Emerson MRLDS-450 User manual

MRLDS-450 Refrigerant Gas Detection 
Installation and Operation Manual
026-1316 Rev 0

Emerson
1065 Big Shanty Road NW, Suite 100
Kennesaw, GA 30144 USA
770-425-2724 • www.emerson.com

Table of Contents • v
CONTENTS
1 INTRODUCTION .............................................................................................................................. 1
1.1. ABOUT THIS MANUAL....................................................................................................................... 1
1.2. ICONOGRAPHY .................................................................................................................................. 1
1.3. GENERAL SAFETY REQUIREMENTS................................................................................................... 2
1.4. SAFE CONNECTION OF ELECTRICAL DEVICES .................................................................................. 3
2 PRODUCT DESCRIPTION ............................................................................................................. 4
2.1. INTENDED USES/APPLICATIONS........................................................................................................ 4
2.2. MRLDS-450..................................................................................................................................... 4
2.2.1. MRLDS-450 Product Overview................................................................................................ 4
2.2.2. MRLDS-450 Design Features .................................................................................................. 5
2.2.3. MRLDS-450 Component Overview .......................................................................................... 6
3 INSTALLATION ............................................................................................................................... 7
3.1. GENERAL INFORMATION ................................................................................................................... 7
3.2. RESTRICTIONS ................................................................................................................................... 8
3.3. MECHANICAL INSTALLATION ........................................................................................................... 8
3.4. ELECTRICAL INSTALLATION ............................................................................................................. 8
3.4.1. Preparations............................................................................................................................. 8
3.4.2. Power and Signal Wiring ......................................................................................................... 9
3.4.3. Relay Wiring............................................................................................................................. 9
3.4.4. Modbus RTU RS-485 Interface .............................................................................................. 10
3.4.5. Conclusion.............................................................................................................................. 13
4 OPERATION.................................................................................................................................... 13
4.1. OVERVIEW OF NORMAL OPERATION .............................................................................................. 13
4.1.1. Applying Power and the Start-up Sequence ........................................................................... 13
4.1.2. Verifying Analog Signals........................................................................................................ 14
4.1.3. Verifying the Modbus Signal .................................................................................................. 14
4.1.4. Status Indication..................................................................................................................... 15
4.1.5. Switch Functions .................................................................................................................... 15
4.1.6. Reset System to Factory Default Settings............................................................................... 17
4.2. MRLDS-400 SERIES APPLICATION ................................................................................................ 17
4.2.1. Enable Bluetooth® Connection.............................................................................................. 17
4.2.2. Checking Status ...................................................................................................................... 18
4.2.3. Instrument Configuration ....................................................................................................... 19
5 CARE AND MAINTENANCE ....................................................................................................... 26
5.1. MAINTENANCE INTERVALS ............................................................................................................ 26
5.2. ADJUSTMENTS................................................................................................................................. 27
5.2.1. Introduction ............................................................................................................................ 27
5.2.2. General Calibration Procedure ............................................................................................. 27
5.2.3. Zero Adjustment ..................................................................................................................... 28
5.2.4. Span Adjustment ..................................................................................................................... 29

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5.2.5. System Bump Test .................................................................................................................. 30
5.3. SENSOR MAINTENANCE.................................................................................................................. 31
5.3.1. Replacing Sensor Module ...................................................................................................... 32
5.4. CLEANING THE INSTRUMENT.......................................................................................................... 33
6 ADDITIONAL INFORMATION................................................................................................... 34
6.1. SENSOR PRINCIPLE ......................................................................................................................... 34
6.1.1. Electrochemical Sensors........................................................................................................ 34
6.1.2. Catalytic Bead Sensors .......................................................................................................... 34
6.1.3. Semiconductor Sensors .......................................................................................................... 35
6.1.4. Infrared Sensors..................................................................................................................... 35
6.2. DISPOSING OF THE INSTRUMENT .................................................................................................... 36
6.2.1. Disposing of the Electrical and Electronic Equipment ......................................................... 36
6.2.2. Disposing of Sensors.............................................................................................................. 36
6.3. TECHNICAL SPECIFICATIONS .......................................................................................................... 37
6.3.1. General Specifications........................................................................................................... 37
7 ORDERING INFORMATION....................................................................................................... 39

About this Manual Introduction • 1
1 Introduction
1.1. About this Manual
Thank you for investing in an MRLDS-450 Gas Detector. To ensure operator safety
and the proper use of the gas detector, please read the contents of this manual for
important information about the operation and maintenance of the instrument.
IMPORTANT: Before installing this product, carefully read and strictly follow the
instructions in the manual.
1.2. Iconography
Table 1-1 - Icons
Alert Icon Description
Danger Imminently hazardous situation which, if not avoided,
will result in serious injury or death.
Warnin g Potentially hazardous situation which, if not avoided,
could result in serious injury or death.
Potential electrical shock hazard which, if not avoided,
could result in serious injury or death.
Caution Potentially hazardous situation which, if not avoided,
could result in physical injury or damage to the product
or environment. It may also be used to alert against
unsafe practices.
Important Additional information on how to use the product.

