| PHOTOACOUSTIC INFRARED MULTI-GAS ANALYZER Model 1301 |
DESCRIPTION
This analyzer is a Fourier Transform Infra Red (FTIR) spectrometer. Its detection
principle is based on photoacoustic absorption using Innova's patented photoacoustic
measurement chamber. Its rugged and stable optical design, coupled with its
high selectivity, flexibility, and sensitivity, make it ideal for all kinds
of on-site measurements, both qualitative and quantitative.
ON-SITE OPERATION
The analyzer is well suited for use on-site. It can be easily transported with
little effect on the alignment of the optical system, and can be powered by
a mobile battery-power pack in the absence of a mains supply. No re-calibration
is needed when it is moved, just a short warm-up time if the power is disconnected.
GRAPHICS SCREEN
The user can see measurement results on-site, as the analyzer has a built-in
graphics screen. Absorption spectra, concentration curves, or tables of concentrations
can be displayed.
DISK DRIVE
The user can load measurement setups, or store results at the press of a button
using the built-in disk drive. When monitoring, results can be automatically
written to a specified disk file, allowing unattended measurement to continue
for up to 20 days (with 7 filters defined and 1 measurement cycle per minute).
Results can then be simply printed or plotted out from the disk at a later stage.
EASE OF USE
The graphics-screen displays, together with the hard keys on the front panel,
provide the basic "user interface" for operating the analyzer. A mouse
is supplied and can be used instead of the hard keys – making operation
faster. The user-friendly text and graphics, combined with the dedicated Help
Disk, enable non-technical personnel to make measurements.
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FEATURES:
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APPLICATIONS Quantitative
analysis measurements on site Industrial-process
monitoring Industrial
hygiene using air-quality measurements To
ensure health and safety in the workplace Detecting
accidental gas releases Analysis
measurements at landfill sites Analysis
measurements at hazardous-waste sites |
VERSATILITY
The Type 1301 can both analyze and monitor gases. Two different measurement
modes are included; spectrum-mode for analysis and concentration-mode for monitoring.
Measurements can be made either by using the four Measurement Control hard keys
on the front panel, or remotely by computer over one of the two interfaces.
MEASUREMENT SETUPS
Up to 40 different setups, to suit 40 different measurement situations, can
be defined and stored in a catalogue in the internal memory. In each of these
setups, the user specifies the combination of gases to be measured (up to 7
per setup) and defines how the measurement will be made.
Measurement Setups can also be stored and recalled as files from the analyzer's
disk drive.
GAS SETUPS
Up to 100 different setups, to measure 100 different gases, can be defined and
stored in a catalogue in the internal memory. In each of these setups, the user
specifies how a single gas will be measured e.g. filter limits, instantaneous
and average alarm levels, and molecular weight. Up to 7 Gas Setups can be included
in each Measurement Setup Gas Setups can also be stored and recalled as files
from the analyzer's disk drive. They can be either user-defined setups, or setups
defined by Innova which are stored in reference files on a reference date disk.
SYSTEM SETUPS
Up to 10 different setups can be defined and stored in a catalogue in the internal
memory. In each of these setups, the user specifies a variety of system parameters
e.g. for plotting and printing, for communicating via the two interfaces, setting
the internal clock, enabling or disabling self-tests.
System Setups can also be stored and recalled as files from the analyzer's disk
drive.
SEQUENCES
Sequences can be used to program the analyzer's operation and leave it to work
unattended. Each sequence can consist of up to about 50 command lines, which
are selected from a basic set of 18 commands, e.g. "Single" and "Plot".
The user can determine in advance which type of measurements are made; when
they will start and for how long they continue. There are commands which instruct
the analyzer to plot or print measurement results, or store them to disk, recall
files from disk, and change which setups are active. A sequence can recall other
sequences from disk during execution, allowing other sequences to be used like
subroutines. Up to 5 different control sequences can be defined in the internal
memory. Sequences can otherwise be stored and recalled as files from the analyzer's
disk drive.
SELECTIVITY
The analyzer can, in principle, measure almost any gas which is able to absorb
infrared light within the region
4000 cm-1 to 650 cm-1. Detection limits are gas-dependent, but lie typically
in the range of 0.1 to 10 ppm (parts per million).
The user can define up to 3 filter bands in memory for each gas to be measured.
