Riken Keiki GX-2001 User manual

Model GX-2001
Operator’s Manual
Part Number: 71-0053RK
Revision: I
Released: 2/4/08
www.rkiinstruments.com

2 • Warranty Model GX-2001 Operator’s Manual
Warranty RKI Instruments, Inc., warrants the Model GX-2001 sold by us to be free
from defects in materials, workmanship, and performance for a period of
two years from the date of shipment from RKI Instruments, Inc. This
includes the instrument and the original sensors. Replacement parts are
warranted for 1 year from the date of their shipment from RKI Instruments,
Inc. Any parts found defective within their warranty period will be repaired
or replaced, at our option, free of charge. This warranty does not apply to
those items which by their nature are subject to deterioration or
consumption in normal service, and which must be cleaned, repaired, or
replaced on a routine basis. Examples of such items are:
Warranty is voided by abuse including mechanical damage, alteration,
rough handling, or repair procedures not in accordance with the instruction
manual. This warranty indicates the full extent of our liability, and we are
not responsible for removal or replacement costs, local repair costs,
transportation costs, or contingent expenses incurred without our prior
approval.
THIS WARRANTY IS EXPRESSLY IN LIEU OF ANY AND ALL OTHER WARRANTIES
AND REPRESENTATIONS, EXPRESSED OR IMPLIED, AND ALL OTHER OBLIGATIONS
OR LIABILITIES ON THE PART OF RKI INSTRUMENTS, INC., INCLUDING BUT NOT
LIMITED TO THE WARRANTY OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE. INNO EVENT SHALL RKI INSTRUMENTS, INC., BE LIABLE
FOR INDIRECT, INCIDENTAL, OR CONSEQUENTIAL LOSS OR DAMAGE OF ANY KIND
CONNECTED WITH THE USE OF ITS PRODUCTS OR FAILURE OF ITS PRODUCTS TO
FUNCTION OR OPERATE PROPERLY.
This warranty covers instruments and parts sold to users only by
authorized distributors, dealers, and representatives as appointed by RKI
Instruments, Inc.
We do not assume indemnification for any accident or damage caused by
the operation of this gas monitor and our warranty is limited to replacement
of parts or our complete goods.
Absorbent cartridges
Filter elements, disks, or sheets
Pump diaphragms and valves

Model GX-2001 Operator’s Manual Table of Contents • 3
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Sensor Retainer/Sensor Cover Retainer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Sensors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Scrubber Filters/Sensor cover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
LCD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Control Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Printed Circuit Boards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Alarm Lights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Buzzer/Vibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Battery Pack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Belt Clip. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Battery Charger. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Start Up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Start-up Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Performing a Demand Zero. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Turning Off the Model GX-2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Normal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Displaying Peak Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Displaying STEL and TWA Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Combustible Gas Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Alarms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Aspirator Adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Displaying and Setting the Alarm Points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Setting the Time and Date. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4 • Table of Contents Model GX-2001 Operator’s Manual
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Setting the Zero Readings for All Target Gasses . . . . . . . . . . . . . . . . . . . . . . . . 28
Single Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Auto Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Recharging the Battery Pack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Replacing the Battery Pack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Replacing the Scrubber Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Replacing the Sensor Cover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Replacing a Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Rotating the Belt Clip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Parts List. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
WARNING: Understand manual before operating. Substitution of
components may impair intrinsic safety. To prevent
ignition of a hazardous atmosphere, batteries must only
be changed or charged in an area known to be
nonhazardous. Not tested in oxygen enriched
atmospheres (above 21%).

