Emerson Dixell GDS41M Wiring diagram

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GDS41M –GDS66M
GDI41M –GDI66M

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INDEX
1. GENERAL WARNING.................................................................................3
1.1 PRODUCT DISPOSAL WEE................................................................................................ 4
1.2 PRODUCT NOTICE ............................................................................................................. 4
1.3 TECHNICIAN USE ONLY..................................................................................................... 4
2. GENERAL INFORMATION.........................................................................5
2.1 TYPICAL USE...................................................................................................................... 6
3. GENERAL INSTALLATION GUIDELINES .................................................6
3.1 MAIN RECCOMANDATIONS:.............................................................................................. 6
3.2 PLACEMENT ....................................................................................................................... 7
3.2.1 MACHINERY ROOMS.......................................................................................................... 7
3.2.1.1 POSITIONING HEIGHT .......................................................................................... 8
3.2.2 REFRIGERANT SPACES .................................................................................................... 8
3.2.3 CHILLERS............................................................................................................................ 8
3.2.4 AIR CONDITIONING (DIRECT SYSTEM VRF/VRV)................................................................. 9
3.2.5 REMOTE SENSOR HEAD INSTALLATION.......................................................................... 9
4. INSTALLATION.........................................................................................10
4.1 WIRING AND SETTINGS....................................................................................................12
4.2 OPERATION AND STABILIZATION....................................................................................12
4.3 CONFIGURATION ..............................................................................................................13
4.4 ADJUSTING THE ALARM SET POINT................................................................................13
4.5 CALIBRATION ....................................................................................................................14
4.6 HOUSING DIMENSIONS ....................................................................................................15
5. TROUBLESHOOTING ..............................................................................16
6. MODBUS COMMUNICATION ..................................................................16
6.1 COMMUNICATION SETTINGS...........................................................................................16
6.2 WIRING AND ADDRESSING ..............................................................................................17
6.3 BAUD RATE........................................................................................................................18
6.4 ANALOG INPUT REGISTERS.............................................................................................18
6.5 ANALOG OUTPUT HOLDING REGISTERS........................................................................20
6.6 INPUT STATUS FLAGS......................................................................................................21
6.7 OUTPUT STATUS FLAGS ..................................................................................................22
7. MODBUS FLOW CHARTS .......................................................................22
8. TECHNICAL SPECIFICATIONS ...............................................................27

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1. GENERAL WARNING
Symbol warns the user about the presence of non-insulated "dangerous voltage" inside the product
area, which may cause electric shock.
Symbol warns the user about the presence of important operating and maintenance (assistance)
instructions found in the documentation attached to the device.
Dixell Srl reserves the right to modify this manual without prior notice. The documentation can be downloaded
from www.dixell.com even prior to purchase.
This manual forms part of the product and must always be kept near the device for easy and quick reference.
The device cannot be used as a safety device. Verifythe limits of application before using the device.
Verify that the power supply voltage is correct before connecting the device. Do not expose it to water or
humidity. Use the controller only within the operating limits, avoiding sudden temperature changes and high
atmospheric humidity, which may result in the formation of condensate. Warning: disconnect all the electric
connections before performing maintenance. The device must not be opened.
The customer shall bear full responsibility and risk for product configuration in order to achieve the results
pertaining to installation and/or final equipment/system.
Upon the customer's request and following a specific agreement, Dixell s.r.l. may be present during the start-
up of the final machine/application, as a consultant, however, under no circumstances can the company be
held responsible for the correct operation of the final equipment/system.
Since Dixell products form part of a very high level of technology, a
qualification/configuration/programming/commissioning stage is required to use them as best as possible.
Otherwise, these products may malfunction and Dixell cannot be held responsible. The product must not be
used in any way that differs from that stipulated in the documentation.
The device must never be hand-held while being used.
It is good practice to bear the following in mind for all Dixell products:
•Prevent the electronic circuits from getting wet as contact made with water, humidity or any other type of
liquid can damage them. Comply with the temperature and humidity limits specified in the manual in order
to store the product correctly.
•The device must not be installed in particularly hot environments as high temperatures can damage it
(electronic circuits and/or plastic components forming part of the casing). Comply with the temperature
and humidity limits specified in the manual in order to store the product correctly.
•Prevent the device from being dropped, knocked or shaken as either can cause irreparable damage.
•Do not clean the device with corrosive chemical products, solvents or aggressive detergents.
•The device must not be used in applications that differ from that specified in the following material.
Dixell Srl reserves the right to vary the composition of its products without prior notice to the customer,
ensuring the identical and unchanged features of the same.

