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TGA100
User Manual
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Campbell Scientific TGA100 User Manual

TGA100 TRACE GAS ANALYZER
USER AND REFERENCE MANUAL
LAST REVISION: 2 August 2004
COPYRIGHT © 1992 - 2004, CAMPBELL SCIENTIFIC, INC.
2

TABLE OF CONTENTS

1 OVERVIEW 12
1.2.1 Optical System 13
1.2.2 Laser Scan Sequence 14
1.2.3 Concentration Calculation 15
1.3 Trace Gas Species Selection 15
1.5 User Interface 16
1.6 Micrometeorological Applications 17
1.6.1 Eddy Covariance 17
1.6.2 Flux Gradient 18
1.6.3 Site Means 19
1.6.4 Absolute Concentration / Isotope Ratio Measurements 20
1.7 Specifications 21
1.7.1 Measurement Specifications 21
1.7.2 Physical Specifications 22
2 INSTALLATION 23
2.2 TGA100 PC Installation 24
2.3.1 Startup Procedure 25
2.3.2 Shutdown Procedure 25
2.3.3 System Checks 26
3 TGA SOFTWARE 27
3.1 General 27
3.2 Startup 27
3.3 Main Menu 27
3
4
3.4.1 Screen Layout 29
3.4.2 Navigating and Editing 30
3.4.3 Run Mode 30
3.4.4 Dynamic Parameters 31
3.4.5 Detector Video 32
3.4.6 Functions 32
3.4.7 Graph Selections 32
3.4.8 Graph Display Limits 33
3.4.9 Quick Keys 33
3.5 Parameter Change Menu 35
3.5.1 Standard Parameter Screens 36
3.5.2 File Output Selection Screen 37
3.5.3 Analog Output Screen 38
3.5.4 Gradient and Site Means Screens 39
3.6 TGA Files 39
3.6.1 Parameter Files 39
3.6.2 10 Hz Concentration Data Files 40
3.6.3 Gradient (Delta Concentration) Files 40
3.6.4 Site Means Files 41
3.6.5 Housekeeping Data File 42
3.6.6 Header Files 43
3.6.7 User Messages 43
4 DETAILED SETUP INSTRUCTIONS 44
4.1 Configuring the System for a Specific Gas Species 44
4.1.1 Laser Selection 44
4.1.2 Reference Gas 44
4.1.3 Detectors 45
4.1.4 Air Gap Purge 46
4.1.5 Polyethylene Sample Cell Liner 46
4.2.1 Setting Parameters to Align a New Laser 49
4.2.2 Initial Alignment 49
4.2.3 Horizontal and Vertical Alignment 50
4.2.4 Focus Adjustment 51
4.2.5 Reference Detector Coalignment 51
5
6
4.3 Finding the Absorption Line 52
4.4 Laser Mapping 53
4.5 Optimizing Laser Parameters 55
4.5.1 Laser Temperature 55
4.5.2 Zero Current 58
4.5.3 High Current 59
4.5.4 Omitted Data Count 62
4.5.5 Laser Modulation Current 63
4.5.6 Laser Maximum Temperature and Laser Maximum Current 63
4.5.7 Laser Multimode Correction 63
4.6 Optimizing Detector Parameters 64
4.6.1 Detector Gain and Offset 64
4.6.2 Detector Temperature 65
4.6.3 Detector Linearity Coefficients 65
4.7 Calibration 66
5 SAMPLING SYSTEM CONTROL 67
5.1 GRADIENT MEASUREMENTS 67
5.1.1 Gradient Overview 67
5.1.2 Gradient Calculations 68
5.1.3 Real time display 70
5.1.4 Controlling Gradient Valve Assemblies 70
5.1.5 Controlling a Gradient Site Selection Assembly 72
5.1.6 Gradient Mode Parameters 74
5.1.7 Gradient Mode Setup 75
5.2 SITE MEANS MEASUREMENTS 80
5.2.1 Site Means Overview 80
5.2.2 Site Means Calculations 81
5.2.3 Real Time Display 83
5.2.4 Controlling a Site Means Sampling System 83
5.2.5 Site Means Parameters 84
5.3 MASTER/SLAVE OPERATION 85
5.3.1 Master/Slave Setup 85
5.3.2 Master/Slave Operation 86
5.3.3 Shift and Omit Samples 86
7
8
6 EDDY COVARIANCE MEASUREMENTS 86
6.1 Overview 86
6.2 Flow Rate and Tubing Size 88
7 AUXILIARY INPUTS AND OUTPUTS 90
7.1 Reading Data from a CSAT3 Sonic Anemometer 90
7.2 Reading Data from a CR9000 90
7.3 Sending Concentration Data to a CR9000 91
7.6 Analog Outputs 92
7.7 Digital Outputs 93
8 TGA100 OPTIONS 94
8.1 Laser Cooling 94
8.1.1 LN2DEWAR TGA100 LN2 Laser Dewar 94
8.1.2 CRYODEWAR TGA100 Laser Cryocooler System 94
8.2 Lasers 95
8.3 TGAHEAT Temperature Controller 95
9 TGA100 ACCESSORIES 96
9.1 TGA100 Insulated Enclosure Cover 96
9.2 Dewar Evacuation System 96
9.3 Sample Vacuum Pump 96
9.4.1 General Description 97
9.4.2 Theory of Operation 98
9.4.3 Installation Instructions 98
9
10
10 TROUBLESHOOTING 102
10.1 Fiber Optic Diagnostics 102
APPENDIX A. OPTIONS FOR FILE SAVE AND REAL TIME DISPLAY 104
APPENDIX B: DEFAULT PARAMETER FILE 108
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1 OVERVIEW
The TGA100 Trace Gas Analyzer measures trace gas concentration in an air sample using tunable diode laser absorption spectroscopy (TDLAS). This technique provides high sensitivity, speed, and selectivity. The TGA100 is a rugged, portable instrument designed for use in the field. It can measure one of a large number of gases by choosing appropriate lasers and detectors. It incorporates several features that make it ideal for measuring fluxes of trace gases using gradient or eddy covariance techniques. A vacuum pump continuously pulls the air sample through the analyzer, which measures the concentration of the trace gas at a 10 Hz rate. The TGA computer provides the user interface; controlling the analyzer, and calculating, displaying, and storing data in real time.
1.1 System Components
Figure 1-1 These system components include:
illustrates the main system components as well as additional equipment needed to operate the TGA100.
• TGA100 Analyzer: The analyzer optics and electronics, mounted in an insulated fiberglass enclosure.
• TGA100 PC: A desktop computer, supplied as part of the TGA100.
• Fiber optic cable (7737-L): Connects the TGA100 analyzer to the TGA100 PC.
• Sample Intake (15838 shown): Filters the air sample and controls its flow rate.
• Sample pump (RB0021-L shown): Pulls the air sample and reference gas through the analyzer at low pressure.
• Suction hose (7123): Connects the analyzer to the sample pump. Supplied with RB0021 sample pump.
• Reference gas: tank of reference gas, with pressure regulator (supplied by user).
• Reference gas connection (15837): Flow meter, needle valve, and tubing to connect the reference gas to the
analyzer.
TGA100 Analyzer
TGA100 PC
Fiber Optic Cable
12
Sample Intake
Reference Gas Connection
Reference Gas
Sample Pump
Figure 1-1. TGA100 System Components
Suction Hose
1.2 Theory of Operation

