GDS GASMAX User manual

GDS Corp.
2513 Hwy 646 Santa Fe, Texas 77510
409-927-2980 409-927-4180 (Fax) ww.gdscorp.com
Operation and Maintenance
Manual
GASMAX/TX
Battery-Powered Dual Channel Wireless Gas Monitor

GASMAX/TX Operation & Maintenance Manual, Revision 1.0
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CAUTION: FOR SAFETY REASONS THIS EQUIPMENT MUST BE OPERATED AND
SERVICED BY QUALIFIED PERSONNEL ONLY. READ AND UNDERSTAND INSTRUCTION
MANUAL COMPLETELY BEFORE OPERATING OR SERVICING.
ATTENTION: POUR DES RAISONS DE SÉCURITÉ, CET ÉQUIPEMENT DOIT ÊTRE UTILISÉ,
ENTRETENU ET RÉPARÉ UNIQUEMENT PAR UN PERSONNEL QUALIFIÉ. ÉTUDIER LE
MANUE D’INSTRUCTIONS EN ENTIER AVANT D’UTILISER, D’ENTRETENIR OU DE
RÉPARER L’ÉQUIPEMENT.
REVISION HISTORY
Revision 1.0 8/1/13 Initial Release (updated 11/22/13)
Copyright © 2013 GDS Corp. All Rights Reserved
P/N 1200-0863-02

GASMAX/TX Operation & Maintenance Manual, Revision 1.0
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CONTENTS
1 SAFETY INFORMATION _______________________________________________ 8
2 GENERAL INFORMATION ______________________________________________ 9
3 SPECIFICATIONS ____________________________________________________ 10
4 OPERATION _______________________________________________________ 11
5 WIRELESS SYSTEM BASICS ____________________________________________ 14
System Architecture _________________________________________________________ 14
Transmission Distance _______________________________________________________ 15
Monopole and collinear Omni-Directional antennas _______________________________ 1
YAGI Directional Antennas ___________________________________________________ 17
Coaxial Cables ______________________________________________________________ 17
Surge Protection & Grounding_________________________________________________ 18
6 HARDWARE OVERVIEW ______________________________________________ 19
INSTALLATION _____________________________________________________ 21
Locating the GASMAX/TX ____________________________________________________ 21
Mounting the GASMAX/TX ___________________________________________________ 21
Power and Signal Wiring _____________________________________________________ 22
Connecting a Remote Antenna ________________________________________________ 22
Connecting A GASMAX/TX Remote Sensor _______________________________________ 23
Sealing Antenna and cable Fittings _____________________________________________ 24
Use in Hazardous Areas ______________________________________________________ 24
8 INITIAL SETUP______________________________________________________ 25
power-on and User Interface __________________________________________________ 25
Setting Up the GASMAX/TX and C2/TX Wireless Site Manager _______________________ 2

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Initial Setup – Legacy Mode ___________________________________________________ 27
9 CALIBRATION ______________________________________________________ 28
Calibration Overview ________________________________________________________ 28
Calibration Procedure _______________________________________________________ 29
10 OPERATION AND MAINTENANCE ____________________________________ 31
Data Display Screen _________________________________________________________ 31
Trend and Dual Data Display ScreenS ___________________________________________ 32
Normal Operation __________________________________________________________ 32
Optimizing Battery Life ______________________________________________________ 33
Alarm setup _______________________________________________________________ 33
Sensor Replacement ________________________________________________________ 34
Sensor Replacement – Remote Sensors _________________________________________ 35
Normal Maintenance ________________________________________________________ 35
11 USER MENUS ____________________________________________________ 36
Channel Configuration Menu__________________________________________________ 37
Device Setup Menu _________________________________________________________ 41
12 TROUBLESHOOTING GUIDE _________________________________________ 45
Sensor Indicates Fault or Overrange ____________________________________________ 45
Sensor Will Not ZERO ________________________________________________________ 45
GASMAX/TX EXHIBITS UNUSUAL OR UNEXPECTED BEHAVIOR _______________________ 45
GASMAX/TX Display Blank ___________________________________________________ 45
GASMAX/TX and C2/TX Wireless Site Manager Displayed Values Don’t Match __________ 45
Wireless Site Manager DISPLAYs Comm Error For a Single GASMAX/TX _______________ 4
Wireless Site Manager DISPLAYs Comm Error For aLL GASMAX/TX ___________________ 4