Model GX-2001 Operator’s Manual Introduction • 5
Introduction
Using an advanced detection system consisting of four gas sensors, the
Model GX-2001 Personal Four-Gas Monitor detects the presence of
combustible gas, oxygen (O2), carbon monoxide (CO), and hydrogen
sulfide (H2S) simultaneously. The Model GX-2001’s compact size and
easy-to-use design makes it ideally suited for a wide range of applications,
including sewage treatment plants, utility manholes, tunnels, hazardous
waste sites, power stations, petrochemical refineries, mines, paper mills,
drilling rigs, and fire fighting stations. The Model GX-2001 offers a full
range of features, including:
• Simultaneous four-gas monitoring of combustible gases, O2, CO, and
H2S
• Liquid crystal display (LCD) for complete and understandable
information at a glance
• Distinctive audible/vibrating alarms for dangerous gas conditions and
audible alarms for unit malfunction
• Glow in the dark control buttons.
• Microprocessor control for reliability, ease of use, and advanced
capabilities
• Alarm trend data
• Data logging functions
• STEL/TWA and over range alarm display
• Peak hold and average readouts
• Built-in time function
• RF shielded and high impact plastic case of very compact size and light
weight
• Belt clip for “hands-free” gas monitoring
• CSA classified for Class I, Division I, Groups A, B, C, and D hazardous
atmospheres
WARNING: The Model GX-2001 detects oxygen deficiency and
elevated levels of oxygen, combustible gases, carbon
monoxide, and hydrogen sulfide, all of which can be
dangerous or life threatening. When using the Model GX-
2001, you must follow the instructions and warnings in
this manual to assure proper and safe operation of the
unit and to minimize the risk of personal injury.

6 • Specifications Model GX-2001 Operator’s Manual
Specifications
Table 1: Model GX-2001 Specifications
Model Name Model GX-2001
Target Gas Combustibles
(Methane
calibration
standard)
Oxygen (O2) Hydrogen
Sulfide
(H2S)
Carbon
Monoxide
(CO)
Range
(Increment) 0-100% LEL (1% LEL) 0-40.0 vol% (0.1 vol%) 0-100 ppm (0.5 ppm) 0-500 ppm (1 ppm)
Detection
Method Diffusion
Response
Time T90 Within 30 Seconds
Display 7-Segment Digital LCD
Gas Alarms
(Factory
Settings)
Alarm 1: 10%
LEL
Alarm 2: 50%
LEL
Over: 100%
LEL
Alarm 1: 19.5
vol%
(Decreasing)
Alarm 2: 23.5
vol%
Over: 40.0
vol%
Alarm 1: 10
ppm
Alarm 2: 30
ppm
TWA: 10 ppm
STEL: 15 ppm
Alarm 1: 25
ppm
Alarm 2: 50
ppm
TWA: 25 ppm
STEL: 200
ppm
Operating
Temperature
and Humidity
-10 to 40oC/Below 85% RH (Without Condensation)
Safety/
Regulatory C US
186718
CSA classified, “C/US”, asIntrinsically Safe. Exia. Class I, Groups A,
B, C, &D. Class I, Zone 0, Group IIC. Temperature Code T3C.
Power Supply Ni-cad or Ni-MH Battery Pack (2.4 VDC Nominal), Direct Charging
Continuous
Operating
Hours
Up to 10 Hours (Non Alarm Operation After Full Charge), Ni-Cad
Up to 18 Hours (Non Alarm Operation After Full Charge), Ni-MH
Case High-impact Plastic, RF Shielded, Dust and Weather Proof
Required
Accessories Charger Station or Charger/Downloading Station w/Software & Cable

Model GX-2001 Operator’s Manual Specifications • 7
Other
Accessories • Charging Station with PC Communication Function for Datalog
Downloading
• Communication Computer Cable
• Communication Software (Windows®95, 98, NT)
• Automatic Calibration Station
• Hand Aspirated Sample Draw with Hose and Probe
• Wrist Strap (included with every unit)
• Neck Strap
Dimensions
and Weight Dimensions: 2.8 (H), 2.2 (W), 1.1 (D) inches Weight: Approximately 6 oz.
Table 1: Model GX-2001 Specifications
Model Name Model GX-2001