1.2.1 Optical System

The TGA100 optical system is shown schematically in . The optical source is a lead-salt tunable diode laser that operates between 80 and 140 K, depending on the individual laser. Two options are available to mount and cool the laser: the TGA100 LN2 Laser Dewar and the TGA100 Laser Cryocooler System. Both options include a laser mount that can accommodate one or two lasers. The LN2 Laser Dewar mounts inside the analyzer enclosure. It holds 10.4 liters of liquid nitrogen, and must be refilled twice per week. The Laser Cryocooler System uses a closed-cycle refrigeration system to cool the laser without liquid nitrogen. It includes a vacuum housing mounted inside the analyzer enclosure, an AC-powered compressor mounted outside the enclosure, and 3.1 m (10 ft) flexible gas transfer lines.
Reference detector
Figure 1-2
Figure 1-2. Schematic Diagram of TGA100 Optical System
The laser is simultaneously temperature and current controlled to produce a linear wavelength scan centered on a selected absorption line of the trace gas. The IR radiation from the laser is collimated and passed through a 1.5 m sample cell, where it is absorbed proportional to the concentration of the target gas. A beam splitter directs most of the energy through a focusing lens to the sample detector, and reflects a portion of the beam through a second focusing lens and a short reference cell to the reference detector. A prepared reference gas having a known concentration of the target gas flows through the reference cell. The reference signal provides a template for the spectral shape of the absorption line, allowing the concentration to be derived independent of the temperature or pressure of the sample gas or the spectral positions of the scan samples. The reference signal also provides feedback for a digital control algorithm to maintain the center of the spectral scan at the center of the absorption line. The simple optical design avoids the alignment problems associated with multiple-path absorption cells. The number of reflective surfaces is minimized to reduce errors caused by Fabry-Perot interference.
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1.2.2 Laser Scan Sequence

The laser is operated using a scan sequence that includes three phases: the zero current phase, the high current phase, and the modulation phase, as illustrated in Figure 1-3. The modulation phase performs the actual spectral scan. During this phase the laser current is increased linearly over a small range (typically +/- 0.5 to 1 mA). The laser’s emission wavenumber depends on its current. Therefore the laser’s emission is scanned over a small range of frequencies (typically +/- 0.03 to 0.06 cm
-1
).
During the zero current phase, the laser current is set to a value below the laser’s emission threshold. “Zero” signifies the laser emits no optical power; it does not mean the current is zero. The zero current phase is used to measure the detector’s dark response, i.e., the response with no laser signal.
The reduced current during the zero phase dissipates less heat in the laser, causing it to cool slightly. The laser’s emission frequency depends on its temperature as well as its current. Therefore the temperature perturbation caused by reduced current during the zero phase introduces a perturbation in the laser’s emission frequency. During the high current phase the laser current is increased above its value during the modulation phase to replace the heat “lost” during the zero phase. This stabilizes the laser temperature quickly, minimizing the effect of the temperature perturbation. The entire scan sequence is repeated every 2 ms. Fifty consecutive scans are averaged and processed to give a concentration measurement every 100 ms (10 Hz sample rate).
Modulation Phase
High Current Phase
(Temperature
Stabilization)
(Spectral Scan)
Zero Current Phase
(Laser Off)
Omitted
Used in Calculation
2 ms
Figure 1-3. TGA100 Laser Scan Sequence
Laser Current
Detector Response
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1.2.3 Concentration Calculation