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13 SPARE PARTS ____________________________________________________ 4
Display & Enclosure _________________________________________________________ 47
Sensor Head Accessories _____________________________________________________ 48
Sensor Separation Kit ________________________________________________________ 48
14 DRAWINGS AND DIMENSIONS ______________________________________ 49
15 NETWORK PARAMETERS ___________________________________________ 50

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TABLE OF FIGURES
FIGURE 4-1: GASMAX/TX BLOCK DIAGRAM ............................................................................................. 11
FIGURE 5-1: GDS CORP WIRELESS SYSTEM ARCHITECTURE ...................................................................... 14
FIGURE 5-2: RF TRANSMISSION MARGIN ................................................................................................. 15
FIGURE 5- : RF TRANSMISSION ZONE ..................................................................................................... 16
FIGURE 5-4: VERTICALLY POLARIZED OMNI-DIRECTIONAL AND YAGI ANTENNAS ..................................... 17
FIGURE 6-1: GASMAX/TX WITH SINGLE LOCAL SENSOR ........................................................................... 19
FIGURE 6-2: GASMAX/TX WITH DUAL SENSORS ....................................................................................... 20
FIGURE 6- : P/N 10-0411 REMOTE SENSOR SEPARATION KIT .................................................................. 20
FIGURE 7-1: GASMAX/TX I/O BATTERY BOARD ........................................................................................ 22
FIGURE 7- : CONNECTING A GASMAX/TX REMOTE SENSOR .................................................................... 2
FIGURE 8-1: GASMAX/TX DISPLAY ........................................................................................................... 25
FIGURE 8-2; STEP-BY-STEP SETUP CHECKLIST .......................................................................................... 26
FIGURE 9-1: CALIBRATION SETUP ............................................................................................................ 29
FIGURE 9-2: CALIBRATION FLOWCHART .................................................................................................. 0
FIGURE 10-1: GASMAX/TX DATA DISPLAY SCREEN ................................................................................... 1
FIGURE 10-2: DUAL DATA AND TREND DISPLAY SCREENS ........................................................................ 2
FIGURE 10- : GASMAX/TX SENSOR REPLACEMENT ................................................................................. 4
FIGURE 11-1: GASMAX/TX MAIN MENU TREE ......................................................................................... 6
FIGURE 11-2: CHANNEL CONFIGURATION MENU .................................................................................... 7
FIGURE 11- : ALARM SETTINGS MENU .................................................................................................... 8
FIGURE 11-4: SMART SENSOR INFORMATION MENU............................................................................... 9
FIGURE 11-5: TECHNICIANS MENU .......................................................................................................... 9
FIGURE 11-6: SET UNITY GAIN MENU ...................................................................................................... 40
FIGURE 11-7: PREAMP GAIN SET MENU .................................................................................................. 40
FIGURE 11-8: RF LINK TEST MENU ........................................................................................................... 41
FIGURE 11-9: RADIO SETUP MENU (2.4 GHZ)........................................................................................... 41
FIGURE 11-10: CLOCK / DELAY MENU...................................................................................................... 42
FIGURE 11-11: SECURITY MENU .............................................................................................................. 4
FIGURE 11-12: LCD CONTRAST MENU ..................................................................................................... 4
FIGURE 11-1 : POWER OFF MENU .......................................................................................................... 44
FIGURE 1 -1: GASMAX/TX + LOCAL SENSOR SPARE PARTS ...................................................................... 47
FIGURE 1 -2: GASMAX SENSOR HEAD SPLASH GUARD& FLOW CELL ........................................................ 48

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FIGURE 1 - : GASMAX/TX REMOTE SENSOR SEPARATION KIT ................................................................. 48
FIGURE 14-1: GASMAX/TX DIMENSIONS (SINGLE LOCAL SENSOR) ........................................................... 49
FIGURE 15-1: GDS CORP NETWORK IDENTIFIERS ..................................................................................... 50