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1.1 PRODUCT DISPOSAL WEE
With reference to Directive 2002/96/EC of the European Parliament and of the Council of 27 January 2003 and to
the relative national legislation, please note that:
There lies the obligation not to dispose of electrical and electronic waste as municipal waste but
to separate the waste.
Public or private collection points must be used for disposal, in accordance with local laws.
Furthermore, at the end of the product's life, it is also possible to return this to the retailer when a
new purchase is made.
This equipment may contain hazardous substances. Improper use or incorrect disposal can have
adverse effects on human health and the environment.
The symbol shown on the product or the package indicates that the product was placed on the
market after 13th August 2005 and must be disposed of as separated waste.
Should the product be disposed of incorrectly, sanctions may be applied as stipulated in
applicable local regulations regarding waste disposal.
1.2 PRODUCT NOTICE
COPYRIGHTS: this manual is subject to copyright protection; all rights are reserved under international and
domestic copyright laws.
This manual may not be copied or translated, in whole or in part, in any manner or format, without the written
permission of DIXELL S.r.l.
All software utilized and/or distributed by producer is subject to copyright protection. All rights are reserved.
No party may use or copy such software in any manner or format, except to the extent that producer grants them a
license to do so.
If this software is being loaded onto more than one computer, extra software licenses must be purchased.
1.3 TECHNICIAN USE ONLY
This unit must be installed by a suitably qualified technician who will install this unit in accordance with these
instructions and the standards in their particular industry/country.
Operators of the unit should be aware of the regulations and standards in their industry/country for the operation of
this unit. These notes are only intended as a guide and the manufacturer bears no responsibility for the installation
or operation of this unit.
Failure to install and operate the unit in accordance with these instructions and with industry guidelines may cause
serious injury including death and the manufacturer will not be held responsible in this regard.

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2. GENERAL INFORMATION
The GD product range is a state-of-the-art fixed gas detector which can detect a wide range of
different gases.
This kind of gas sensors are available in two different configurations in relation to the type of
sensing element:
GDS Range, with SEMICONDUCTOR sensor
GDI Range, with INFRARED sensor
Below the different type of boards:
GDS (Semiconductor)
GDI (Infrared)
The GD gas sensors are available in two different boxes, according to the desired degree of
protection (IP) and in relation of the specific installation:
IP41 Housing
IP66 Housing
The IP66 Housing is also available, with different order code, with the remote sensor.
NOTE: The GDS and GDI standard sensors without on board Modbus communication have
different boards, please see the dedicated manual for these devices.

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2.1 TYPICAL USE
The GDS and GDI Gas Sensors can be used in new buildings/areas that require continuous
monitoring with high tech gas sensor transmitters or to add gas detection solutions to an existing
system.
It’s possible to use the Gas Detectors in different modes:
Stand alone with direct control
With dedicated controller Dixell XHL210
With remote controller Dixell XWEB
Into Building Management Systems (BMS)
Typical detection applications include the detection of:
Refrigerant gases
Combustible gases (into refrigeration or HVAC systems)
Toxic gases and/or volatile organic compounds (into refrigeration or HVAC
systems)
3. GENERAL INSTALLATION GUIDELINES
3.1 MAIN RECCOMANDATIONS:
WARNING: Explosion hazard!
Do not mount the GDS or GDI Sensors in an area that may contain flammable
liquids (XE “Flamable Liquids”), vapors, or aerosols. Operation of any electrical
equipment in such an environment constitutes a safety hazard (XE “safety”).
CAUTION: The GDS and GDI contain sensitive electronic components (XE “Electronic
components”) that can be easily damaged. Do not touch nor disturb any of these
components.
NOTES:
The mounting location (XE “Mounting location”) of the monitor should allow it to be easily
accessible for visual monitoring and servicing.
The monitor must be connected by a marked, suitably located and easily reached switch
or circuit-breaker as means of disconnection.
Connect monitor power and signaling terminals using wiring that complies with local
electrical codes or regulations for the intended application.
This instrument can be equipped with a semiconductor sensor for the detection of
refrigerant, combustible and VOC gases. Semiconductor sensors are not gas specific
and respond to a variety of other gases including propane exhaust, cleaners, and
solvents.
Changes in temperature and humidity may also affect the sensor’s performance.