The reference and sample detector signals are digitized and averaged over 50 consecutive scans. The average reference and sample scans are then corrected for detector offset and nonlinearity, and converted to absorbance. A linear regression of sample absorbance vs. reference absorbance gives the ratio of sample absorbance to reference absorbance. The assumption that temperature and pressure are the same for the sample and reference gases is fundamental to the design of the TGA100. It allows the concentration of the sample, C
C
=
s
Where C
L
L
L
= concentration of reference gas, ppm
R
= length of the short reference cell, cm
R
= length of the short sample cell, cm
S
= length of the long sample cell, cm
A
, to be calculated by:
S
))()((
DLC
RR
AS
)1(
DLL
−+
D = ratio of sample to reference absorbance
1.3 Trace Gas Species Selection
The TGA100 can measure gases with absorption lines in the 3 to 10 micron range, by selecting appropriate lasers, detectors, and reference gas. Lead-salt tunable diode lasers have a limited tuning range, typically 1 to 3 cm
-1
within a continuous tuning mode. In some cases more than one gas can be measured with the same laser, but usually each gas requires its own laser. The laser dewar has two laser positions available (four with an optional second laser mount), allowing selection of up to four different species by rotating the dewar, installing the corresponding cable, and performing a simple optical realignment.
The standard detectors used in the TGA100 are Peltier cooled, and operate at wavelengths up to 5 microns. These detectors are used for most gases of interest, including nitrous oxide (N Some gases, such as ammonia (NH
), have the strongest absorption lines at longer wavelengths, and require the
3
O), methane (CH4), and carbon dioxide (CO2).
2
optional long wavelength, liquid nitrogen-cooled detectors. These detectors operate to wavelengths beyond 10 microns. They require filling with liquid nitrogen once each day.
A prepared reference gas having a known concentration of the target gas must flow through the reference cell. The beam splitter directs a small fraction of the laser power through the reference cell to the reference detector. This gives a reference signal proportional to the laser power, with the spectral absorption signature of the reference gas. The reference signal provides a template for the spectral shape of the absorption feature, allowing the concentration to be derived without measuring the temperature or pressure of the sample gas, or the spectral positions of the scan samples.
1.4 Dual Ramp Mode
The TGA100 can be configured to measure two gases simultaneously by alternating the spectral scan wavelength between two nearby lines. This technique requires that the two absorption lines be very close together (within about 1
-1
), so it can be used only in very specific cases. The dual ramp mode is used to measure isotope ratios in carbon
cm dioxide or water by tuning each ramp to a different isotopomer.
The dual ramp mode may also be used to measure some other pairs of gases, such as carbon monoxide and nitrous oxide, or nitrous oxide and methane, but the measurement noise will be higher than if a single gas is measured. For measurements of a single gas, the laser wavelength is chosen for the strongest absorption lines of that gas. Choosing a laser that can measure two gases simultaneously involves a compromise. Weaker absorption lines must be used in order to find a line for each gas within the laser’s narrow tuning range.
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1.5 User Interface
The TGA100 includes a computer that provides the user interface. It displays the data in real time, allows the user to modify control parameters, and saves data to the hard disk. The real time graphics screen is presented in . In
Figure 1-4 the upper left corner is a box which displays the TGA software version, the laser and detector temperatures, and the time. Beneath the time and temperature display is a blank area used for information and error message display. The rest of the top of the screen has five menu columns: run mode, dynamic parameters, detector video, special function enable/disable, and graph selections.
Figure 1-4. Real Time Graphics Screen
In the middle of the screen are graph 1 and graph 2, used to display certain user-selectable variables. This example shows N
Graph 3 is located at the bottom-center of the screen, and is also used to display user-selected variables. In this example graph 3 shows the sample cell pressure.
At the bottom left corner of the screen are two high speed graphic windows that show the raw reference (REF) detector signal and the raw sample (SMP) detector signal, scaled to match the analog-to-digital converter (ADC) input range.
At the bottom right corner of the screen are two more high speed graphic windows that display processed reference and sample signals. The user may select the type of data to display in these windows using the Detector Video menu or the Quick Keys. The number displayed at the top of these windows is either the transmittance or the absorbance of the center of the spectral scan, depending on the display mode selected. All four of the high-speed graphic windows have three vertical dashed lines. These lines show the center of the spectral scan and the range of data actually used to calculate concentration.
O concentration in graph 2 and laser temperature in graph 2.
2
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1.6 Micrometeorological Applications
The TGA100 is ideally suited to measure fluxes of trace gases using micrometeorological techniques. In addition to its rugged design that allows it to operate reliably in the field with minimal protection from the environment, it also incorporates several hardware and software features to facilitate these measurements.