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1SAFETY INFORMATION
Important – Read Before Installation
Users should have a detailed understanding of GASMAX/TX operating and maintenance instructions. Use
the GASMAX/TX only as specified in this manual or detection of gases and the resulting protection
provided may be impaired. Read the following WARNINGS prior to use.
WARNINGS
•The GASMAX/TX gas monitor described in this manual must be installed, operated and
maintained in accordance with information contained herein. Installation in any hazardous area
must comply with all applicable restrictions, requirements and guidelines for said hazardous
areas. It is the end user customer’s final decision to ensure that the GASMAX/TX is suitable for
the intended use.
•The GASMAX/TX is designed and constructed to measure the level of certain gases in ambient
air. Accuracy in atmospheres containing steam or inert gases cannot be guaranteed.
•Always mount the sensor head vertically with the sensor head facing down.
•Do not paint transmitter or sensor assembly.
•Do not operate the GASMAX/TX if its enclosure is damaged or cracked or has missing
components. Make sure the cover, internal PCB’s and field wiring are securely in place before
applying power.
•Do not expose the GASMAX/TX to electrical shock or continuous severe mechanical shock.
Protect the GASMAX/TX and related sensor assemblies from dripping liquids and high power
sprays.
•Calibrate with known target gas at start-up and check on a regular schedule, at least every 90
days. More frequent inspections are encouraged to spot problems such as dirt, oil, paint, grease
or other foreign materials on the sensor head.
•Periodically test for correct operation of the system’s alarm events by exposing the monitor to a
targeted gas concentration above the High Alarm set point.
•Use only for applications described within this manual.

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2GENERAL INFORMATION
The GDS Corp GASMAX/TX Wireless Gas Monitor and matching C2/TX Wireless Site Manager work
together seamlessly to deliver highly reliable, cost effective, customer-friendly solutions for
wireless gas detection. The GASMAX/TX can also be used in ‘legacy mode’ with existing GDS Corp
Wireless Controller / Receivers such as the C1 Protector, C64 Protector or C2 Quad Protector
Controller / Receiver.
The GASMAX/TX supports one or two local or remote sensors for toxic gases, carbon
dioxide or hydrocarbon combustibles. The advanced microcontroller, non-intrusive
magnetic interface and superior graphic LCD display offers rapid setup,
simplified operation and enhanced diagnostics not found in previous
generation products.
The GASMAX/TX’s tightly integrated radio modem utilizes frequency hopping
spread spectrum (FHSS) technology to provide reliable transmission of gas
concentration data and detector status across long distances while using very little power.
Battery life can be as long as one year under common circumstances. Instead of complicated
setup procedures that involve channel selection and identification codes, the GASMAX/TX is
configured using a single network identifier letter and single device number. When configured as part of
a system with a third-generation C2/TX Wireless Site Manager, all configuration and setup information
programmed into the GASMAX/TX is automatically transmitted to the C2/TX Wireless Site Manager,
eliminating redundant setup and minimizing programming errors.
Key features:
•Single or dual channel, toxic and/or combustible using new Ultra-Low-Power Infrared for
Combustibles and Carbon Dioxide
•Six to 12 month battery life on one replaceable .6VDC Lithium battery
•Tightly integrated 900MHz or 2.4 GHz radios with Frequency Hopping Spread Spectrum (FHSS) for
maximum range
•Automatic sensor recognition and setup with GDS Corp Smart Sensors
•Large LCD shows values, bar-graph and RF interface
•User-prompted calibration procedure
•Power on / Power off using magnetic wand – no need to open the enclosure
•Suitable for use in Class I Division 1 Hazardous Areas with XP rated antenna coupler