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3.2 PLACEMENT
Sensors must be located within the appropriate wire lengths from the central control unit (if used).
In all cases the sensor supplied is designed for maximum sensitivity to a particular gas.
However, in certain circumstances false alarms may be caused by the occasional presence of
sufficiently high concentrations of other gaseous impurities.
Examples of situations where such abnormalities may arise include the following:
Plant room maintenance activity involving solvent or paint fumes or refrigerant leaks.
Accidental gas migration in fruit ripening/storage facilities (bananas - ethylene, apples -
carbon dioxide).
Heavy localized exhaust fumes (carbon monoxide, dioxide, propane) from engine-driven
forklifts in confined spaces or close to sensors.
Dixell recommends setting the alarm delay to minimize false alarms.
Note: The Gas Sensor should be installed plumb and level and securely fastened to a rigid
mounting surface.
3.2.1 MACHINERY ROOMS
There is no absolute rule in determining the number of sensors and their locations. However, a
number of simple guidelines will help to make a decision. Sensors monitor a point as opposed to
an area. If the gas leak doesn’t reach the sensor then no alarm will be triggered. Therefore, it is
extremely important to carefully select the sensor location. Also consider ease of access for
maintenance.
The size and nature of the site will help to decide which method is the most appropriate to use.
Locations requiring the most protection in a machinery or plant room would be around
compressors, pressurized storage vessels, refrigerant cylinders or storage rooms or pipelines.
The most common leak sources are valves, gauges, flanges, joints (brazed or mechanical), filling
or draining connections, etc.
When mechanical or natural ventilation is present, mount a sensor in the airflow.
In machinery rooms where there is no discernable or strong airflow then options are:
oPoint Detection, where sensors are located as near as possible to the most
likely sources of leakage, such as the compressor, expansion valves,
mechanical joints or cable duct trenches.
oPerimeter Detection, where sensors completely surround the area or
equipment.
Sensors should be positioned just far enough back from any high-pressure parts to allow gas
clouds to form and be detected. Otherwise, a gas leak might pass by in a high-speed jet and not
be detected by the sensor.
Make sure that pits, stairwells and trenches are monitored since they may fill with stagnant
pockets of gas.
If a pressure relief vent (PRV) pipe is fitted to the system, it may be a requirement to mount a
sensor to monitor this vent pipe. It could be positioned about 2 m (6 feet) above the PRV to allow
gas clouds to form.
For racks or chillers pre-fitted with refrigerant sensors, these should be mounted so as to monitor
the compressors. If extract ducts are fitted the airflow in the duct may be monitored.

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3.2.1.1 POSITIONING HEIGHT
For heavier-than-air gases such as halocarbon and hydrocarbon refrigerants such as
R404A, propane, and butane sensors should be located near ground level.
With similar density or miscible gases (e.g. CO2), sensors should be mounted about
head high (about 1.5 m).
For lighter-than-air gas the sensor needs to be located above the equipment to be
monitored on a bracket or high on a wall within 300 mm (12 in) of (or on) the ceiling –
provided there is no possibility of a thermal layer trapped under the ceiling preventing
gas from reaching the sensor.
Note: At very low temperatures (e.g., refrigerated cold store), some gases could become heavier
than air.
3.2.2 REFRIGERANT SPACES
In refrigerated spaces, sensors should be located in the return airflow to the evaporators on a
sidewall (below head-high is preferred), or on the ceiling, not directly in front of an evaporator.
In large rooms with multiple evaporators, sensors should be mounted on the central line between 2
adjacent evaporators, as turbulence will result in airflows mixing.
3.2.3 CHILLERS
In the case of small water- or air-cooled enclosed chiller units mount the sensor so as to monitor
airflow to the extract fans.
With larger models also place a sensor inside the enclosure under or adjacent to the compressors.
In the case of outdoor units:
For enclosed air-cooled chillers or the outdoor unit for variable refrigerant volume and
variable refrigerant flow (VRV/VRF) systems, mount the sensor so as to monitor airflow
to the extract fan.
With large units also place a sensor inside the enclosure under or adjacent to the
compressors.
In the case of non-enclosed outdoor units:
If there is an enclosed machinery section locate a sensor there.
In the case of units with enclosed compressors, mount sensors in the enclosures.
Where you have protective or acoustic panels mount the sensor low down under the
compressors where it is protected by the panels.
With air-cooled chillers or air-cooled condensers with non-enclosed condenser sections
it is difficult to effectively monitor leaks in the coil sections. With some designs it will be
possible using an airflow sensor to monitor airflow to the start–up fans in the front or rear
sections.
If there is a possibility of refrigerant leaks into a duct or air-handling unit install a sensor
to monitor the airflow.
Weatherproof sensors should be used for unprotected outdoor applications.