1.6.1 Eddy Covariance

The TGA100's sample rate, frequency response, sensitivity and selectivity are optimized for measuring trace gas fluxes using the eddy covariance (EC) method. It is designed to collect three-dimensional wind data from a CSAT3 sonic anemometer while synchronously measuring trace gas concentration. Figure 1-5 illustrates a typical EC application. The sonic anemometer and air sample intake are mounted on the measurement mast. Tubing connects the air sample intake to the inlet of a PD1000 sample air dryer, which filters and dries the air sample. A needle valve at the outlet of the PD1000 sets the sample flow rate, typically to approximately 15 slpm. The TGA100 analyzer is located near the base of the measurement mast to minimize the length of sample tubing. This avoids the attenuation of high frequencies in the concentration data that can be caused by excessive tubing length. The TGA100 PC requires shelter from the environment, but can be located up to 500 m (1650 ft) away from the TGA100 analyzer, connected by fiber optic cable. The sample pump requires minimal shelter and can be located up to 90 m (300 ft) away from the analyzer, connected by the suction hose. The CSAT3 connects to the TGA analyzer by way of a TL925 serial interface module, which can be mounted inside the analyzer enclosure for protection from the environment.
CSAT3 Cable
Figure 1-5. Example Eddy Covariance Flux Application
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1.6.2 Flux Gradient

The TGA100 also supports the measurement of trace gas fluxes by the gradient method. The TGA100 automatically controls gradient switching valves and computes the mean concentration at each of the two intake heights. Timing parameters are entered by the user to control the gradient valves, typically switching between intakes every 5 to 20 s. The results are displayed on the TGA100 PC in real-time and stored on the hard disk.
Figure 1-6 measurement mast. Tubing connects each intake assembly to a gradient valve assembly that selects one of the intakes at a time. The air sample from the selected intake flows through the PD1000 sample air dryer, which filters and dries the air sample. A needle valve at the outlet of the PD1000 sets the sample flow rate, typically 5 to 10 slpm. Tubing connects the outlet of the dryer to the TGA100 analyzer, which may be located 200 m (650 ft) or more away. The TGA100 PC requires shelter from the environment, and can be located up to 500 m (1650 ft) away from the TGA100 analyzer, connected by fiber optic cable. However, for gradient applications the analyzer is normally positioned away from the intake mast, and the PC is placed near the analyzer for convenience. The sample pump requires minimal shelter and can be located up to 90 m (300 ft) away from the analyzer, connected by 1” ID suction hose.
This example shows a gradient flux measurement at a single site. However, the TGA100 can also support flux gradient measurements at multiple sites by installing intake assemblies, a gradient valve assembly, and a sample dryer at each site, and a site selection system near the analyzer. The site selection system connects one site at a time to the analyzer. The TGA100 controls the site selection system using timing parameters supplied by the user. Normally each site is measured for 15 to 30 min before switching to the next site.
illustrates a typical gradient application. Two intake assemblies are mounted at different heights on the
18
Figure 1-6. Example Gradient Flux Application

1.6.3 Site Means

The TGA100’s site means sampling mode is similar to the flux gradient mode in that it controls switching valves and calculates mean concentrations for each intake. The difference between the two sampling modes is that the gradient mode considers the sample intakes in pairs, switching several times between an upper and lower intake before moving to another site, but the site means mode considers all of the intakes as one group. It cycles through all of the intakes in sequence (up to 18 sites are supported). Applications for the site means mode include concentration profile measurements and trace gas flux measurements using the mass balance technique.
Figure 1-7
illustrates an eight-level vertical profile using the TGA100 site means mode. The eight intake assemblies are arranged vertically on a single measurement tower. These intake assemblies include a filter to remove particulates and a critical flow orifice to set the sample flow (typically less than 1 slpm). A separate tube connects each intake assembly to the site selection system, which selects one of the intakes at a time. All of the unselected intakes are connected through the bypass tube to the sample pump suction hose, keeping air flow at all times in all intake tubes. The flow from the selected intake goes through a sample air dryer to the TGA100 analyzer. A second dryer is used to provide dry air to purge the sample dryer.
Sample
Intakes
Digital Control Cable
Site Selection Sampling
Sample
System
Purge Dryer
Sample Dryer
Sample
Dryer Purge
Bypass
Figure 1-7. Example Profile Application
19

1.6.4 Absolute Concentration / Isotope Ratio Measurements

The TGA100 can be configured for highly accurate measurements of trace gas concentrations by performing frequent calibration. The TGA100 has a small offset error caused by optical interference. This offset error changes slowly over time, with a standard deviation roughly equal to the short-term noise. Offset errors have little effect on flux measurements by either the gradient or eddy covariance technique, but may be important in other applications. For measurements of absolute trace gas concentration, the offset error can be removed by switching between a nonabsorbing gas (e.g. nitrogen) and the sample, using the gradient mode of operation.
Applications such as isotopic ratio measurements require the highest possible accuracy. This is achieved using a frequent two-point calibration to correct for drift in the instrument gain and offset. High accuracy requires the flow rate for the calibration gases to be the same as for the sample air. Even though the sampling system can be designed so that calibration gases flow only when they are used, frequent calibration (every few minutes) consumes a large amount of calibration gas if high flow rates are used. The site means sampling mode is normally used because it works well at low flow rates.
Figure 1-8
illustrates a typical CO two intakes connected to calibration tanks. A tank of nitrogen or CO purge the air gap between the laser dewar and sample cell. This purge is required for CO because of the high ambient concentration of CO
isotope application. It is similar to the site means example above, but it also includes
2
-free air is also shown connected to the analyzer to
2
isotope measurements
2
and the need for high accuracy.
2
Sample
Intakes
Digital Control Cable
Sample
Site Selection Sampling System
Purge Dryer
Sample Dryer
Purge
Sample
Dryer Purge
Bypass
Calibration tanks
20
Figure 1-8. Example CO2 Isotope Application
1.7 Specifications