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1.3. General Safety Requirements
IMPORTANT: Before using this product, carefully read and strictly follow the instructions
in the manual. Ensure that all product documentation is retained and available to anyone
operating the instrument.
DANGER! This instrument is neither certified nor approved for operation in 
oxygen-enriched atmospheres. Failure to comply may result in personal injury or death.
DANGER! This instrument has not been designed to be intrinsically safe for use in areas
classified as being hazardous locations. For your safety, DO NOT use it in hazardous

(classified) locations.
WARNING! Use this product only for the purposes specified in this document and under
the conditions listed.
CAUTION! In the event of an alarm or over-range condition, the sensor must be 
re-calibrated to ensure continued accuracy.
CAUTION! This product must be re-calibrated if installed in a non-room condition 
environment (For example, temperature or humidity extremes).
CAUTION! The gas diffusion path can become occluded (moisture, dust, debris, frozen
condensation) over time resulting in reduced or complete lack of gas detection and

alarming function. Routine visual inspection of the gas detector and bump testing are 
suggested to ensure proper gas detection and alarm function.
CAUTION! Except for maintenance detailed in this manual, these products should only be
opened and/or serviced by authorized Emerson Technical Support personnel.

Failure to comply may void the warranty.
CAUTION! Operator assumes responsibility for complying with all laws, rules and 
regulations governing the use of this product.

CAUTION! Use only genuine Emerson parts and accessories. Failure to comply may 
impair the operation of the product and/or void the warranty.
CAUTION! Only operate the product within the framework of a risk-based alarm signaling
concepts.
WARNING! The gas diffusion path can become occluded (moisture, dust, debris, frozen
condensation) over time, resulting in reduced or complete lack of gas detection and 
alarming function. Routine visual inspection of the gas detector and bump testing are 
recommended to ensure proper gas detection and alarm function. For information on 
calibrating the sensor, refer to the “Care and Maintenance” section of this manual.
Safe Connection of Electrical Devices Introduction • 3
1.4. Safe Connection of Electrical Devices
WARNING! Before connecting this instrument to electrical devices not mentioned in this
manual, consult the manufacturer or a qualified professional. Failure to comply may result
in personal injury and/or damage to the product.

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2 Product Description
2.1. Intended Uses/Applications
MRLDS-450 Gas Detection Series instruments continuously monitor ambient air
(indoor or outdoor) for the following gas types:
• Refrigerants
• Oxygen
• Toxic and combustible gases
The MRLDS-450 refrigerant gas detector is designed for use in refrigeration
applications and with the integrated audio-visual alarm indication, can be operated
as a stand-alone unit (with additional local alarm signaling as required), or it may be
connected to a facility's building management system (BMS). It enables compliance
with refrigerant safety codes (ASHRAE 15 and EN378) and alarms to alert
personnel in the event of a refrigerant leak.
DANGER! This instrument is neither certified nor approved for operation in 
oxygen-enriched atmospheres. Failure to comply may result in EXPLOSION.
DANGER! This instrument has not been designed to be intrinsically safe for use in areas
classified as being hazardous locations. For your safety, DO NOT use it in hazardous 
(classified) locations.
2.2. MRLDS-450
2.2.1. MRLDS-450 Product Overview
The Emerson MRLDS-450 continuously monitors indoor or outdoor ambient air for
the following gases:
• Refrigerants
• Oxygen
• Toxic and combustible gases

MRLDS-450 Product Description • 5
With the integrated Modbus communication, analog output and relays, the
instrument can be operated as a stand-alone unit or as a third-party device capable
of accepting digital and/or analog outputs from the gas detectors, such as a Building
Management System (BMS) or a Supervisory Controller. The instrument is
designed to be installed in non-classified, non-hazardous, permanent locations.
Figure 2-1 - MRLDS-450
2.2.2. MRLDS-450 Design Features
• Transmitter: IP66 rated ABS enclosure
• Power options:
• 24VAC
• 19.5 to 28.5VDC
• Diagnostic/Status LED (3 color): Green, Orange, and Red
• Configurable output signal options
• 3× Relays (high alarm/low alarm/fault)
• 1× Analog Output (4 to 20mA, 0 to 5V
, 0 to 10V, 1 to 5V, 2 to 10V)
• Digital Output (Modbus RTU signal)
Bluetooth communication allows for full instrument configuration, initiation of
calibration, bump test and functional test mode, and viewing of status information
via the corresponding MRLDS-450 iOS/Android app.
Non-intrusive magnetic wand can be used to initiate calibration of the device.