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3.2.4 AIR CONDITIONING (Direct System VRF/VRV)
For compliance with EN378, at least one detector shall be installed in each occupied space being
considered and the location of detectors shall be chosen in relation to the refrigerant and they shall
be located where the refrigerant from the leak will collect.
In this case refrigerants are heavier than air and detectors should have their sensors mounted low,
e.g., at less than bed height in the case of an hotel or other similar Category Class A spaces.
Ceilings or other voids if not sealed are part of the occupied space.
Do Mount In-Room Sensors
Don’t Mount Sensors
… at less than the normal heights of the
occupants.
E.g., in a hotel room this is less than bed
height (between 200 and 500 mm off the
floor).
…under mirrors.
… away from drafts and heat sources like
radiators, etc.
…at vanity units.
… to avoid sources of steam.
…in or near bathrooms.
Monitoring ceiling voids in a hotel room would not strictly comply with EN378
3.2.5 REMOTE SENSOR HEAD INSTALLATION
The remote sensor is mounted in an electrical back box (44 mm) deep to which the vented
faceplate is fitted.
Remove the connector from the sensor PCB to feed the cable through the housing.
Immediately refit the connector to the sensor board in the back of the box.
The GDS/GDI and remote sensor must be kept together as they are calibrated together
and are a matched pair.
To clean, the faceplate should be lightly dusted.
IMPORTANT: Do not spray the device with cleaning or polishing aerosols
To avoid component mix-up, do not remove sensor boards from multiple units at the
same time. Alternatively, label them, or match the serial number on the main PCB and
the remote sensor PCB when reinstalling.

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4. INSTALLATION
GDS Gas Sensor (Semiconductor)

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GDI Gas Sensor (Infrared)

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4.1 WIRING AND SETTINGS
ITEMS
DESCRIPTION
Enclosure Access
To open the standard sensor enclosure, turn the cable clamp
1/2 turn counter-clockwise to loosen the internal gland nut,
depress the clip on top of the enclosure and open.
Reverse to close.
(Note: For the IP66 enclosure, use the four bolts on the front
cover.)
Power
12-24V AC/DC, connect at positions 0V and +V at connector
block CN1.
For AC: Jumper A is on, D is off. (See Figures)
For DC: Jumper A is off, D is on. (See Figures)
Default factory setting is DC.
Use 2 wires, typically 1 mm2(minimum).
Output
Connect two wires to terminal block CN2 positions 0V and V or I
for voltage or current, respectively:
Connect 4-20mA at CN2 positions 0V and I
Connect voltage output at CN2 positions 0V and V
Not use a common ground for these connections.
Relay Set Point
P1 sets the trip point for the relay and audible alarm using the 0-
5V scale (measure at test points 0V and alarm test point REF1).
Default factory setting is 50% of the range.
Time Delay
A time delay for the operation of the relay and audible alarm can
be selected using jumpers JP5 and JP6.
Default factory setting is zero.
Audible Alarm
The audible alarm can be disabled using jumper JP3.
Default factory setting is enabled.
4.2 OPERATION AND STABILIZATION
On powering up, the Gas Sensor will sense for the presence of gas after an initial warm-up delay
of 5 minutes. The green LED will flash at 1 second intervals during the warm-up.
In an alarm condition:
•green LED stays on and the red LED is on
•audible alarm operates (if not disabled and after delay, if set).
•relay output activates (after a delay, if set)
•V and I output changes proportionally with gas concentration.
In a fault condition:
•green LED will be off and the red LED will be on
•voltage/current fault output will activate:
o2mA on the 4-20mA output
o0.5V on the 1-5V output
o1.0V on the 2-10V output.
The typical time to stabilize the Gas Sensors is 1÷3 minutes.