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3SPECIFICATIONS
Power Disposable .6v Lithium-Ion battery (D-size)
Display 64 x128 pixel LCD with engineering units, bargraph and 0-minute trend
Ch 1 Input Digital input from local or remote type 10-97xx toxic or infrared sensors
Ch 2 Input Digital input from local or remote type 10-97xx toxic or infrared sensors
Accuracy +/- 5% of full scale (typical) over temperate range
Output Gas concentration represented by a wirelessly transmitted numeric value between 800
counts (0% of scale) and 4000 counts (100% of scale); one data value per channel. Alarm
status bits and battery voltage information is also transmitted.
RF Section
(900 MHz)
User adjustable transmit power from 10 mW ( ) to 1.0 watt (+ 0 dBm); frequency range
from 902 to 928 MHZ. Beacon receiver sensitivity -100 dBm
RF Section
(2.4 GHz)
Fixed transmit power of 50 mW. Frequency range from 2.406 GHz to 2.4 5 GHz (network
identifier A – R) and from 2.444 GHz to 2.472 GHz (network identifier S – Z)
Temperature -40°C to +55°C
Memory On-board non-volatile memory retains all user settings
Housing Aluminum housing with epoxy paint standard; # 16 stainless steel optional
Dimensions Width 5.4” (1 7 mm), Height 8” (20 mm), Depth 5” (127 mm) Shipping wt. 6.5 lbs. ( kg)
Approvals Enclosure CSA certified for Class I Division 1 hazardous areas
Warranty Two years on electronics, one year on sensor
AVAILABLE SENSORS AND RANGES
P/N Sensor Range P/N Sensor Range
10-9750 Methane 0-100% LEL 10-975 Carbon Dioxide 0-100%
10-9751 Propane 0-100% LEL
10-9710 Oxygen 0-25% 10-9722 Ethylene Oxide 0-100 ppm
10-9711 Carbon Monoxide 0- 00 ppm 10-972 Arsine 0-1 ppm
10-9712 Chlorine 0-10 ppm 10-9724 Silane 0-50 ppm
10-971 Chlorine Dioxide 0-1 ppm 10-9725 Fluorine 0-1 ppm
10-9714 Hydrogen 0-4% 10-9726 Phosgene 0-1 ppm
10-9715 Hydrogen Sulfide 0-9999 ppm 10-9727 Hydrazine 0-1 ppm
10-9716 Hydrogen Cyanide 0- 0 ppm 10-9728 Nitric Oxide 0-50 ppm
10-9717 Hydrogen Chloride 0- 0 ppm 10-9729 Nitrogen Dioxide 0-100 ppm
10-9718 Hydrogen Fluoride 0-5 ppm 10-97 0 Mercaptan 0-50 mg/m
10-9719 Sulfur Dioxide 0-500 ppm 10-97 1 Tetrahydrothiophene 0-50 mg/m
10-9720 Ammonia 0-1000 ppm 10-97 2 Diborane 0-1 ppm
10-9721 Ozone 0-1 ppm 10-97 Hydrogen Sulfide Low RH 0-100 ppm

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4OPERATION
The GASMAX/TX wireless gas monitor is designed to detect dangerous levels of toxic or hydrocarbon
combustible gases and transmit that information to a GDS Corp remote site manager or controller /
receiver.
The GASMAX/TX uses the new highly integrated 10-97xx series ultra-low-power infrared or zero power
electrochemical Smart Sensors that allow each sensor to be individually optimized for the target gas,
range and environmental conditions.
Figure 4-1: GASMAX/TX Block Diagram
Toxic gases entering the sensor head react with the electrolyte in the sensor to produce a small electrical output
signal. Electronics on the sensor board amplify the signal (“PGA Gain”) and covert the information from
analog to digital using a 12-bit A/D converter. If an ultra-low-power infrared sensor is being used,
hydrocarbon gases enter the sensor and block the passage of infrared light from the IR source to the
detector. An integrated microprocessor in the infrared sensor linearizes the value and converts the output
to digital.
IMPORTANT: TOXIC SENSORS ARE SUBJECT TO ACCELERATED DETERIORATION IF POWER IS NOT APPLIED
WITHIN MONTHS OF SHIPMENT FROM GDS CORP.
12
ZZzzz
“PGA Gain”
Adjustment
Sensor
Element
Sensor Digital Output:
800 counts = 0%
4000 counts = 100%
High
Resolution
LCD Display
Sensor
Amplifier
A/D
User Interface & System Control
Process
Alarms
Scale & Convert to
Engineering Units
Apply Calibration
Gain & Offset
.6V Battery
900 MHz or
2.4 GHz Radio
Central
Processor
Toxic or Combustible
Gas
Data
Transmission
to WSM

