEL: 0 - 100% LEL, 1% LEL increments (CH4calibration unless
otherwise specified. H2specific detector available)
• Catalytic CH4ppm: 0 - 9000 ppm, 20 ppm increments
• IR (infrared) CH4LEL: 0 - 100% LEL, 1% LEL increments
• IR HC LEL: 0 - 100% LEL, 1% LEL increments (propane calibration)
• IR CH4Volume: 0 - 5.00% volume, 0.01% increments
• IR CH4Volume: 0 - 100% volume, 1% increments
• IR CO2ppm: 0 - 5,000 ppm, 20 ppm increments
• IR CO2ppm: 0 - 10,000 ppm, 20 ppm increments
• IR CO2Volume: 0 - 5.00% volume, 0.01% increments
• IR CO2Volume: 0 - 50.0% volume, 0.1% increments
• IR CO2Volume: 0 - 100 % volume, 1% increments
Oxygen
• Oxygen (O2): 0 - 25.0% volume, 0.1% increments CO/H2S
• Carbon Monoxide (CO): 0 - 300 ppm, 1 ppm increments
• Carbon Monoxide (CO): 0 - 200 ppm, 1 ppm increments
• Carbon Monoxide (CO): 0 - 100 ppm, 1 ppm increments
• Hydrogen Sulfide (H2S): 0 - 100 ppm, 1 ppm increments
• Hydrogen Sulfide (H2S): 0 - 50 ppm, 0.1 ppm increments
Toxic
• Ammonia (NH3): 0 - 75.0 ppm, 0.1 ppm increments
• Ammonia (NH3): 0 - 100 ppm, 1 ppm increments
• Ammonia (NH3): 0 - 200 ppm, 1 ppm increments
• Ammonia (NH3): 0 - 500 ppm, 1 ppm increments
• Arsine (AsH3): 0 - 1.50 ppm, 0.01 ppm increments
•Chlorine(Cl
2): 0 - 3.00 ppm, 0.01 ppm increments
•Chlorine(Cl
2): 0 - 5.00 ppm, 0.01 ppm increments
•Chlorine(Cl
2): 0 - 10.0 ppm, 0.1 ppm increments
• Chlorine Dioxide (ClO2): 0 - 1.00 ppm, 0.01 ppm increments
• Chlorine Dioxide (ClO2): 0 - 3.00 ppm, 0.01 ppm increments
• Chlorine Dioxide (ClO2): 0 - 5.00 ppm, 0.01 ppm increments
• Hydrogen Cyanide (HCN): 0 - 15.0 ppm, 0.1 ppm increments
• Phosphine (PH3): 0 - 1.00 ppm, 0.01 ppm increments
• Sulfur Dioxide (SO2): 0 - 6.00 ppm, 0.01 ppm increments
• Sulfur Dioxide (SO2): 0 - 10.0 ppm, 0.01 ppm increments

8• Chapter 1: Introduction M2A-XL Transmitter Operator’s Manual
Alarm Settings
(Alarm 1/Alarm 2)*
Ammonia (0 - 75.0 ppm and 0 - 100 ppm): 12 ppm / 25 ppm
Ammonia (0 - 200 ppm): 25 ppm / 35 ppm
Ammonia (0 - 500 ppm): 35 ppm / 300 ppm
Arsine: 0.20 ppm / 0.50ppm
Carbon Dioxide (0 - 5,000 ppm): 2,500 ppm / 5,000 ppm
Carbon Dioxide (0 - 9,000 ppm): 2,000 ppm / 5,000 ppm
Carbon Dioxide (0 - 5.00%): 0.50% / 3.00%
Carbon Dioxide (0 - 50.0%): 50.0% / 50.0%
Carbon Dioxide (0 - 100%): 100% / 100%
Carbon Monoxide (all ranges): 25 ppm / 50 ppm
Chlorine (0 - 3.00 ppm): 0.50 ppm / 1.00 ppm
Chlorine (0 - 5.00 ppm): 0.50 ppm / 1.50 ppm
Chlorine (0 - 10.0 ppm): 1.0 ppm / 3.0 ppm
Chlorine Dioxide (0 - 1.00 ppm): 0.10 ppm / 0.30 ppm
Chlorine Dioxide (0 - 3.00 ppm): 0.30 ppm / 1.00 ppm
Chlorine Dioxide (0 - 5.00 ppm): 0.50 ppm / 1.00 ppm
Combustible Gas (%LEL): 10% LEL / 50% LEL
Combustible Gas (0-100%Volume): 100% / 100%
Hydrogen Cyanide: 5.0 ppm / 10.0 ppm
Hydrogen Sulfide (0 - 50 ppm): 5.0 ppm / 10.0 ppm
Hydrogen Sulfide (0 - 100 ppm): 10 ppm / 50 ppm
Methane (ppm): 5000 ppm / 8000 ppm
Methane (0-5.00%Volume): 0.5% / 2.5%
Oxygen: 19.5% (decreasing) / 23.5% (increasing)
Phosphine: 0.10 ppm / 0.30 ppm
Sulphur Dioxide (both ranges): 1.00 ppm / 2.00 ppm
Construction
(housing)
Explosion-proof Junction Box, NEMA 4X
Area Classification Explosion-proof for Class I, Groups B, C, and D (Combustible, CO2, CSA
Type CO and H2S, and CSA Type oxygen)
Sampling Method Diffusion
Input Power 10 - 30 VDC
Controls • Three push button switches
• Three magnetic switches for non-intrusive calibration
Weight 4.5 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
Table 1: M2A-XL Specifications