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On power up, the semiconductors output over the + max scale (i.e., > 5V), move towards zero as
they stabilize.
If sensors have been in long-term storage or the detectors have been turned off for a long period,
stabilization is much slower.
However, within 1-2 hours sensors should have dropped below the alarm level and be operational.
You can monitor progress exactly by monitoring the 0-10V output. When the output settles around
zero the sensor is stabilized.
In exceptional circumstances the process can take up to 24 hours or more.
4.3 CONFIGURATION
FUNCTION
DESCRIPTION
Time delay
Available on the audible alarm and relay to avoid false alarms.
This is set with jumpers. The default delay is 0 minutes. You
may wish to set to 15 minutes during start up.
See figures above for setting the jumpers.
Audible Alarm
The units have an internal audible alarm.
You can disable this by jumper, but the default setting is
“enabled” in compliance withEN378.
See figures above for setting the jumpers.
Output
Decide which output is required: 4-20mA, 1-5V, 0-10V, relay
outputs, etc.
See figures above for setting the jumpers.
4.4 ADJUSTING THE ALARM SET POINT
This process is the same for all versions, using
test points as the below specifications.
For the alarm adjustement:
Locate Pot P1 and use it to adjust the set
point at which the relay activates.
Monitor the output between test points 0
(negative) and TP1 (positive) until the
correct setting is reached. See example
below.
Example:
Gas Sensor with probe range 0-1000 ppm
Alarm set point 100 ppm
If you want to adjust the alarm set point you
need to calculate the voltage Output (+V) as
below:
The alarm voltage setting is 0,5 Volts.

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4.5 CALIBRATION
For proper use and to provide a correct signaling sensors must be tested.
The frequency and nature of testing or calibration may be determined by local regulation or
standards.
EN378 and the F-GAS Regulation require an annual check in accordance with the manufacturer’s
recommendation.
Suitably qualified operators of the unit should be aware of the regulations and standards set down
by the industry/country for the testing or calibration of this unit.
This manual is only intended as a guide and, insofar as permitted by law, the manufacturer
accepts no responsibility for the calibration, testing, or operation of this unit.
Check local regulations on calibration or testing requirements.
The GDS and GDI Gas Sensors contains sensitive electronic components that can be
easily damaged.
Do not touch nor disturb any of these components
NOTE: For improved accuracy and response, the instrument should be zeroed and calibrated in
the environment in which it is being installed.
IMPORTANT RECCOMENDATIONS:
Before testing the sensors on-site, the GDS or GDI must have been powered up and allowed
to stabilize.
The GDS or GDI is calibrated at the factory. After installation, a zero adjustment maybe
required due to differences in environmental conditions.
If the GDS or GDI is exposed to a large leak it should be tested to ensure correct functionality
by electrically resetting the zero setting and carrying out a bump test. See specific Dixell
manual for this procedure.
Dixell recommends annual checks and gas calibration. Dixell also recommends sensor
replacement every 3 years or as required.
Calibration frequency may be extended based on application, but should never exceed 2
years.
In applications where life safety is critical, calibration should be done quarterly (every 3
months) or on a more frequent basis.
Dixell is not responsible for setting safety practices and policies. Safe work procedures
including calibration policies are best determined by company policy, industry standards, and
local codes.
Failure to test or calibrate the unit in accordance with applicable instructions and with industry
guidelines may result in serious injury or death.
The manufacturer is not liable for any loss, injury, or damage arising from improper testing,
incorrect calibration, or inappropriate use of the unit.
The testing and/or calibration of the unit must be carried out by a suitably qualified technician, and
must be done:
in accordance with this manual
in compliance with locally applicable guidelines and regulations.
NOTE: The full procedure for the specific calibration and the technical equipment to use is
described on Dixell Calibration Manual.