8 • Description Model GX-2001 Operator’s Manual
Description
This section describes the components of the Model GX-2001. These
components include the Model GX-2001’s case, sensors, LCD, control
buttons, printed circuit boards, alarm lights, buzzer/vibrator, battery pack,
belt clip, and battery charger.
Case
The Model GX-2001’s sturdy, high-impact plastic and metal case is radio
frequency (RF) resistant, and is suitable for use in many environmental
conditions, indoors and out. The unit is dust proof and weather resistant.
On the front of the case is a digital LCD, which shows gas concentrations,
battery level, time, and other readings including TWA, STEL, and peak gas
levels. Below the LCD are three glow in the dark control buttons. The first
button on the left is labeled MODE/POWER. The other buttons are labeled
DISP and AIR, respectively.
Sensor Cover Retainer
Sensor Retainer
MODE DISP AIR
HC
02
RKI
GX-2001
LCD
H2S
CO
Belt
Clip
Battery Charging
Contacts
IR Port
Control Buttons
POWER
Sensor Diffusion
Port, 4X
Alarm Lights
Figure 1: Components of the Model GX-2001

Model GX-2001 Operator’s Manual Description • 9
Beneath the control buttons is the buzzer/vibrator, which is located inside
the unit.
On the right side of the Model GX-2001 are the diffusion ports for the gas
sensors located inside the case. These sensors are, from top to bottom
(and are marked on the case), O2, HC (combustible gases), CO, and H2S.
On the left side of the case are two brass recharging contacts, which are
used when the unit is placed in the battery charger, and on top of the case
are two alarm lights. There is also an IR (infrared) communications port on
the left side which is used when downloading data to a computer using the
datalogging station. On the back of the unit is a rugged metal belt clip
enabling hands-free gas monitoring.The belt clip may be oriented as shown
in Figure 1 or rotated 180° depending on how the instrument is used.
Sensor Retainer/Sensor Cover Retainer
The sensorretainer holds the gas sensors in place and snaps onto the right
side of the case. It has 4 diffusion ports, one for each sensor, and has
recessed areas in it for the charcoal filter, the H2S removal filters, and the
sensor cover. The sensor cover retainer snaps onto the sensor retainer.
Two screws secure the sensor retainer and the sensor cover retainer to the
case.
Sensors
The Model GX-2001 uses four sensors to monitor HC (combustible gases),
O2, CO, and H2S simultaneously. The sensors are protected by filters that
allow atmosphere to diffuse inward. The sensors use different detection
principles, as described below.
Combustible Gas Sensor
The LEL sensor detects combustible gas and vapors in the atmosphere
with a catalytic element. The reaction of gas with oxygen on the catalyst
causes a change in the resistance of the element which affects the current
flowing through it. The current is amplified by the Model GX-2001’s
circuitry, converted to a measurement of combustible gas concentration,
and displayed on the LCD.
CAUTION: Do not expose the combustible sensor to high concentrations
of combustible gas such as that from a butane lighter.
Exposure to high concentrations of combustible gas may
adversely affect the performance of the sensor.

10 • Description Model GX-2001 Operator’s Manual
Oxygen Sensor
The O2sensor is a galvanic type of sensor. A membrane covers the cell
and allows gas to diffuse into the cell at a rate proportional to the partial
pressure of oxygen. The oxygen reacts in the cell and produces a voltage
proportional to the concentration of oxygen. The voltage is measured by
the Model GX-2001’s circuitry, converted to a measurement of gas
concentration, and displayed on the LCD.
CO and H2S Sensors
The CO and H2S sensors are electrochemical cells that consist of two
precious metal electrodes in an acid electrolyte. A gas permeable
membrane covers the sensor face and allows gas to diffuse into the
electrolyte. The gas reacts in the sensor and produces a current
proportional to the concentration of the target gas. The current is amplified
by the Model GX-2001’s circuitry, converted to a measurement of gas
concentration, and displayed on the LCD.
Scrubber Filters/Sensor Cover
Charcoal Filter Disk
The charcoal filter disk is located in the CO senor diffusion port of the
sensor retainer. It is black, has a woven texture, and is impregnated with an
H2S absorbing material. It fits into a recessed area of that port. The CO
sensor will respond if exposed to H2S and certain hydrocarbon gasses.
The charcoal filter scrubs these gasses out of the gas sampled to avoid
false CO readings. The H2S absorbing material added to the charcoal filter
extends it’s H2S absorbing life. If false or elevated CO readings are
noticed, especially in the presence of H2S, change the charcoal filter disk.
NOTE: Two H2S removal filter disks are used over the charcoal filter as
an additional guard against false CO readings as described below.
H2S Removal Filter Disks
The H2S removal filter disks are used in two locations. Two H2S removal
filter disks are located in a recessed area of the combustible gas sensor
diffusion port in the sensor retainer. Two are also used over the charcoal
filter disk in the CO diffusion port to extend the life of the charcoal filter. The
H2S removal filter disks are white when new. They scrub H2S out of thegas
sampled to increase the life of the combustible sensor and the charcoal
filter disk. They darken as they absorb H2S and must be changed when
they turn to a dark brown color. The recommended replacement frequency
will depend on how often the unit is exposed to H2S and the concentration.
Check the condition of the H2S removal filter disks quarterly.