1.7.1 Measurement Specifications

Sample Rate: 10 Hz
Averaging Period: 0.1 sec
Sample cell volume: 480 ml
Frequency Response (@ 4.8 liter/sec actual flow rate): 3 Hz
The TGA100 frequency response is determined by the averaging time (0.1 s) and the time for a new sample to fill the sample cell. The frequency response was measured at 14.4 slpm flow rate and 50 mbar sample pressure (4.8 actual l/s) by injecting 1 µl of N
O into the sample stream. The resulting time series and frequency response graphs are shown in
2
. Figure 1-9
4
3
2
1
Concentration (ppmv)
0
0.0
0.5
1.0
Time (sec)
1.5
2.0
1
0.1
Frequency Response
0.01
0.1
Frequency (Hz)
1
5
Figure 1-9. TGA100 Impulse Response (left) and Frequency Response (right)
The typical 10 Hz concentration measurement noise, given in , is calculated as the square root of the Allan variance with no averaging (i.e. the two-sample standard deviation. This is comparable to the standard deviation of the 10 Hz samples calculated over a relatively short time (10 s). The typical 30-minute average gradient resolution is given as the standard deviation of the difference between two intakes, averaged over 30 minutes, assuming typical valve switching parameters.
Table 1
Table 1. Typical Concentration Measurement Noise
Gas Wave number
(cm
-1
)
10 Hz Noise
(ppbv)
Nitrous Oxide N2O 2208.575 1.5 30
Methane CH4 3017.711 7 140
Ammonia NH3 1065.56 6 200
Carbon Monoxide CO 2176.284 3 60
Nitric Oxide NO 1900.08 13 260
Nitrogen Dioxide NO2 1630.33 3 60
Sulfur Dioxide SO2 1366.60 25 500
30-min Gradient
Resolution (pptv)
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Typical performance for isotope ratio measurements is given in delta notation. For example, the δ by:

13
C
δ
R
s
=−×

R

1 1000
VPDB
13
C for CO2 is given
where R
is the ratio of the isotopomer concentrations measured by the TGA100 (13CO2/12CO2) and R
s
standard isotope ratio (
13C/12
C). δ13C is reported in parts per thousand (per mil or ‰). The 10 Hz noise is the square
VPDB
is the
root of the Allan variance with no averaging. The calibrated noise assumes a typical sampling scenario: two air sample intakes and two calibration samples measured in a 1 minute cycle. It is given as the standard deviation of the calibrated air sample measurements.
Table 2. Typical Isotope Ratio Measurement Noise
Gas Isotope Ratio Wavenumber (cm-1) 10 Hz Noise (‰) Calibrated Noise (‰)
δ13C 2293.881, 2294.481 0.5 0.1 Carbon
Dioxide