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4.6 HOUSING DIMENSIONS
Dimensions for the GD Gas Sensors with IP41 housing:
Dimensions for the GD Gas Sensors with IP66 housing:

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5. TROUBLESHOOTING
SYMPTOM
POSSIBLE CAUSE(S)
Green and Red LED off
Check power supply.
Check wiring.
GDS or GDI was possibly damaged in transit.
Check by installing another GDS or GDI to confirm the fault.
Red LED on and Green
LED off (Fault)
Sensor may be disconnected from printed circuit board.
Check to see sensor is properly inserted into board.
The sensor has been damaged or has reached the end of life
and needs to be exchanged.
Contact producer for instructions and support.
Alarm in the absence of a
leak
Try setting an alarm delay.
Perform a bump test to ensure proper operation.
6. MODBUS COMMUNICATION
6.1 COMMUNICATION SETTINGS
There are 256 selections, and the addresses are numbered 0 to 255 inclusive. Addresses are
selected by rotating the hexadecimal dial switches SW1 and SW2.
Values 1 to 247 are valid / usable addresses providing a unique identity for each gas detector.
Addresses 248 to 255 and address 0 are reserved for implementing specific features.
Modbus data with a zero in the address field is received by all detectors (irrespective of the
address selected by the dial switches) to enable the master device to broadcast simultaneously to
all the detectors.
Switch SW1 selects addresses 0 to 15 and switch SW2 multiplies the address by a factor of 16.
Technical communication data are:
Baud rate: 9,600 or 19,200 (selectable)
Start bits: 1
Data bits: 8
Parity: none
Stop bits: 1
Retry time: 500 ms (min time between retries)
End of message: silent 3.5 characters

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6.2 WIRING AND ADDRESSING
ITEMS
DESCRIPTION
Wiring for Modbus
RS485
Modbus connector is CN4.
Pin 1 GND
Pin 2 + TX/RX non-inverting signals
Pin 3 - TX/RX inverting signals
The 3-pin connections are designed for a 2-conductor wire with
a common drain shield.
Modbus Address
Hexadecimal Address Switches.
Used to set a unique address for the sensor when multiple
sensors are connected to a controller.
Valid addresses are 0-247.
Modbus addressing can be selected by the combined settings
on the hexadecimal dial switches SW1 and SW2.
Addresses 0-15 are selectable with switch SW1 (the least
significant portion of the address). SW2 scales the addresses
by a factor of 16 (the most significant portion of the address).
NOTE: Address 0 is reserved to enable the master to broadcast
to all of the detector slave devices.
Addresses 248-255 (0x8F –0xFF) are reserved.
Addresses 254 (0xEF) and 255 (0xFF) are reserved for setting
the Modbus communications Baud rates.
Network Connection

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6.3 BAUD RATE
GDS and GDI sensors use 9600 as default Baud rate.
It’s possible to change the Baud rate value, to apply this change select the address and reset the
gas detector by temporarily shorting jumper J4 (or by cycling the power off and on).
After the Baud rate is set, the desired Modbus address (1-247) can be selected by changing the
switch settings with a power-cycle or reset operation afterward.
6.4 ANALOG INPUT REGISTERS
The Register Map specifies the details of storage locations (registers and flags) within the
detectors.
Analog input registers are READ ONLY using function code 04.
REGISTER
DESCRIPTION
RANGE
UNIT
1000
Concentration gas level (% of full scale).
0-100
%
1001
Concentration gas level in ppm.
0-65.535
ppm
1003
Full scale sensor level in ppm.
0-65.535
ppm
1004
Alarm set-point (% of Full Scale).
0-100
%
1005
Sensor timer.
0-65.535
hours
1006
Detector address.
1-247
n/a
1007
Software version.
100
n/a
Concentration Registers 1000 and 1001:
The real-time gas concentration is available in different formats. Register 1000 keeps
track of the percentage concentration. Register 1001 maintains the detected
concentration in parts per million.
Full Scale Sensor Level (in ppm) Register 1003:
The full-scale sensor level is the maximum detectable gas concentration for the detector.
This maximum rating is stored in register 1003, so for example, 1003 holds the value
1000 to represent 1000 parts per million (ppm).