Model GX-2001 Operator’s Manual Description • 11
Sensor Cover
The sensor cover is white and protects the scrubber filters and sensors
from dust and water. It fits over all the sensor diffusion ports and is secured
in place by the sensor cover retainer. If the sensor cover becomes dirty, the
accuracy of the GX-2001 will be affected. Replace the sensor cover if it
appears dirty.
LCD
The LCD is visible through the GX-2001’s front panel. Target gas
concentrations, the time, battery condition, and alarm indications are
displayed on the LCD. When any of the control buttons are pressed, the
LCD backlight comes on for 20 seconds.
Control Buttons
Below the LCD are the glow in the dark control buttons. These buttons are
MODE/POWER, DISP, and AIR. They turn on the power to the Model GX-
2001, and turn it off. They control what is displayed on the LCD, including
battery level, time, date, and year, gas concentrations, peak, TWA, and
STEL readings, as well as other messages. They also allow you to perform
a Demand Zero, change alarm points, change the date and time, and
calibrate the instrument. The functions performed by the control buttons
are summarized in the following table:
Table 2: The Control Buttons of the Model GX-2001
Button Function
MODE/POWER
• Turns the unit on and off.
• Turns the LCD back light on.
• Displays peak readings (low minimum and high
maximum readings for O2).
• Resets the alarm circuit (gas alarms).
• Enters Calibration Mode with the AIR button.
• Enters Alarm Adjustment Mode with the AIR
button.
• Enters Time Adjustment Mode with the DISP
button.

12 • Description Model GX-2001 Operator’s Manual
Printed Circuit Boards
The primary function of the Model GX-2001’s three printed circuit boards
are to amplify the current sent to them from the four gas sensors, convert
the current to a meaningful measurement of gas concentration, display the
gas concentration on the LCD, store peak, STEL, and TWA readings, and
activate the alarm circuit if an alarm point has been reached. They monitor
battery level, battery failure, and sensor failure. They also control the
Model GX-2001’s time function and the various operating modes of the
unit.
NOTE: The printed circuit boards contain no user serviceable parts.
Alarm Lights
The Model GX-2001 has two alarm lights located on top of the unit. The
alarm lights are two red LEDs that alert you to gas, low battery, and sensor
failure alarms.
DISP
• Turns the LCD back light on.
• Displays the next target gas when the unit is in
Measuring Mode.
• Enters Time Adjustment Mode with the MODE/
POWER button.
• Decreases settings when the unit is in Alarm
Adjustment Mode or Time Adjustment Mode.
• Toggles between field calibration and auto
calibration when the unit is in Calibration Mode.
AIR
• Turns the LCD back light on.
• Adjusts LCD readings when the a Demand Zero is
performed.
• Enters Calibration Mode with the MODE/POWER
button.
• Enters Alarm Adjustment Mode with the MODE/
POWER button.
• Increases settings when the unit is in Alarm
Adjustment Mode or Time Adjustment Mode.
• Toggles between field calibration and auto
calibration when the unit is in Calibration Mode.
Table 2: The Control Buttons of the Model GX-2001
Button Function