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2.2.3. MRLDS-450 Component Overview
Figure 2-2 - MRLDS-450 Component Locations
Table 2-1 - MRLDS-450 Component Descriptions
#Component Description
1M16 Cable Glands (x6)
2Rubber Gasket
3Internal Alarm Buzzer
4Power Connections (x2)
5Digital Connection (Modbus)
6Analog Connection
7Tactile Switch #1
8Ribbon Cable Connection (To Sensor)
9Tactile Switch #2
10 Relay 3 Connection (FAULT)
11 Relay 2 Connection (HIGH)
12 Relay 1 Connection (LOW)
13 Magnetic (Mag) Switch #1
14 Magnetic (Mag) Switch #2
15 M20 Cable Glands (x2)

General Information Installation • 7
3 Installation
CAUTION! The manufacturer of this product requires that a bump test or calibration be
performed following installation to verify instrument functionality.
3.1. General Information
Every detail of installation site selection is critical to ensure overall system
performance and effectiveness. Strict compliance and considerable thought must be
given to every detail of the installation process, including, but not limited to the
following:
• Regulations as well as local, state, and national codes that govern the installation of
gas monitoring equipment.
• Electrical codes that govern the routing and connection of electrical power and signal
cables to gas monitoring equipment.
• The full range of environmental conditions to which the instruments will be exposed.
• The physical characteristics of the gas or vapor to be detected.
• The specifics of the application (For example, possible leaks, air movement/draft,
etc.)
• The degree of accessibility required for maintenance purposes.
• The types of optional equipment and accessories that will be used with the system.
• Any limiting factors or regulations that would affect system performance or 
installations.
• Wiring details, including:
• The MRLDS-450 enclosure provides the following cable gland openings:
• 2×, M20, supports 10-14mm cable outer diameter
• 6×, M16, supports 4-8mm cable outer diameter
• Secondary circuit must be supplied from an isolating source.
• The wiring for the relays must be selected and fused according to the rated 
voltages, currents, and environmental conditions.
• If stranded conductions are used, ferrule should be used.
• To comply with RFI immunity regulations, it is necessary to ground the shield of
the communications cable at the PLC, GDA controller, front-end controller or
Building Management System (For example, the chassis, the ground bus-bar,
etc.).

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3.2. Restrictions
The installation location must have appropriate supply power available for the
instrument (For example, 19.5 to 28.5VDC or 24VAC). This ultimately determines
the distance the instrument can be mounted from the controller or power supply.
3.3. Mechanical Installation
WARNING! DO NOT allow the lid/sensor to hang from the ribbon cable. Failure to 
comply may result in damage to the product.
1. Using the provided hardware, securely mount the MRLDS-450 Gas Detector 
according to the product dimensions, maximum wiring lengths and following 
considerations:
a. Environment: the full range of environmental conditions when selecting a 
location.
b. Application: the specifics of the application (possible leaks, air movement/draft,
etc.) when selecting a location.
c. Accessibility: the degree of accessibility required for maintenance purposes
when selecting a location.
d. Target Gas: the specific gravity of the target gas when selecting the height of the
instrument.
2. Using a 5/32” (4mm) hex key/allen wrench (not included) remove the lid and 
disconnect the ribbon cable from the base.
3. Set the lid and rubber gasket aside to be reinstalled later.
3.4. Electrical Installation
3.4.1. Preparations
IMPORTANT: If analog output is configured for 4 to 20mA output, ensure that the current
loop is connected to a sinking current loop monitor before powering on the instrument.
Otherwise, a fault may be displayed indicating an open loop condition. If analog output is
unused, ensure it is configured as a voltage output (default: 1-5V) to prevent an open loop
fault condition. The analog output is designed as sourcing.
WARNING! Ensure wiring for relays and connections for sensor(s) are made before 
applying power.