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Here below the graph of alarm activation (sensor with range 0-1000 ppm):
Scale %
100%
20%
0
Gas
Concentration
Scale ppm
1000
200
0%
OFF
Alarm
ON
Alarm Setpoint Full Scale
Alarm Set Point (% of Full Scale) Register 1004:
The Alarm Set Point is the threshold at which the gas concentration has reached a level
to warrant the activation of:
• The red LED (alarm indication)
• The relay
• The buzzer
• The alarm flag (by setting a 1 in register 3000).
The Alarm Set Point can be controlled per Section 5.2. Alternatively, a software value
can be written into register 2000 to set the alarm level in ppm and override the hardware
potentiometer setting until the software value is reset back to zero, so although register
1004 is a read only register, its value can be modified by writing to register 2000.
The Alarm Set Point register 1004 is measured as a percentage of the full scale. For
example, 1.0 Volts measured between TP1 and TP3 corresponds to a 20% Alarm Set
Point given that the maximum voltage is 5.0 Volts.
The Alarm Set Point register 1004 will contain 20 to represent 20% and this corresponds
to 200 ppm for a detector with a full scale range of 1000 ppm.
If a delay period (up to 59 minutes) is set in registers 2001, the red LED and the Alarm
Flag will be immediately activated, but the relay and the buzzer will wait for the duration
of the delay period to expire before the relay switches on
and the buzzer is audible. The duration of the delay is measured from the instant when
the gas concentration reaches the alarm set point and the red LED and the alarm flag
are activated.
For details on the working process, please see the flow chart nr.1
Sensor Timer Register 1005:
The sensor timer register keeps a count of the number of hours the sensor is on. The
register is incremented every hour and after one year the register will exceed 8760 hours
and the Test Flag will be set to 1 to indicate that the detector requires testing. The Test
Flag Register is located at address 4001 and can be cleared to indicate that the sensor
and detector have passed the annual test.
For details on the working process, please see the flow chart nr.2

1592038710 Gas Leak Detector Modbus GB 01.12.2016 GDS41M-GDS66M-GDI41M-GDI66M 20/28
Detector Address 1006:
The detector address is the value of address set by the hexadecimal switches.
Software Version 1007:
The software version is the revision of firmware operating on the processor of the
detector.
6.5 ANALOG OUTPUT HOLDING REGISTERS
The Register Map specifies the details of storage locations (registers and flags) within the
detectors.
Analog output holding registers are READABLE using function code 03, and WRITABLE using
function code 06.
REGISTER
DESCRIPTION
RANGE
DETAILS
2000
Alarm setpoint (ppm)
0-65.535
Alarm set-point.
Threshold in parts per
million.
2001
Alarm delay
0-59
The Alarm Delay is the time
in minutes after the gas
concentration exceeds the
alarm level and the Alarm
Flag Register 3000 is set to
1.
2002
Buzzer delay
0-59
The Buzzer Delay is the
time in minutes the buzzer is
deactivated for during the
alarm phase when the gas
concentration exceeds the
alarm set point.
Alarm Set Point (in ppm) Register 2000
The Alarm Set Point register 2000 stores the software setting for the alarm set point in
parts per million (ppm).
Writing the value zero into this register will enable the hardware potentiometer P1 to
determine the Alarm Set Point. If a value greater than zero and less than the full scale
sensor limit in ppm is written into register 2000 then the hardware potentiometer setting
is ignored and the value written into register 2000 determines the alarm set point.
For example, writing the value 500 into the Alarm Set Point register 2000 effectively
overrides the hardware alarm set point on the potentiometer P1 and sets the alarm gas
concentration threshold to 500 parts per million and will be displayed as 50 in register
1004 to represent 50% for a detector with a full scale range of 1000 ppm.
For details on the working process, please see the flow chart nr.3
Alarm Delay Register 2001
The Alarm Delay Register 2001 stores the software alarm delay period up to 59 minutes
and the jumpers J5 and J6 set the hardware alarm delay period.
The alarm delay is the duration between the unit detecting a gas concentration above
the alarm set point and the activation of the relay and the buzzer. If there is a jumper on
J5 or J6 or both J5 and J6 have jumpers on connecting the pins, the software value is