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IMPORTANT: THE GASMAX/TX INFRARED SENSOR WILL NOT DETECT COMBUSTIBLE LEVELS OF
HYDROGEN GAS.
Every six seconds, the GASMAX/TX central processor wakes up, reads the sensor’s digital output, scales
and converts the reading to engineering units, applies correction factors based on the most recent
calibration and displays the value on the LCD display. Based on the gas concentration level and alarm
levels programmed by the user, the microprocessor then determines if a compact wireless data packet
should be broadcast to the site manager or wireless controller / receiver. This data packet includes the
gas value, alarm and fault status bits and battery voltage.
At the conclusion of each “Wakeup Timer” interval, the GASMAX/TX also transmits a larger data packet
containing additional information that includes zero and span values, user-programmed tag and
engineering unit values and communications timeout settings. Third-generation controllers such as the
C2/TX Wireless Site Manager process and display this information, eliminating the need to program both
the gas monitor and site manager or controller.
NOTE: GDS CORP WIRELESS GAS DETECTORS CAN ONLY COMMUNICATE WITH PROPERLY EQUIPPED GDS
CORP CONTROLLERS OR WIRELESS SYSTEM / SITE MANAGERS.
If the GASMAX/TX determines that a data packet should be transmitted, the following events take place:
Power is applied to the radio, the radio is placed in receive mode and listens for the synchronization
beacon transmitted by the site manager or controller / receiver. If the beacon is found, the radio
synchronizes to the beacon hopping pattern, transmits the data packet and returns to sleep mode. This
sequence takes between 250 milliseconds and 1 second to complete. If the radio fails to synchronize with
the beacon, it waits 2 seconds and tries again, then waits 2 seconds and tries once more. If the third
attempt fails an “Out of Range” icon is displayed and the GASMAX/TX goes to sleep until the next six
second interval occurs. The “Out of Range” event will be logged in the Event Log.
FHSS radios for both 900 MHz and 2.4 GHz are available. For North America, 900 MHz is recommended
due to increased power output available (up to 1 watt), greater range and ability of lower frequency
signals to travel around interfering objects. Systems utilizing 2.4 GHz radios transmit at lower power levels
and have corresponding less range. In addition, higher frequency 2.4 GHz signals tend to require a more
direct ‘line of sight’ between the gas detector and controller / receiver antenna. On the other hand, 2.4
GHz systems are generally license-free world-wide and are generally less prone to interference from other
radio frequency sources.

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NOTE: CHOICE OF FREQUENCY IS MADE AT TIME OF ORDER. SYSTEMS DESIGNED FOR 900 MHZ CANNOT
BE FIELD UPGRADED TO 2.4 GHZ AND VICE-VERSA.
Once the choice of frequency band is made, every device in the network must have a matching Network
Identifier (“A” - “Z”) that determines the radio’s frequency hopping pattern and system identifier. In
addition, each GASMAX/TX must also have a unique device ID (1 - 240) that allows the controller to
identify the specific gas detector. Finally, there must be one device that transmits the synchronizing
Beacon signal that all radios use to synchronize their transmissions.
While the GASMAX/TX is optimized for use with third-generation controllers such as the C2/TX Wireless
Site Manager, the GASMAX/TX can also be integrated into existing wireless networks that utilize a C1
Protector 16-channel controller, C64 Protector 64-channel controller or C2 Quad Protector 4-channel
controller. In “legacy mode”, the required ‘Hop Channel’, ‘System ID’ and ‘RTU Address’ values can be
programmed to match an existing network, and many of the benefits, including magnetic Power On /
Power Off, advanced 10-97xx sensor technology and additional transmission modes will still offer benefit
to the user. However, when in legacy mode, packet data that includes sensor range, tag name and
engineering units is not transmitted to the controller and must be manually entered in both the
receiver/controller and gas detector.

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5WIRELESS SYSTEM BASICS
SYSTEM ARCHITECTURE
GDS Corp wireless uses discrete Frequency-Hopping Spread-Spectrum radios to communicate gas and
alarm level information wirelessly between gas detectors and controllers. FHSS radios transmit individual
data packets using different discrete frequencies in a pseudorandom sequence (“Hop Pattern”) known to
both transmitter and receiver. Unlike Direct-Sequence Spread Spectrum (DSSS) used for short distance
802.11 b/g “WiFi” and certain mesh networks, FHSS technology provides an ideal balance between power
consumption, transmission distance and resistance to interference.
Figure 5-1: GDS Corp Wireless System Architecture
In each GDS Corp system, one device is configured as the “beacon server”. This device transmits a
modulated carrier signal that all other radios use to synchronize their frequency-hopping pattern.
Knowledge of the selected hopping pattern programmed into the radio and synchronization data from the
beacon enables each radio to know when to transmit, and on what frequency. Multiple networks can
exist in the same frequency band so long as their choice of pseudorandom hopping pattern is unique.
GASMAX/TX monitors support 26 unique network identifiers.
Beacon Signal (Constant)
Gas Data Packet
(As necessary)
Gas Data Packet
(As necessary)