These filter bands are applied to the measured absorption spectrum as integration
limits in order to determine the total absorption by the gas.
This is used to determine its concentration. In addition, each of the three
filter bands can be "weighted" differently so that their contributions
to the absorption are different. The user can directly define the limits on
the characteristic absorption spectrum (reference spectrum) of the gas which
can be read from a reference data disk and displayed on the screen. The frequency
range of the analyzer is large enough (4000 cm-1 to 650 cm-1) to easily identify
unique absorption peaks for each gas. Results are compensated for background
signal, temperature variations, and variations in infrared energy in the measurement
chamber.
CALIBRATION
Before any measurements are made, it is recommended that the analyzer is zero-spectrum
calibrated in order to compensate for the background signal in the chamber.
This is the signal measured when no absorbing gas is present. This means making
a calibration measurement with dry "zero-gas" (one which does not
absorb infrared light) e.g. pure nitrogen. This calibration is always done "directly:
by connecting a gas supply to the air inlet of the analyzer. If gas concentrations
are to be measured, the analyzer must also be span-calibrated for each of the
measurement-gases. Span calibration can be done "directly" by connecting
a fixed and known concentration of gas to the air inlet, or it can be done "indirectly"
by loading a reference spectrum (which replaces the result of a "direct"
calibration measurement) from a reference data disk. An indirect span-calibration
removes the need for a gas supply and all the associated hardware. Though it
is less accurate, the accuracy of an indirect calibration is sufficient for
many purposes. During indirect calibration, the user can also choose to load
an entire gas setup, which is stored with the reference spectrum on disk. This
removes the need for the user to define filter limits. The Standard Reference
Data Disk is supplied with the analyzer.
MEASUREMENT RESULTS
The measurement results are based directly on the amount of infrared light absorbed
by the gas sample, which gives a very high degree of accuracy and low drift.
Extensive averaging of results can be used to obtain greater accuracy; each
sample can be scanned up to 200 times. For example, scanning the sample 16 times
instead of just once gives an improvement in the Signal/Noise ratio by a factor
of four. The minimum measurement time for a single gas sample, including the
time for flushing the chamber, is around 65 s. Results are displayed in three
different ways:
Absorption spectra (for analysis) Absorption is shown in the region 2.5 to 15.4
um (4000 to 650 cm-1). In addition to spectra recorded during measurements,
reference spectra recorded during calibrations can also be displayed. Spectra
can be subtracted from each other and compared. All spectra are displayed at
the internal reference conditions i.e. 1013 mbar and 293K. Table of concentrations
(for monitoring) The table shows an overview of concentration levels, for all
measured gases at the same time. Maximum, minimum, average and instantaneous
values are displayed.
"Time History" concentration curves (for monitoring) The curves show
how the concentration level varies with time for a single measured gas. The
displayed concentrations are normalized to one of three user-specified temperatures
and 1013 mbar.
REMOTE OPERATION
The analyzer can be remotely controlled by a personal computer (PC) via the
IEEE-488 or the RS-232 interface. A PC can in this way be used to remotely control
complete measurement systems. These may typically include a printer and plotter
to make hard copies of results.
DATA HANDLING
The analyzer's built-in disk drive enables the user to retrieve and store large
amounts of data efficiently. All types of measurement data, hard copy data and
setups can be stored in disk files for later use.
WARNING
The Type 1301 must not be placed in areas with flammable gases/vapors in explosive
concentrations, or be used to measure explosive concentrations of these gases.
Also, measurement of certain corrosive gases, or a very high concentration of
water vapor, could result in damage to the analyzer. Ask your local Innova representative
for further information.
MEASUREMENT
SYSTEM OF THE 1301
Measurement Cycle
1-The pump draws air from the sampling point through 2 air-filters to flush
out the "old" air in the measurement system and replace it with a
"new" air sample.
2-The "new" air sample is hermetically
sealed in the analysis cell by closing the inlet and outlet valves.
Broad band light from an infrared source is modulated to produce a time-varying
signal by passing it through a modified Michelson Interferometer.
The beamsplitter and its 2 associated
platform mirrors are all mounted in fixed positions on a single platform which
rotates relative to the base through a very small angle (about 1°) which
continuously varies the path length of the beam to produce the interferogram.
This represents a single double-sided "scan" of the sample and takes
around 13 seconds.
Using this optical design, the
interferometer is highly stable and immune from the effects of external disturbance.