Model GX-2001 Operator’s Manual Description • 13
Buzzer/Vibrator
A solid-state electronic buzzer/vibrator is mounted inside the front case of
the Model GX-2001. The buzzer/vibrator sounds and vibrates for gas
alarms, and it sounds for unit malfunctions, low battery voltage, and as an
indicator during normal use of the many display options of the Model GX-
2001.
Battery Pack
Inside the Model GX-2001 is either a Ni-cad or Ni-MH battery pack that
supplies 2.4 V to the unit. The battery will run the unit for approximately 10
hours (Ni-Cad) or 18 hours (Ni-MH) when no alarms have been activated
during that time period. The battery is fully rechargeable when the Model
GX-2001 is placed into the battery charger. The battery icon on the LCD
shows the charge remaining in the battery. When the Model GX-2001
detects a low battery voltage, a low battery warning is activated. The
battery can be replaced by removing the belt clip on the back of the Model
GX-2001. See the maintenance section of this manual for instructions
about recharging and replacing the battery.
Belt Clip
On the back of the Model GX-2001 is a belt clip. The belt clip permits the
unit to be worn on a belt or to be clipped to a pocket for hands-free gas
monitoring. The belt clip may oriented as shown in Figure 1 or rotated 180°.
See the Maintenance section for instructions on how to rotate the clip.
Battery Charger
The Model GX-2001 has three battery charger accessories available. All
three are used to recharge the unit’s battery pack and serve as a
convenient station for auto calibration. The battery charger with the PC
communication feature has a datalogging port for the down loading of data
from the Model GX-2001 to a computer and allows autocalibration using a
computer. See “Parts List” for more information.

14 • Start Up Model GX-2001 Operator’s Manual
Start Up This section explains how to start up the Model GX-2001 and to get it ready
for operation.
Start-up Procedure
1. Press and hold the MODE/POWER button for one second to turn on the
Model GX-2001 and to activate its LCD. The alarm lights flash, the
buzzer sounds, and the vibrator vibrates.
2. The Model GX-2001 tests all elements of the LCD, then displays the
year, month, day, and time before displaying the battery voltage. The
buzzer sounds again after the battery voltage is displayed.
CAUTION: If the battery level is low or if the battery icon is flashing and
the unit’s buzzer sounds, recharge the Model GX-2001’s
battery.
3. The four gas sensors inside the Model GX-2001 begin working, and the
concentrations of the target gases are displayed on the LCD in the
following order: O2, H2S, CO, and HC. The Model GX-2001 is now in
Measuring Mode. Oxygen is displayed as a percentage (%), H2S and
CO as parts per million (ppm), and HC (combustible gases) as a
percentage of the lower explosive limit (% LEL).
NOTE: You can test the oxygen sensor and alarm circuit by exhaling into
the oxygen sensor. When the LCD reading falls below the alarm
point for oxygen, the buzzer will sound, the vibrator will activate,
the LCD reading for oxygen will flash, and the alarm lights will turn
on.

Model GX-2001 Operator’s Manual Start Up • 15
Performing a Demand Zero
Before using the Model GX-2001, it is a recommended to set the zero
reading (demand zero) for the target gasses to ensure accurate gas
readings in the monitoring environment.
1. Find a fresh-air environment. This is an environment free of toxic or
combustible gasses and of normal oxygen content (20.9%).
2. With the unit on and in Measuring Mode, press and hold the AIR button
for about three seconds to allow the Model GX-2001 to set the zero
reading for HC, CO, and H2S and to set the span for O2.
While you are pressing the AIR button, the LCD displays “Hold,” a
prompt for you to keep pressing the AIR button.
3. When the zero readings have been set, the LCD displays “Adj,” which
prompts you to release the AIR button.
Turning Off the Model GX-2001
1. Press and hold the MODE/POWER button for about five seconds to
turn off the unit.
2. The buzzer will sound and the LCD back light will flash.
3. Release the button when the LCD is blank. The unit is off.