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TRANSMISSION DISTANCE
In order for reliable wireless communication to occur, transmitter power output, antenna ‘gain’ and
receiver sensitivity must exceed the ‘free space loss’ attenuation experienced by radio signals as they
travel between transmitter and receiver. This gain or loss is measured in decibel-milliwatts (dBm) and is a
function of both distance and frequency. Typical free space loss at 900 MHz is -71 dBm at 00 ft / 100
meters and -91 dBm at 000 ft / 00 meters, and for 2.4 GHz the free space loss is -80 dBm at 00 ft/ 100
meters and -100 dBm at 000 ft / 1000 meters.
Figure 5-2: RF Transmission Margin
In a typical 2.4 GHz system shown above, for example, the transmitter power output is +21 dBm, each
antenna provides an additional gain of + dBm and the receiver sensitivity is -95 dBm. Therefore, the total
system gain is 21+ + -(-95) = 122 dBm. Since a reliable system requires a margin of +20 dBm, this system
will work if the free space loss between the transmitter and receiver is less than 102 dBm, suggesting a
distance of approximately 1000 meters. However, this calculation does not take into account additional
loses due to intervening structures or foliage.
To minimize free-space loss, the combined height of the transmitter antenna and receiver antenna should
exceed the diameter of the “RF Transmission Zone” (see Fig. 5- ) and at least 60% of the area inside the
zone should be free of obstacles. Although both 900 MHz and 2.4 GHz signals can travel around or
through most towers or buildings, structures such as large metal tanks or solid metal buildings may
attenuate the signal to the point where reception is marginal.
Raising the antenna at either end of the path will improve signal strength and reduce transmission errors.
GDS Corp recommends placing the GASMAX/TX at least 5 feet above the surrounding terrain, and even
more if possible. However, note that the standard antenna transmits its maximum signal strength in a
relatively flat ‘donut-shaped’ pattern which may affect the performance of GASMAX/TX monitors located
in close proximity to an elevated C2/TX Site Manager or receiver/controller.
RF Power
+21 dBm
Antenna
Gain = + dBm
Antenna
Gain = + dBm
2.4 GHz,
1000m
Free Space
Loss =
-102 dBm
Receiver
Sensitivity
-95 dBm

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Figure 5-3: RF Transmission Zone
GDS Corp always recommends that a wireless survey be completed at the site to ensure the integrity of
the wireless communications link. Special care should be taken to account for moveable obstacles such as
cranes, railroad cars, trucks, containers, and any other large ‘structures’ that could end up being placed –
temporarily – in a location that blocks the wireless signal.
MONOPOLE AND COLLINEAR OMNI-DIRECTIONAL ANTENNAS
Monopole “rubber duck” antennas are the most commonly used antennas for portable and semi-portable
equipment where extreme range or directional reception is required. When mounted vertically, they
provide good ‘omnidirectional’ reception and transmission from all horizontal directions, and are
generally rugged and when sealed properly against moisture can provide years of quality service.
Collinear antennas are more sophisticated and combine several vertical antennas that operate in parallel
to increase signal gain by focusing the reception pattern in a more horizontal plane.
Rubber duck and collinear antennas provide best performance when installed with at least 1 to 2
“wavelengths” away from walls or steelwork. Since wavelength proportional to frequency, 900 MHz
signals have a wavelength to approximately 12 inches and 2.4 GHz signals have a wavelength of about
inches. Therefore, 900 MHZ antennas should be installed with at least 2 feet of clearance and 2.4GHz
antennas at least inches of clearance from walls or structures. Antennas may be mounted with less
clearance but output will be reduced; this may not matter if the distances involved are short. It is
important the antenna mounting bracket to well connected to “earth” or “ground” for good lightning
surge protection.
Rubber duck or collinear antennas emit RF energy in ‘vertical polarization’, where the electric fields
oscillate in the vertical plane and the magnetic fields oscillate in the horizontal plane. Transmitting and
receiving antennas should always be oriented such that the polarization is the same.
Combined Antenna Height
Distance 900 MHz 2.4 GHz
100 Ft 10’ / m 6’ / 2m
500 Ft 22’ / 7m 15’ / 5m
1000 Ft 0’/ 10m 20’ / 6m
000 Ft 54’ / 17m N/A
RF Transmission Zone

