gas & chemical co. ltd.
D E T E C T I O N
T E C H N O L O G Y
Leak Detection |
Plant Maintenance |
Metal Integrity |
Gas Monitoring |
Personnel Protection |
Using the CGT-501 for
What you should
know about the detector
IMPORTANT: The CGT-501 was designed to be non-quantitative and
non-selective. It is intended for the indication of the presence
of combustible and/or toxic gases and vapors by relative magnitude
only. Its primary purpose is to locate the source of a contaminant
gas or vapor and/or compare concentrations of a gas or vapor
relative to other locations.
About the CGT-501
Two types of CGT-501 units are available.
The Alkaline Battery Model (CGT-501AK) which comes
with 4 AA Alkaline Batteries installed. The 501AK is
recommended when the detector is seldom used or when storing
the detector for long periods of time. One of the main
advantages of alkaline batteries is that they hold their
charge for long periods of time when not in use. When the
detector is needed, the alkaline batteries have plenty of
stored power and are ready to operate.
The Nickel Cadmium Battery Model (CGT-501NK) which
comes with a ni-cad battery pack that can be recharged over
500 times if properly maintained and recharged according to
manufacturers specifications. The 501NK is recommended when
the detector is used frequently (daily or several times a
week). Being able to recharge these batteries keeps down the
cost of battery replacement.
Both battery units are 6 volts DC power sources and allow
the unit to perform best when fully charged.
Several accessories are available for the CGT-501 which can
help you in performing several of the more difficult tests
and checks that most home inspections require.
See Accessories Available.
3. Sensitivity Levels
The CGT-501 has three sensitivity levels adjustable by a
three position sensitivity switch located inside the unit.
Access to this switch is made by removing the three slotted
screws on the back of the CGT-501 and locating the switch in
the upper right hand side of the unit. The red dot on the
switch indicates the most sensitive setting. The medium
setting on the unit (middle position) is the most popular
setting for the home inspection application. It allows
enough sensitivity to locate the small ppm levels of Carbon
Monoxide in a range that is of concern and also allows
sensing of the Methane and Propane Combustible vapors in
very low %LEL concentration.
4. The Sensor
The sensor is a solid state tin dioxide substrate deposited
on a ceramic tube. Through its center is a coiled heater
filament which keeps the sensor heated at the proper
operational temperature which assures better accuracy during
detection. The sensor responds well to most combustible and
many toxic gases and vapors, although it cannot distinguish
between the different gases or vapors. It can provide a
quantitative indication when only one gas or vapor is
present. The sensor is intended to be good for over 10,000
exposures. The sensor cannot be ruined by over exposure to
high gas concentrations it detects. The flashback arrestor
operates effectively to prevent flame propagation if
ignition inside the sensor should occur, but the sensor is
not intended for hazardous locations. IMPORTANT: the
temperature of the gas or vapor sample being detected and
the ambient wind conditions can significantly affect the
accuracy and reliability of the output to the meter signal.
When the CGT-501 has not been used in the last five days
The start up sequence is very important in assuring the most
accuracy and reliability out of the CGT-501. It is
recommended that you turn the unit on 5-15 minutes before
starting detection. The initial warm-up time is lengthened
to allow the tin dioxide sensor to burn off all the
oxidation which has accumulated on the sensor. Continuous
zero adjustments will be needed in order to maintain a zero
reading on the meter face.
Keep the sensor head at constant temperature
during detection and warm-up so erroneous readings will not
be made due to large temperature swings delivered or
diffused to the sensor head by the sample. Watch out for
significant temperature changes when testing areas such as
flues, stacks, registers, etc. and when entering a new room
TIP: Capture samples of the gas or
vapor being tested in a container (such as a plastic bag or
plastic or glass bottle) and insert the CGT-501 sensor into
the opening of that container. This will help eliminate
significant temperature differences and air flow rate
differences which have a large effect on the output to the
meter. Re-adjustments of the zero knob may be required to
re-zero the background reading observed.
Learn basic information about the gases or vapors you are
trying to detect
This will greatly increase your success rate.
Characteristics such as vapor density (heavier or lighter
than air), toxicity levels and/or lower explosion levels(LEL),
dispersion characteristic of a gas or vapor, can mean the
difference between successful detection or erroneous
For example if you know that:
• Carbon Monoxide is slightly lighter than air and when
heated will it will rise. Detection can be made at ceiling
levels for this gas.
• The LEL of Propane is 2.1% by volume or 21,000ppm.
Detection of a small leak can be done in the 100-500 ppm
range. This range is easily obtained in medium sensitivity
on the CGT-501. Propane is 1.6 times heavier than air and
should be detected closer to the ground or floor for the
Approximate meter needle indications
The following chart gives approximate meter needle
indications on a CGT-501 when concentrations of the listed
gases or vapors are present. NOTE: Tests were conducted with
detectors with fully charged batteries.
CGT-501 DETECTABLE LEVELS in PARTS PER MILLION (ppm)
||From 3 to 20
||From 10 to 75
||From 30 to 200
||From 5 to 25
||From 1 to 25
||From 50 to 200
||From 100 to 2000
|| From 10 to 75
|| From 50 to 500
||From 200 to 2000
Copyright ©2020 American Gas & Chemical Co. Ltd., 220 Pegasus Avenue, Northvale, N.J. 07647-1977, U.S.A. 1-800-288-3647 or 1-201-767-7300 * fax: 201-767-1741