16 • Operation Model GX-2001 Operator’s Manual
Operation
This section describes the normal operation of the Model GX-2001. It
explains how the unit can be used to display peak gas readings of the four
target gasses and to display STEL and TWA readings for H2S and CO. It
covers important issues regarding combustible gas detection. It also
covers alarm indications and use of the aspirator adapter accessory.
Normal Operation
After you have powered up the Model GX-2001 and performed a demand
zero for the four target gasses following the instructions of the previous
section, “Start Up,” the Model GX-2001 is in Measuring Mode.
In Measuring Mode, the battery level, time, and gas concentrations are
displayed on the LCD. The Model GX-2001 cycles through the four target
gases, starting with O2, then H2S, CO, and HC. Oxygen is displayed as a
percentage (%), H2S and CO as parts per million (ppm), and HC
(combustible gases) as a percentage of the lower explosive limit (% LEL).
Displaying Peak Readings
You can display peak readings of the four target gasses when the Model
GX-2001 is in Measuring Mode using the MODE/POWER and DISP
buttons. With oxygen, you can display both peak and minimum readings.
1. Make sure the Model GX-2001 is in Measuring Mode. The four target
gasses should be displaying in sequential order on the LCD.
2. Press the MODE/POWER button once to put the Model GX-2001 in
Peak Reading Mode. A small peak (minimum for O2) symbol is
displayed in the lower left corner of the LCD.
3. Press the DISP button to cycle through the four target gases. The peak
readings of these gasses are displayed on the LCD.
NOTE: Oxygen has both a peak and minimum reading.
O2
20.9
21:19
%
Target gas Battery
charge
Gas concentration Time
Figure 2: LCD in Measuring Mode

Model GX-2001 Operator’s Manual Operation • 17
4. To return to Measuring Mode, normal operation, press and release the
MODE/POWER button until the normal screen is displayed.
NOTE: While in Peak Reading Mode, if no control button has been
pushed for about 15 seconds, the Model GX-2001 returns to
Measuring Mode automatically.
Displaying STEL and TWA Readings
With the Model GX-2001, you can display STEL and TWA readingsfor H2S
and CO. STEL is an acronym for short-term exposure limit, and it shows
the average reading for H2S and CO during the last 15 minutes. TWA is an
acronym for time-weighted average, and it shows the average reading for
H2S and CO during the last eight (8) hours. If eight (8) hours has not
elapsed since the last time the STEL/TWA readings were cleared, the TWA
is still calculated over eight hours, withthe missing time assigned a zero (0)
value for the readings.
1. Make sure the Model GX-2001 is in Measuring Mode. The four target
gasses should be displaying in sequential order on the LCD.
2. Using the DISP button, display either H2S or CO on the LCD.
3. With either H2S or CO displayed on the LCD, press the MODE/POWER
button twice to put the Model GX-2001 in STEL Reading Mode. “STEL”
displays next to the time reading on the LCD.
4. To put the Model GX-2001 in TWA Reading Mode, press the MODE/
POWER button again while the unit is in STEL Reading Mode. “TWA”
displays next to the time reading on the LCD.
5. Press the DISP button to toggle between the TWA reading for H2S and
CO.
6. To return to Measuring Mode, normal operation, press the MODE/
POWER button.
NOTE: While in STEL or TWA Reading Mode, if no control button has
been pushed for about 15 seconds, the Model GX-2001 returns to
Measuring Mode automatically.