M2A-XL Transmitter Operator’s Manual Chapter 1: Introduction • 9
WARNING: When using the M2A-XL, you must follow the instructions and warnings in this
manual to assure proper and safe operation of the M2A-XL and to minimize the
risk of personal injury. Be sure to maintain and periodically calibrate the M2A-
XL as described in this manual.
Explosion Proof Non-Explosion
Proof
Operating
Temperature
Catalytic LEL/ppm -40°C to 75°C N/A
Oxygen -20°C to 45°C -20°C to 50°C
H2S -40°C to 40°C -40°C to 50°C
CO -5°C to 40°C -20°C to 50°C
Toxic (ESM-01) N/A -10°C to 40°C
Toxic (CT-7 Series) N/A -20°C to 40°C
Infrared Combustible -20°C to 50°C -40°C to 50°C
Infrared CO2-20°C to 50°C -40°C to 50°C
Accuracy
Catalytic Combustible Gas (LEL range):
± 5% of reading or ± 2% LEL (whichever is greater)
Catalytic CH4(ppm range):
± 5% of reading or ± 50 ppm (whichever is greater)**
IR Combustible Gas/IR CO2:
± 5% of reading or ± 2% of full scale (whichever is greater)
Oxygen:
± 0.5% O2
Hydrogen Sulfide:
± 5% of reading or ± 2 ppm H2S (whichever is greater)
Carbon Monoxide:
± 5% of reading or ± 5 ppm CO (whichever is greater)
Toxic Sensors (ESM-01 Type and CT-7 Series Type):
± 10% of reading or ± 5% of full scale (whichever is greater)
* These are RKI factory settings. See “Viewing & Changing M2A-XL Parameters” on page 47 to
change the alarm settings.
** Independent of zero drift
Table 1: M2A-XL Specifications

10 • Chapter 2: Description M2A-XL Transmitter Operator’s Manual
Chapter 2: Description
Overview
This chapter describes external and internal components of the M2A-XL Transmitter.
External Description
This section describes the junction box and all external components of the M2A-XL transmitter.
Figure 1: M2A-XL External Components
Junction Box
The M2A-XL’s cast aluminum junction box is dust and weather resistant. The junction box also
protects the M2A-XL and all connections made to it. Use the three 3/4 NPT conduit ports to
mount the detector to the junction box (factory installed in the bottom port) and connect wiring
from an external device (left port). The top port 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 port can be used for wiring.
WARNING: If the top conduit port is used for wiring, be sure to seal the threads to ensure
water does not enter the junction box. See “Wiring the M2A-XL Transmitter” on
page 30 for complete wiring instructions.
Junction Box Cover
Window
Magnetic
Wand
Mounting Hole (2x)
3/4 NPT Conduit Port, Plugged
Detector
(Catalytic LEL Detector Shown)
3/4 NPT
Conduit Port