CAUTION! This product uses semiconductors which can be damaged by electrostatic 
discharge (ESD). When handling the printed circuit boards (PCBs), observe proper ESD
precautions so that the electronics are not damaged.
Electrical Installation Installation • 9
3.4.2. Power and Signal Wiring
The product comes with cable glands and plugs pre-installed. The power entry cable
gland is without a gland plug. Use the appropriate cable glands to insert and connect
the wires for power and signal to the appropriate terminals as indicated in the figure
and wiring table that follow. The PCB terminal blocks are a pluggable type and may
be removed to aid termination.
IMPORTANT:
• For 24VAC installations sharing a transformer in a daisy-chain configuration, neutral
polarity must be maintained for all instruments.
• 24VAC power polarity must not be reversed.
• For a more robust system, a dedicated transformer for each MRLDS is recommended to
prevent damage caused by wiring errors.
• Fasten terminal screws.
Table 3-1 - Power and Signal Wiring
Power Description Label Wiring Termination
Power
24VDC/VAC IN 24V IN: - 24VDC/VAC neutral/ground
24V IN: + 24VAC neutral
24VDC/VAC OUT
(power daisy chain
terminal)
24V OUT: - 24VDC/VAC neutral/ground
24V OUT: + 24VAC neutral
Digital Output MODBUS Network
Communications
MODBUS: B RS-485 “B” (inverted)
MODBUS: A RS-485 “A” (non-inverted)
MODBUS: GND RS-485 GND
MODBUS: SH RS-485 Shield
Voltage or Current ANALOG: - Analog output ground
Analog
Output Output ANALOG: + Analog output signal (+)
3.4.3. Relay Wiring
WARNING! Relays are rated for 0 to 30V AC/DC. DO NOT apply main power onto these
relays.

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Using appropriate cable glands, connect the wires for relay 1, relay 2, and relay 3 to
the terminals as indicated in Table 3-2.
Table 3-2 - Relay Wiring Configuration
Relay Function
1Low Alarm
2High Alarm
3Fault Alarm
When configured according to the factory default settings, the relays are 
de-energized during normal operation (not fail-safe). Fail-safe mode can be
configured. When configured for Failsafe operation, relays are energized during
normal operation. Failsafe operation ensures relays are triggered in cases of power
failure at the instrument. In Failsafe operation, normally open and normally closed
terminals are reversed as indicated in Table 3-3
Table 3-3 - Relay Wiring Terminal Configuration
Terminal Normal Operation Failsafe Operation
NC Normally Closed Normally Open
COM Common Common
NO Normally Open Normally Closed
3.4.4. Modbus RTU RS-485 Interface
For the Modbus RS-485 network use a 16 to 24 AWG (0.5 to 1mm2) 3-core, 
2 twisted pair + ground, shielded cable with 120Ω characteristic impedance.
IMPORTANT: Recommended: Belden 3105A (or equivalent).
The Modbus address, baud rate, stop bit, parity and slave termination is configured
through the setup menu. No jumpers or hardware switch settings are required.
Ensure that the communication parameters within the network, including the BMS,
are configured identically.
To ensure optimal performance of the Modbus network ensure the following
guidelines are implemented:
• Ensure instruments are configured in a single bus topology, connecting multiple buses in 
parallel or branching multiple units from the main bus, may introduce impedance mismatches,
reflections and/or signal distortions.
• Avoid long stubs when connecting instruments to the bus, stubs should be less than one (1)
meter in length.

Electrical Installation Installation • 11
• Ensure A/B signal polarity is maintained throughout RS-485 network.
• Connect cable shield drain to physical earth or ground at the controller only.
• Ensure cable shield integrity is maintained throughout RS-485 network.
For Modbus end-of-line termination, use 150Ω ohm resistor or termination block 
P/N 537-2711. Do not use MRLDS 120Ωohm on-board termination with Site

Supervisor or E2.
Site Supervisor Setup - Device and COMM
Figure 3-1 - Site Supervisor Network Setup

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E2 Setup - Device and COMM
Figure 3-2 - E2 Network Setup

Overview of Normal Operation Operation • 13
3.4.5. Conclusion
After all wiring is completed, power the transmitter and confirm operation, and then
prepare to seal the enclosure.
Align the enclosure gasket (primary transmitter and remote sensor if equipped),
replace the lid, and tighten the six (6) screws. Tightening torque should be limited to
tightening by hand, and should be uniform in pattern.
4Operation
4.1. Overview of Normal Operation
CAUTION! Before leaving the instrument for normal operation, check the configuration
for proper settings and check calibration.
4.1.1. Applying Power and the Start-up Sequence
After applying power, the instrument will go through a start-up sequence
(initialization, audible/visual test and self-test sequence). After the start-up sequence
completes, the instrument will enter a warm-up period to allow the sensor element
to stabilize before reporting a valid output.
Table 4-1 - Instrument Start-up Sequence
Step Description
1Switch power on.
2
Observe start-up sequence and warm-up phase:
• Green LED will blink at 0.5 Hz for about five (5) minutes
• Modbus flag for warm-up is set
•Buzzer is off
• Relay state is “no alarm”
• Gas reading invalid
3
Observe normal operation:
• Green LED is steady on
• Modbus flag for warm-up is cleared
•Buzzer is off
• Relay state is “no alarm”
• Gas reading valid