18 • Operation Model GX-2001 Operator’s Manual
Combustible Gas Detection
There are two issues that must be considered when checking for
combustible gas.
• The combustible sensor will respond to any combustible gas. The
standard calibration for the GX-2001 combustible channel is to
methane (CH4). If the instrument is to be used to monitor for a different
combustible gas, such as hexane or propane, it should be calibrated to
that gas.
The table below lists the conversion factors for several hydrocarbon
gasses if the GX-2001 is calibrated to methane. To use this table,
multiply the display reading on the combustible gas channel by the
factor in the appropriate row to obtain the actual gas concentration. For
example, if you are detecting pentane and the display reads 10% LEL
on the combustible channel, you actually have 10% LEL x 1.35 = 13.5%
LEL pentane present.
Table 3: LEL Hydrocarbon Conversions
Gas LEL Conversion Factor(Methane
Calibration) Gas LEL Conversion
Factor (Methane
Calibration)
Acetone 1.92 Iso Butane 1.56
Acetylene 2.00 MEK 1.92
Benzene 2.00 Methane 1.00
Ethane 1.25 Methanol 1.65
Ethanol 1.75 Pentane 1.35
Ethylene 1.20 Propane 1.52
Heptane 1.92 Propylene 1.33
Hexane 1.65 Toluene 2.00
Hydrogen 1.00 Xylene 0.93
IPA 2.50

Model GX-2001 Operator’s Manual Operation • 19
• The GX-2001 provides the combustible sensor with some protection
against exposure to high levels of combustible gas. It does this by
turning off the combustible sensor power temporarily when it
determines that an over scale (more than 100% LEL) concentration of
combustible gas is present that may damage the sensor. Nevertheless,
concentrations of combustible gas of more than 100% LEL can still
affect the zero level or calibration of the combustible sensor if the
concentration is high enough.
CAUTION: Do not expose the combustible sensor to high concentrations
of combustible gas such as that from a butane lighter.
Exposure to high concentrations of combustible gas may
adversely affect the perform of the sensor.
Alarms
This section coversalarm indications, including multiple alarms and trouble
alarms. It also tells you how to reset the Model GX-2001 after an alarm has
occurred and how to respond to an alarm condition.
NOTE: False alarms may be caused by radio frequency (RF) or
electromagnetic (EMI) interference. Keep the GX-2001 away from
RF and EMI sources such as radio transmitters or large motors.
Alarm Indications
The Model GX-2001 will sound an alarm and the unit will vibrate when one
of the target gas concentrations rises above the first alarm point, or in the
case of oxygen, falls below the low point alarm setting for that gas.
The Model GX-2001 also sounds an alarm and vibrates when the second
alarm point is reached for HC, CO, and H2S, when the concentration of
oxygen rises above 23.5% in the monitoring area, and when the STEL and
TWA alarm points are reached for CO and H2S.
When a trouble condition occurs, such as a sensor failure or low battery
charge, the unit will also sound an alarm but it will not vibrate.

20 • Operation Model GX-2001 Operator’s Manual
The table below summarizes the types of alarms produced by the Model
GX-2001.
Table 4: Alarm Types and Indications
Alarm Type LCD Indications Other Indications
Alarm 1
Concentration of gas
rises above the first
alarm point, or for O2,
falls below the low
point setting.
• Name of gas
displayed.
• Alarm light flashes
once per second.
• Back light turns on.
• Gas reading
flashes.
Pulsing tone once
per second
Unit vibrates once
per second
Alarm 2
Concentration of gas
rises above second
alarm point, or for O2,
rises above the high
point setting.
• Name of gas
displayed.
• Alarm light flashes
twice per second.
• Back light turns on.
• Gas reading
flashes.
Pulsing tone twice
per second
Unit vibrates twice
per second
TWA or STEL
Concentration of CO
or H2S risesabovethe
TWA or STEL alarm
point setting.
• Name of gas
displayed.
• Alarm light flashes
once per second.
• Back light turns on.
•TWAorSTEL
blinking.
Pulsing tone once
per second
Unit vibrates once
per second
Over Range • Name of gas
displayed.
• Gas reading
replacedbyblinking
brackets.
• Alarm light flashes.
• Back light turns on.
Pulsing tone once
per second
Unit vibrates once
per second
Low Battery Warning • Battery icon
flashes. None
Dead Battery Alarm • Gas reading
replaced by FAIL.
• Battery icon
flashes.
Double Pulsing Tone
(two pulses in quick
succession)