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YAGI DIRECTIONAL ANTENNAS
Yagi antennas are directional along the central beam of the antenna. The folded element is towards the
back and the antenna should be “pointed” in the direction of the transmission. Yagi antennas should also
be mounted with at least 1 to 2 wavelengths of clearance from other objects. The polarity of the antenna
is the same as the direction of the orthogonal elements. For example, if the elements are vertical the Yagi
transmits with vertical polarity.
In networks spread over wide areas, it is common for a central receiver / controller to have an omni-
directional antenna (such as a collinear) and the remote GAMAX/TX monitors to have Yagi directional
antennas. In this case, as the omni-directional antenna will be mounted with vertical polarity, then the
Yagi’s must also have vertical polarity (see Fig. 5- ). Care needs to be taken to ensure the Yagi is aligned
correctly to achieve optimum performance.
Two Yagi antennas can be used for a point-to-to link. In this case they can be mounted with the elements
horizontally to give horizontal polarity. There is a large degree of RF isolation between horizontal and
vertical polarity (~ 0dB) so this installation method is recommended if there is a large amount of
interference from another system close by transmitting in vertical polarity.
Figure 5-4: Vertically Polarized Omni-Directional and YAGI Antennas
COAXIAL CABLES
When installing a coaxial cable between the GASMAX/TX and a remote antenna, constructing a loop of
cable below the antenna is always recommended. The loop allows water to drip off the bottom of the U
Always mount YAGI antennas with the
primary elements oriented in the same
direction as any omnidirectional
antennas in the same system

GASMAX/TX Operation & Maintenance Manual, Revision 1.0
Page 18
instead of into the connection, reduces installation strain and provides spare cable length in case later the
original connectors need to be replaced.
Avoid installing coax cables together in long parallel paths. Leakage from one cable to another has a
similar effect as mounting an antenna near another antenna.
SURGE PROTECTION & GROUNDING
Voltage surges primarily enter the GASMAX/TX via the antenna connection as a result of electrical
discharge in the atmosphere. Electrical energy follows the most direct path to earth and the best
protection is achieved by “draining” the surge energy to earth via an effective earth ground. Wireless
devices should have a solid connection to earth via a ground stake or ground grid if the soil has poor
conductivity. Solid connection means a large capacity conductor (not a small wire) with no coils or sharp
bends. All other devices connected to the GASMAX/TX, such as remote sensors, should be grounded to
the same ground point is possible. There can be significant resistance between different ground points
leading to very large voltage differences during lightning activity. As many wireless units are damaged by
earth potential surges due to incorrect grounding as direct surge voltage.
It is very difficult to protect against direct lightning strikes but the probability of a direct strike at any one
location is very small. Unfortunately, power line surges and electromagnetic energy in the air can induce
high voltage surges from lightning activity several miles away.

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HARDWARE OVERVIEW
The GASMAX/TX is a self-contained, battery-operated single or dual channel gas detector with local or
remote sensors. The unit consists of an explosion proof enclosure, sensor head (if utilizing a local sensor),
antenna tuned for either 900 MHz or 2.4 GHz frequency bands, a display module with microprocessor and
radio and I/O battery board that doubles as mounting hardware for the display. The display attaches to
the I/O battery board via a short multi-pin cable and two captive thumbscrews.
Figure 6-1: GASMAX/TX with Single Local Sensor
The GASMAX/TX wireless gas monitor is capable of monitoring two separate sensors. In certain cases, it is
appropriate to co-locate both sensors in a ‘local sensor’ configuration. When doing so, the GASMAX/TX is
configured with a Y-adapter that supports two independent electrochemical or infrared sensors (See Fig.
5-2).
Local Sensor Head
GASMAX/TX Display Module
900 MHz or 2.5 GHz Antenna
.6V Lithium Battery
Multi
-
pin cable
I/O Battery Board
XP
Enclosure
Radio Module
on backside

GASMAX/TX Operation & Maintenance Manual, Revision 1.0
Page 20
Figure 6-2: GASMAX/TX with Dual Sensors
The GASMAX/TX also supports remote sensors located up to 15 feet from the GASMAX/TX display. Figure
6- shows the Sensor Separation Kit required for each remote sensor.
Figure 6-3: P/N 10-0411 Remote Sensor Separation Kit
Dual Local Sensors with “Y” Adapter
GASMAX/TX with Local and Remote Sensor
Four-wire Sensor
Data Cable up to
15 ft. / m in
length
15’ / m
Sensor Data
Cable