1.7.2 Physical Specifications

Analyzer
Length: 211 cm (83 in)
Width: 47 cm(18.5 in)
Height: 55 cm (21.5 in)
Weight: 74.5 kg (164 lb)
Optional Cryocooler Compressor
Length: 31 cm (12 in)
Width: 45 cm (18 in)
Height: 38 cm (15 in)
Weight: 32 kg (71 lb)
Power Requirements
Analyzer: 90-264 Vac, 47-63 Hz, 50 W (max) 30 W (typical)
Optional Heater: 90-264 Vac, 47-63 Hz, 150 W (max)
PC: 115/230 Vac, 50/60 Hz, 150 W
Optional Cryocooler Compressor: 100, 120, 220, or 240 Vac, 50/60 Hz, 500 W
Optional sample pump (RB0021-L): 115 Vac, 60 Hz, 950 W (other power options are available)
18
O 2308.225, 2308.416 2.5 0.5
δ
δ18O 1500.546, 1501.188 2 0.5 Water
δD 1501.813, 1501.846 10 2.5
22
2 INSTALLATION
The basic components required to operate the TGA100 are shown in Fi . Other components, such as a sample air dryer, valves to switch between multiple intakes, calibration gases, etc. may also be required, depending on the user’s application. These optional components will be discussed in other sections.
gure 2-1
TGA100 Analyzer
TGA100 PC
Fiber Optic Cable
Reference Gas Connection
Suction Hose
Sample Intake
Reference Gas
Sample Pump
Figure 2-1. Basic Components Required for TGA100 Operation
2.1 Analyzer Installation
The TGA100 analyzer (the optics and electronics) is housed in an insulated fiberglass enclosure that allows it to operate in the open environment. However, if a tent or other shelter is not available, the optional TGA Temperature Controller and TGA Insulated Enclosure Cover are recommended. The analyzer must be placed on a stable surface. If placed on uneven ground, wooden blocks or other supports can be used under the two pairs of rubber feet near the ends of the enclosure. Older enclosures have a third pair of rubber feet in the center, but should be placed on blocks so that only the four feet on the ends are used.
The analyzer should be connected to other system components as follows:
1) Connect the vacuum exhaust outlet of the analyzer to the sample pump using 1" ID exhaust hose and hose clamps.
The sample pump must be able to pull the required flow rate at 75 mbar or less. The actual flow rate and pressure required will depend on the application. The RB0021, available from Campbell Scientific, has a capacity of 18 slpm at 50 mbar (15 slpm with 50 Hz power), and is adequate for most applications.
2) Connect the reference gas supply to the reference gas inlet on the end of the analyzer. The reference gas supply
should have an appropriate regulator, flow meter, and needle valve to supply approximately 10 ml/min. See section
4.1.2 for more details on the reference gas.
23
3) Connect the sample intake to the sample gas inlet. The sample intake should be filtered to remove particulates (10
µm maximum pore size) and should have an appropriate needle valve or fixed orifice to control the sample gas flow and pressure.
4) Connect power. For older units, connect a user-supplied, regulated 12 Vdc supply with at least 5 ampere capacity
to the system enclosure POWER IN connector. Use the supplied external cable (CSI PN 7987) with the red wire connected to +12 volts and the black wire to ground return. Newer units are supplied with an internal, universal­input power supply. Connect the power supply to AC power (100-240 Vac, 47-63 Hz, 1.6 A). The use of an appropriate surge protector is highly recommended. However, unless the entire system can be powered from an uninterruptible power supply (UPS), including the sample pump, this electronics power supply should not be connected to a UPS. This will allow the system to initiate an automatic restart if power is temporarily interrupted.
5) For newer units equipped with a TGAHEAT temperature controller, set the temperature by inserting a small
screwdriver into the Temperature Setting hole in the TGAHEAT module in the analyzer electronics. Rotate the screw to the desired temperature (10 to 50 °C). Connect its power supply to AC power (85-132 Vac, 3.2 A, or 170­264 Vac, 1.8 A, at 47-63 Hz). The use of an appropriate surge protector and a UPS is highly recommended, to help the automatic restart sequence find the correct absorption line when power is restored.
6) For isotope ratio applications, the short sample cell and the air gap between the dewar and lens and the short
sample cell should be purged to prevent absorption by ambient air, as discussed in section 4.1.4.
More details on configuring the TGA100 to measure a specific trace gas can be found in section 4.1.
2.2 TGA100 PC Installation
The TGA100 includes a standard desktop personal computer (PC) to provide the user interface; controlling the analyzer, and calculating, displaying, and storing data in real time. The TGA PC must be protected from the weather. The TGA PC may be located up to 1650 ft. (500 m) from the TGA100 analyzer, determined by the length of the fiber optic interconnect cable. To install the TGA PC:
1) Connect the monitor, keyboard, and mouse (if applicable) to the TGA100 PC.
2) Connect the PC and monitor to AC power. The PC and monitor should operate with any AC power (115/230 Vac,
50/60 Hz). However, if this is an initial installation, check the voltage selector on the PC for proper setting (115/230 Vac). The use of an appropriate surge protector and uninterruptible power supply (UPS) is highly recommended for the PC. The monitor should be powered with a surge suppressor only.
3) Use the fiber optic cable (CSI PN 7737) to connect the analyzer to the link adapter card in the TGA PC.
4) Connect the link adapter card in the TGA PC to the transputer card in the PC. There are two versions of the
transputer card, with a different style connector and cable.
a) For older TGA100s, connect the 18-inch cable with one 8-pin mini-din connector and one RJ45 telephone-
type connector (CSI PN 10699) between the link adapter board and the third (center) connector on the PC transputer board. Connect the cable with two 8-pin mini-din connectors (CSI PN 7917) between the two adjacent connectors on the transputer which are farthest from the PC’s mother board, as shown in Figure 2-2.
24
Single Stand-Alone System
Transputer Board
TLINK
Link Adapter
OUT
IN
Figure 2-2. Link Adapter Cable Connections
Fiber optic out to TGA
b) Newer TGAs have a transputer board with a single “D” connector, and a single cable assembly to make this
connection.
5) Connect the 7996 I/O terminal board (if needed) to the optional 7996 I/O board in the TGA PC.
2.3 Routine Operation
Once the TGA100 has been set up, it should be checked periodically to verify proper operation, download data files, and fill the laser dewar with liquid nitrogen, if necessary. This section gives suggestions for routine operating procedures.