M2A-XL Transmitter Operator’s Manual Chapter 2: Description • 11
Use the junction box’s two mounting holes to mount the M2A-XL 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.
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.
Gas Detector
The gas detector senses the target gas and is mounted in a 3/4 NPT conduit port on the right
bottom side of the M2A-XL. A variety of detectors may be used with the M2A-XL. See the
sections below for descriptions of each type of detector.
Catalytic Detectors
The catalytic detectors have a 1/2 NPT thread and require a 3/4 NPT x 1/2 NPT reducer to install
in the detector port.
The table below outlines the M2A-XL part numbers and replacement detector part numbers for
the catalytic detectors.
Table 2: Catalytic Detectors
Target Gas, Range M2A-XL Part
Number Detector Used
Combustible Gas, 0 - 100% LEL 65-2640RK 61-0140RK (Catalytic UL version)
65-2640RK-05 61-0140RK-05 (Catalytic CSA version)
Hydrogen, 0 - 100% LEL 65-2641RK NC-6205-01 (Catalytic UL version, hydrogen
specific)
65-2641RK-05 NC-6205-05 (Catalytic CSA version, hydrogen
specific)
Methane, 0 - 9000 ppm 65-2647RK 61-0140RKA (Catalytic UL version)
65-2647RK-05 61-0140RKA-05 (Catalytic CSA version)

12 • Chapter 2: Description M2A-XL Transmitter Operator’s Manual
Figure 2: Catalytic Sensors
Infrared (IR) Detectors
The IR combustible detectors are generally used instead of the catalytic combustible detectors in
applications where there may be catalyst poisons such as silicone present or where oxygen is not
present in the monitoring environment.
The table below outlines the M2A-XL part numbers and replacement detector part numbers for
the infrared (IR) detectors.
Table 3: Infrared (IR) Detectors
Target Gas, Range M2A-XL Part
Number Detector Used
CH4, 0 - 100% LEL 65-2649RK-CH4 61-0190RK-CH4 (UL)
65-2664RK-CH4 61-0197RK-CH4
CH4, 0 - 5.00% volume 65-2649RK-CH4-5 61-0190RK-CH4 (UL)
CH4, 0 - 100% volume 65-2658RK-CH4 61-0192RK-CH4 (UL)
65-2665RK-CH4 61-0199RK-CH4
CO2, 0 - 5,000 ppm 65-2660RK-02 61-0191RK-02 (UL)
65-2661RK-02 61-0198RK-02
CO2, 0 - 9,000 ppm 65-2660RK-01 61-0191RK-01 (UL)
65-2661RK-01 61-0198RK-01
CO2, 0 - 5% volume 65-2660RK-03 61-0191RK-03 (UL)
65-2661RK-03 61-0198RK-03
Detector PartNumbers
61-0140RK
61-0140RKA
NC-6205-01
UL Version
Detector Part Numbers
61-0140RK-05
61-0140RKA-05
NC-6205-05
CSA Version

M2A-XL Transmitter Operator’s Manual Chapter 2: Description • 13
Figure 3: Infrared (IR) Sensors
Oxygen Detectors
There are three types of oxygen detectors available: a non-explosion proof partial pressure type, a
non-explosion proof capillary type with a replaceable sensor, and an explosion proof (CSA)
capillary type with a replaceable sensor. The capillary type’s output is less susceptible to
variations in atmospheric pressure than the partial pressure type. The CSA type oxygen detector
(65-2514RK) and the non-explosion proof capillary type detector (65-2494RK) has a replaceable
plug-in sensor inside the detector housing. The entire oxygen detector must be removed if
replacement is required for the 65-2510RK.
CO2, 0 - 50% volume 65-2660RK-05 61-0191RK-05 (UL)
65-2661RK-05 61-0198RK-05
CO2, 0 - 100% volume 65-2660RK-10 61-0191RK-10 (UL)
65-2661RK-10 61-0198RK-10
HC, 0 - 100% LEL (cal. to propane) 65-2649RK-HC 61-0190RK-HC (UL)
65-2664RK-HC 61-0197RK-HC
Table 3: Infrared (IR) Detectors
Target Gas, Range M2A-XL Part
Number Detector Used
Detector Housing Body
Cap Gasket
Plug-In IR LEL Sensor
Detector Housing Cap
Non-XP, Replaceable-Sensor Type
Hydrophobic
Membrane
XP, Non-Replaceable-
Sensor Type
Detector PartNumbers
61-0197RK-CH4
61-0197RK-HC
61-0198RK-01
61-0198RK-02
61-0198RK-03
61-0198RK-05
61-0198RK-10
61-0199RK-CH4
Detector PartNumbers
61-0190RK-CH4
61-0190RK-HC
61-0191RK-01
61-0191RK-02
61-0191RK-03
61-0191RK-05
61-0191RK-10
61-0192RK-CH4
61-0192-HC