A laser diode and detector provide a reference system, which is used to trigger
and synchronize sampling of the interferograms produced, the laser signal taking
the same path as the IR signal.
The infrared light reflected from the interferometer output mirror enters the
measurement chamber. Here it is selectively absorbed by the gas sample, which
causes the temperature of the gas to fluctuate.
This produces corresponding pressure fluctuations within the chamber i.e. an
acoustic signal. The frequencies of the acoustic signal depend on the wavelengths
of the light absorbed by the gases present in the sample.
An intensity detector mounted in the chamber measures the variations in intensity
of the infrared light. This produces the signal which is used for energy normalization
of all measured spectra.
The photoacoustic signal is measured by the 2 microphones mounted on the chamber
walls to produce an electrical signal proportional to the amount of absorption
that has occurred.
The electrical signal is then filtered and sampled (converted from an analogue
to a digital signal) and Fourier transformed to produce an absorption spectrum.
User-defined filter bands determine individual concentration values. These are
obtained from the spectrum by integrating between the chosen limits for the
filter bands and applying a conversion factor for the ga
MEASUREMENT TECHNIQUE:
Fourier Transform Infra Red (FTIR) spectroscopy. The Type 1301 measures the
absorption of infrared light by the gas sample photoacoustically.
MEASUREMENT TIME: Dependent on the length of the sampling
tube and the amount of averaging (no. of scans). If the tube is less the 1m,
then the total measurement time for a single gas-sample (from starting the pump
to displaying results) is down to around 65 seconds.
MEASUREMENT RANGE:
Detection Limit: Depending on the gas's absorption in the chosen frequency band,
on the filter configuration, and on the no. of scans per sample. It typically
ranges from 10-1 parts per million (ppm) to 10 ppm*.
Dynamic Range: Dependent on the amount of averaging (no. of sans) and the gas
itself. Typically four orders of magnitude, i.e. 10,000 times the detection
limit*. Expandable with external software.
Resolution: Dependent on the type of apodization selected; using Hanning it
is 15 cm-1, using Flat Top it is 10 cm-1
Wavenumbers: 4000 cm-1 to 650 cm-1
MEASUREMENT UNITS:
In mg/m3 or parts per million (ppm) normalized to a temperature entered by the
user and 1013 mbar ACCURACY:
Zero Drift: Typically equal to detection limit per 3 months
Repeatability: *Typically (sigma) n-1<1% of reading using concentrations
over 500 times detection limit
Range Drift: Typically.5% of reading per 3 months
Influence of pressure is equal to +0.1% of reading per mbar (compensated for
by entering ambient pressure)
Reference conditions:
Measured at 20° C, 1301 mbar, and relative humidity (RH): 60%
Measured at 20° C, and relative humidity (RH) of 60%
*Measured using 8 scans per gas sample
CALIBRATION:
Two types:
Span calibration
Zero-spectrum calibration
Span calibration can be done either by loading reference-spectra data from the
disk drive of the Type 1301, or directly by connecting supplies of gas to the
inlet of the Type 1301
Calibration is not usually needed more than 4 times per year
ERROR COMPENSATIONS:
Includes automatic compensation for interference due to:
Temperature fluctuations in the measurement chamber
Intensity fluctuations of the infrared light in the interferometer adjustment,
and absorption in the optical path outside the chamber
DATA STORAGE CAPACITY:
In RAM (Internal Memory)
Concentration Measurements: Over a 4 hour period, with 7 user-defined filters
in memory and a measurement sample interval of 1 minute
Spectra: 1 input spectrum (last measurement result) plus 5 stored measurement
spectra
Calibration data
On Disk:
Concentration Measurements: as for RAM (above), but it is able to store results
over a 480 hour period on each disk
Spectra: 224 absorption spectra can be stored on each disk. (limit on no of
files set by DOS)
Calibration Data
DISK DRIVE:
Disk Size: 3.5"
Capacity: 720 Kbytes (DD) or 1.44 Mbytes (HD)
COMPLIANCE WITH STANDARDS:
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Environmental
Analytical Systems
286 Mask Island Drive
Barry's Bay, Ontario, Canada K0J 1B0
Phone:
613 756 0101
Toll Free (Canada only):
1 800 427 8591
Fax: 613 756 0909
email: info@enviro-analytical.com
©Environmental Analytical Systems 2003