2.3.1 Startup Procedure

This section describes the routine startup procedure for the TGA100. It assumes the TGA100 has been operational and is being restarted after a routine shutdown. This section is not intended as a full explanation of the operation of the TGA100; it is a brief checklist, with cross references to other sections of the manual which provide more detail.
1) Verify the laser dewar vacuum integrity. See section 8.1.
2) Cool the laser dewar. See section 8.1. Do not turn the laser on until it is cold. To run the TGA program with the
laser warm, disable the laser at the main menu before proceeding to the real time screen.
3) If the TGA100 is equipped with the optional liquid nitrogen-cooled detectors (used for long wavelength operation),
cool the detectors with liquid nitrogen. If the TGA100 is equipped with the standard thermoelectric-cooled detectors, they will be cooled automatically.
4) Start the sample vacuum pump.
5) Turn on the reference gas. A flow rate of approximately 10 ml/min is recommended.
6) Turn on the air gap purge gas, if required (isotope ratio measurements). A flow rate of approximately 10 ml/min is
recommended.
7) Turn on calibration gas supplies, if applicable.
8) Power up the TGA analyzer.
9) Power up the TGA PC, start the TGA program, and start real time operation (see section 3.2).
10) Verify the TGA pressure is consistent with the previous operation of the TGA. The sample pump capacity and the
total flow at the pump determine the pressure. Therefore, if the pressure has changed, it may indicate a problem in the plumbing.
11) Wait for the laser temperature to stabilize.
12) Verify the correct absorption line is being scanned. See section 0.
13) Initiate the line lock algorithm to bring the absorption line to the center of the spectral scan.
14) For dual ramp applications, start the ramp B line lock.
15) Verify the detector signals are consistent with previous operation of the TGA. If they have changed, check the
operational parameters (see section 4.4.)
16) Verify the reference transmittance at the center of the absorption line is consistent with previous operation of the
TGA. This transmittance is dependent on which absorption line is selected, the concentration in the reference cell, the pressure in the reference cell, and the laser performance. A significant change indicates a problem.
17) Check the concentration standard deviation to verify proper performance.
The TGA100 is now fully functional. Other features such as Site Means or Gradient Mode, communication with other devices, or data collection may now be started.

2.3.2 Shutdown Procedure

This section describes the routine shutdown procedure for the TGA100. It assumes the TGA100 is operating in the Real Time mode.
1) If data collection is on, turn it off.
2) If Site Means or Gradient mode is on, turn it off.
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3) Exit the Real Time display mode.
4) Exit the TGA program.
5) Shut off power to the TGA PC and monitor.
6) Shut off the TGA sample pump.
7) Shut off power to the TGA enclosure.
8) Shut off the reference gas supply.
9) Shut off the air gap purge supply, if applicable.
10) Shut off calibration gas supplies, if applicable.
If the TGA100 is not to be operated for an extended period, allow the laser to warm up. If the laser is to be operated again in the near future, it is recommended to keep the laser cold to avoid temperature cycling the laser.

2.3.3 System Checks

The TGA100 is often used for long term continuous measurements. It is necessary to periodically check the status of the system, perform routine maintenance, and transfer data for offline analysis.
1) Look for a message printed in red above graph 1 indicating the system has restarted. If it has restarted, it is
important to verify it is on the correct absorption line.
2) Verify concentration data collection and site means or gradient mode are ON (if used).
3) Verify the line lock is ON. If the TGA100 is in dual ramp mode, also verify the Ramp B line lock is ON.
4) Note the DC current (it is recommended that this be recorded in a log book). Compare it to the expected value to
verify the laser is still operating on the desired absorption line. If the TGA100 is in dual ramp mode, also note the Ramp B offset.
5) Verify that the concentration and concentration noise are as expected. If the TGA100 is in dual ramp mode, also
verify the Ramp B concentration and noise.
6) Note the sample pressure (it is recommended that this be recorded in a log book). Compare this to the previous
values. The pressure will decrease over time as the sample intake filter(s) becomes plugged.
7) Note the laser heater voltage (it is recommended that this be recorded in a log book). Compare this to the previous
values. The vacuum inside the laser dewar will gradually degrade. This degradation reduces the thermal isolation between the outer wall of the laser dewar and the laser itself. Over time, as more heat is transferred to the laser by the degraded vacuum, less heat is needed to maintain the laser at the set temperature, and the laser heater voltage will gradually decrease. Therefore, monitoring the laser heater voltage may give an indication of when it is time to evacuate the dewar. This is especially important for cryocooler systems and for lasers that must operate at very cold temperatures.
8) Exit the real time screen and stop the TGA program.
9) Download data. The details will vary from one system to another. The data can then be transferred by copying to
CD ROM, Zip disk, etc. Check the files to verify the expected files are present.
10) As soon as the data are downloaded, restart the TGA program and go to the real time screen. This will let the laser
and detector temperatures stabilize as the next steps are completed.
11) If needed, fill the laser dewar with liquid nitrogen. If the TGA is equipped with liquid nitrogen cooled detectors,
fill these as needed.
12) Check the reference gas tank and regulator pressure. Check other tanks (air gap purge, calibration, etc.) as needed.
13) If a change in the sample pressure indicates the sample intake filter(s) must be changed, shut off the sample
vacuum pump. Wait for the pressure to reach ambient, and then replace the filter element(s). Restart the sample vacuum pump.
14) Restart the TGA (see section 2.3.1).
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3 TGA SOFTWARE
3.1 General
The TGA software runs on the TGA PC. It provides the user interface to the TGA100, allowing the user to view the operation of the TGA, set parameters, and collect data. The TGA program actually is a set of three programs that run concurrently on three computers, communicating in real time. The first computer is the TGA PC itself. It runs the user interface and data storage functions of the TGA software. The second computer is the 9030 CPU module mounted in the TGA electronics chassis in the TGA enclosure. This computer controls the detector temperatures, the laser temperature and current, performs the measurements, and sends the data to the third computer, which is the transputer board mounted in the TGA PC. This third computer acts as an interface between the other two, and performs most of the calculations required to compute the concentration. When two or more TGA100s are linked together in the master/slave configuration, the transputer board also provides the communication link between them.
Normally it is not important for the user to be aware of the three computers and the roles they play. It is sufficient to know that the TGA program runs on the TGA PC, the transputer board must be installed in the PC, and the transputer board must be connected to the TGA enclosure through the link adapter and the fiber optic cable. However this information may be useful in troubleshooting problems.
The following sections discuss the details of the TGA software.
3.2 Startup
The TGA program is a DOS mode program. Although it may be run under the Windows operating system, it will run more reliably when the TGA PC is started in DOS mode.
The executable file is TGA.EXE, normally installed in the C:\TGA directory. The program is started by setting the default path to C:\TGA and entering the command <TGA>. The TGA program starts at the main menu.
3.3 Main Menu
When the TGA program is started, the main menu is displayed as shown below:
Figure 3-1. Main Menu
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The functions available at the main menu are described below.
R) Real Time TGA Program
Turns the TGA on and displays the real time screen. This is the normal operating mode. See section 3.4 for
additional information.
T) TGA on/off
Toggles the TGA on or off. When the TGA is on, all current and temperature controls are active and
concentration calculations are being made, but the real time screen is not displayed, and no data are saved to the hard disk.
L) Laser on/off
Toggles the laser on or off. The laser must be on during normal operation. The laser may be disabled to
operate the TGA100 without driving the laser. For example, the laser temperature may be monitored during the initial cool down by disabling the laser at the main menu and then entering the real time screen.
P) Parameter Change Menu
Displays submenus for changing parameters. See section 3.5 for additional information.
M) Laser Mapping Menu
Displays the mapping submenu to be used to characterize a laser. See section 4.3 for additional information.
X) Exit
Exit TGA program.
3.4 Real Time Screen
The Real Time Screen is entered by pressing “R” at the main menu (see section 0.) This is the normal operating mode for the TGA100. Concentration data can be displayed or saved only while in the real time mode.
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3.4.1 Screen Layout