14 • Chapter 2: Description M2A-XL Transmitter Operator’s Manual
The table below outlines the M2A-XL part numbers and replacement detector part numbers for
the oxygen detectors.
Figure 4: Oxygen Detectors
CO and H2S Detectors
Both types of CO and H2S detectors (explosion-proof and non-explosion-proof) have replaceable
plug-in sensors inside the detector housing.
The CO detectors include a charcoal filter disk which is held onto the sensor with a rubber
retaining boot. The charcoal filter disk scrubs out interfering gases to which the CO sensor
responds such as H2S and certain hydrocarbons.
The 65-2428 and 65-2428-01 explosion-proof H2S detectors both include a rubber boot and a
spacer which help ensure that the sensor remains plugged into the detector housing body. The
only difference between the 65-2428 and the 65-2428-01 is that the sensor used in the 65-2428-01
is resistant to degradation caused by frequent exposure to low levels of H2S or occasional
exposure to high levels of H2S.
The 65-2495RK non-explosion-proof H2S detector includes an adhesive-backed gasket inside the
detector housing cap which helps ensure that the sensor remains plugged into the detector housing
body.
Table 4: Oxygen Detectors
Target Gas, Range M2A-XL Part
Number Detector Used
Oxygen, 0 - 25% 65-2643RK-05 65-2514RK (capillary, CSA)
65-2644RK 65-2510RK (partial pressure)
65-2666RK 65-2494RK (capillary)
Cap Gasket
Detector HousingBody
Detector
Housing Cap
Hydrophobic
Membrane
Detector
Housing Cap
Plug-In Oxygen
Sensor
Cap Gasket
Non-XP, Replaceable-SensorCapillary Type Non-XP, Partial
Pressure Type
Oxygen Sensor
Detector HousingBody
Flame
Arrestor
Guard
Detector PartNumber
65-2494RK Detector Part Number
65-2510RK
Detector PartNumber
65-2514RK
XP, Replaceable-Sensor CapillaryType

M2A-XL Transmitter Operator’s Manual Chapter 2: Description • 15
The table below outlines the M2A-XL part numbers and replacement detector part numbers for
the CO and H2S detectors.
Figure 5: H2S Detectors
Table 5: CO and H2S Detectors
Target Gas, Range M2A-XL Part
Number Detector Used
CO, 0 - 300 ppm 65-2646RK-05 65-2438 (CSA)
65-2663RK 65-2496RK
CO, 0 - 200 ppm 65-2646RK-05-02 65-2438-01
CO, 0 - 100 ppm 65-2646RK-05-01 65-2438-01
H2S, 0 - 100 ppm 65-2645RK-05 65-2428 (CSA)
65-2645-05-07 65-2428-01 (CSA)
65-2662RK 65-2495RK
Cap Gasket
Flame
Arrestor
Guard
H2S Plug-in Sensor
Spacer
Rubber Boot
Detector
Housing Cap
Non-XP Type
Detector
Housing Cap
Hydrophobic
Membrane
Cap Gasket
H2S Plug-in Sensor
Detector Housing Body
Detector Part Number
65-2495RK
Detector Part Numbers
65-2428
65-2428-01
Detector Housing Body
XP Type

16 • Chapter 2: Description M2A-XL Transmitter Operator’s Manual
Figure 6: CO Detectors
ESM-01 Detectors
The construction of the various ESM-01 detectors is similar. Each of the ESM-01 detectors has a
different replaceable plug-in sensor that protrudes through the detector housing cap. Although
ESM-01 detectors look the same except for the plug-in detector, the detector housing which
includes the detector socket and conditioning circuitry is specific to a sensor type. For example, a
detector housing from a Cl2detector cannot be used with an NH3detector. One of the two
detector wires is color coded for each specific detector type. The ESM-01 detectors include a
removable splashguard that screws onto the detector housing cap. When it is necessary to apply
gas to an ESM-01 detector, remove the splashguard to allow access to the sensor that protrudes
through the detector housing cap. You can then push the appropriate ESM-01 calibration cup onto
the sensor.
The table below outlines the M2A-XL part numbers and replacement detector part numbers for
the ESM-01 detectors.
Table 6: ESM-01 Detectors
Target Gas, Range M2A-XL Part
Number Detector Used
AsH3, 0 - 1.5 ppm 65-2648RK-ASH3 65-2300RK-ASH3
Cl2, 0 - 3 ppm 65-2648RK-CL2 65-2300RK-CL2
Cl2, 0 - 10 ppm 65-2648RK-CL-10 65-2300RK-CL-10
HCN, 0 - 15 ppm 65-2648RK-HCN 65-2300RK-HCN
NH3, 0 - 75 ppm 65-2648RK-NH3 65-2300RK-NH3
PH3, 0 - 1 ppm 65-2648RK-PH3 65-2300RK-PH3
SO2, 0 - 6 ppm 65-2648RK-SO2 65-2300RK-SO2
Detector
Housing Cap
Charcoal Filter
w/Rubber Boot
CO Plug-inSensor
Cap Gasket
Detector Housing Body
Cap Gasket
Hydrophobic
Membrane
CO Plug-inSensor
Flame
Arrestor
Guard
Detector
Housing Cap
Non-XP Type
Detector PartNumber
65-2496RK
Detector Housing Body
Rubber Boot w/
Charcoal Filter
XP Type
Detector PartNumber
65-2438
65-2438-01