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4.1.2. Verifying Analog Signals
The MRLDS-450 gas detector features a single configurable analog output. During
normal operation, the analog output of the instrument is proportional to the detected
gas concentration and can be selected from the following:
• 1 to 5V (Default)
• 0 to 5V
• 2 to 10V
• 0 to 10V
• 4 to 20mA
The MRLDS-450 Gas Detector uses different voltage/current values to indicate
various modes of operation. In normal operation the relative gas concentration
output is indicated by the analog output level. Output level is proportional to the gas
level as shown in Table 4-2:
Table 4-2 - Gas Concentration Levels
Gas Concentration 1-5V 0-5V 2-10V 0-10V 4-20mA
0% 1V 0V 2V 0V 4mA
50% 3V 2.5V 6V 5V 12mA
100% 5V 5V 10V 10V 20mA
The instrument may also enter several special states, these are indicated by the
specific analog output levels indicated in Table 4-3:
Table 4-3 - Analog Output Levels
Mode of Operation 1-5V 0-5V 2-10V 0-10V 4-20mA
Instrument Fault ≤ 0.3V N/A ≤ 0.6V N/A ≤ 1.2mA
Offline Mode/Maintenance 0.75V N/A 1.5V N/A 3mA
Drift below zero 0.95V N/A 1.9V N/A 3.8mA
Normal operation 1-5V 0-5V 2-10V 0-10V 4-20mA
Measuring range exceeded 5.12V 5.12V 10.25V 10.25V 20.5mA
Fault on analog interface > 5.25V > 5.25V > 10.5V > 10.5V > 21mA
4.1.3. Verifying the Modbus Signal
The MRLDS-450 Gas Detector provides a Modbus RTU digital interface. All status
messages and most parameters that can be accessed and/or configured through the
Bluetooth® interface can also be accessed and/or configured via RS485 for Modbus
RTU.

Overview of Normal Operation Operation • 15
4.1.4. Status Indication
The MRLDS-450 gas detections provide external indication of its current
operational state via audible and visual feedback. Visual indication of the instrument
status is provided by a single tri-color LED (Green/Red/Orange). MRLDS-450 gas
detection instruments also provide relays outputs. Instrument states and
corresponding outputs are shown in Table 4-4.
Table 4-4 - Status Indicators
State LED Buzzer Relay 1
(LOW)
Relay 2
(HIGH)
Relay 3
(Fault)
Warm-up OFF OFF OFF
Normal OFF OFF OFF
Low Alarm ON OFF OFF
High Alarm ON ON OFF
Offline OFF OFF OFF
Fault OFF OFF ON
Negative Gas Fault OFF OFF ON
Zero Cal. Fault OFF OFF OFF
Span Cal. Fault OFF OFF OFF
4.1.5. Switch Functions
User interaction with the MRLDS-450 gas detector is accomplished through the use
of two magnetic switches located on the bottom of each unit. To actuate a magnetic
switch, apply the supplied magnetic wand to the relevant switch location as shown
in Figure 4-1.

Figure 4-1 - Magnetic Switches
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Switch locations above are referred to in this document as MAG#1 and MAG#2.
Depending on the duration the switch is held, a short “tap” or long “hold” will be
detected.
• To carry out a tap function, tap the relevant switch location for one (1) second, until a
single “chirp” is heard and remove the wand to confirm a “tap.”
• To carry out a hold function, do not remove the magnetic wand after the first “chirp”
but continue to hold for more than five (5) seconds, until a double “chirp” is heard,
and remove wand to confirm a “hold.” If either switch is held for more than 30 
seconds, a stuck switch fault will be indicated.
• To interact with the instrument without use of the magnetic wand, two internal push
button tactile switches may be used. Remove the lid without removing the ribbon
cable to access. Internal switches TACT#1 and TACT#2 mirror the functions of
MAG#1 and MAG#2.
The function of each switch depends on the current state of the instrument. Refer to
Table 4-5 for switch functions in each instrument state.