M2A-XL Transmitter Operator’s Manual Chapter 2: Description • 17
Figure 7: ESM-01 Type Detector
CT-7 Series Detectors
The CT-7 Series detectors for Cl2, ClO2, HCn, and SO2have a replaceable plug-in sensor inside
the detector housing. An adhesive backed gasket inside the detector housing cap helps ensure that
the sensor remains plugged into the detector housing body.
The table below outlines the M2A-XL part numbers and replacement detector part numbers for
the CT-7 Series detectors.
Table 7: CT-7 Series Detectors
Tar g et Gas ,
Range
M2A-XL Part
Number Detector Used
Cl2, 0 - 3 ppm 65-2670-CL2-3 65-2302-CL2-3
Cl2, 0 - 5 ppm 65-2670-CL2-5 65-2302-CL2-5
Cl2, 0 - 10 ppm 65-2670-CL2-10 65-2302-CL2-10
ClO2, 0 - 1 ppm 65-2670-CLO2-1 65-2302-CLO2-1
ClO2, 0 - 3 ppm 65-2670-CLO2-3 65-2302-CLO2-3
ClO2, 0 - 5 ppm 65-2670-CLO2-5 65-2302-CLO2-5
HCN, 0 - 15.0 ppm 65-2670-HCN-15 65-2302-HCN-15
NH3, 0 - 75.0 ppm 65-2670-NH3-75 65-2302-NH3-75
NH3, 0 - 100 ppm 65-2670-NH3-1 65-2302-NH3-1
Splash Guard
(removable)
Cap Gasket
Detector Housing Body
(different for each detector type)
Sensor
(different for each detector type)
Detector Housing
Cap

18 • Chapter 2: Description M2A-XL Transmitter Operator’s Manual
Figure 8: CT-7 Series Detectors
NH3, 0 - 200 ppm 65-2670-NH3-2 65-2302-NH3-2
NH3, 0 - 500 ppm 65-2670-NH3-5 65-2302-NH3-5
SO2, 0 - 10 ppm 65-2670-SO2-10 65-2302-SO2-10
Table 7: CT-7 Series Detectors
Tar g et Gas ,
Range
M2A-XL Part
Number Detector Used
Hydrophobic Membrane
Plug-in Sensor
Detector
Housing Cap
Cap Gasket
Detector Housing Body
(different foreach detector type)

M2A-XL Transmitter Operator’s Manual Chapter 2: Description • 19
Internal Description
This section describes the internal components of the M2A-XL. The internal components of the
M2A-XL include the terminal PCB which provides for all the wiring connections to the M2A-XL
and the control PCB which displays the gas reading and has the control buttons.
Figure 9: M2A-XL 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 is 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-XL to a Modbus network. The terminal PCB also controls three relays: one fail and two
gas alarm.
NO
Control PCB
Terminal PCB
M2A-XL TRANSMITTER
Junction Box
3/4 NPT Conduit Opening
3/4 NPT Conduit
Opening for Wire Entry RKIINSTRUMENTS

20 • Chapter 2: Description M2A-XL Transmitter Operator’s Manual
Two columns of plug-in style terminal strips are used to make all wiring connections to the M2A-
XL. 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-XL. On the combustible and CO2versions of the M2A-
XL, a factory adjust pot just above the programming connector is used to set the detector current.
Figure 10: 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-XL 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-XL 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).
- S +
A B C
RS 485 PWR/SIG
R W G B
LEL
C NC NO
ALARM 1 C NC NO
ALARM 2
C NC NO FAIL
Modbus Terminal Strip
Ground Jumper
Programming Connector
(Factory Use)
Power/Signal Terminal Strip
Termination Jumper
Ribbon Cable Connector
Detector Current Adjust Pot
(Comb/CO2 Type Only, Factory Adjust)
Detector Terminal Strip
(Comb/CO2 Version Shown) Relay
Terminal
Strips