The real time graphics screen is presented in . In the upper left corner is a box which displays the TGA software version, the laser and detector temperatures, and the time. Beneath the time and temperature display is a blank area used for information and error message display. The rest of the top of the screen has five menu columns: run mode, dynamic parameters, detector video, special function enable/disable, and graph selections.
Figure 3-2
Figure 3-2. Example Real Time Screen
In the middle of the screen are graph 1 and graph 2, used to display certain user-selectable variables. The horizontal time step is 0.1 sec and the horizontal width is 280 pixels or 28 seconds. The title bar at the top of each window shows the variable name, the floating point value and its standard deviation, and the units. The maximum and minimum display limits are shown in the upper right and lower right corners.
Graph 3 is located at the bottom-center of the screen, and is used to display user-selected variables. The graph 3 window is 150 pixels wide or 15 seconds. Graph 3 also has the variable name, value, standard deviation, and display limits noted on the graph.
At the bottom left corner of the screen are two high speed graphic windows that show the raw reference (REF) detector signal and the raw sample (SMP) detector signal, scaled to match the analog-to-digital converter (ADC) input range.
At the bottom right corner of the screen are two more high speed graphic windows that display processed reference and sample signals. The user may select the type of data to display in these windows using the Detector Video menu or the Quick Keys. The number displayed at the top of these windows is either the transmittance or the absorbance of the center of the spectral scan, depending on the display mode selected. All four of the high-speed graphic windows have three vertical dashed lines. These lines show the center of the spectral scan and the range of data actually used to calculate concentration.
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3.4.2 Navigating and Editing

The <left/right arrow> keys are used to cycle through the following menus: RUN MODE, PARAMETER, DET VID, FUNCTION, GRAPH 1, GRAPH 2, GRAPH 3, DETECTORS, Graph 1 display scale, and Graph 2 display scale. The heading for the current menu is highlighted. The active option within each menu is also highlighted. The <up/down arrow> keys are used to select a specific option (marked with an asterisk “*”) within the selected menu and the <Enter> key is used to activate the option. To adjust the value of a numeric field (dynamic parameter or graph display limit), use the <Home End> keys for coarse adjustments, <Page Up Page Down> keys for normal adjustments, the <+-> keys for fine adjustments, and the </ *> keys for very fine adjustments. Number pad and keyboard give the same results. Each field is described below.

3.4.3 Run Mode

The first menu in the Real Time screen controls the run mode. The options are Quit, Run, or Run/Edit.
Upon entering the Real Time Screen, the run mode is Run/Edit which enables the display and parameters to be edited using either cursor motion or the Quick keys.
Once operating conditions have been established, the Run mode may be selected to disable the Quick keys and editing capability. This may be useful to avoid problems caused by pressing a key inadvertently. In Run mode, the user may adjust the display, but can not adjust any of the dynamic parameters are operating functions.
Quit stops real time operation and returns program control to the main menu. The hardware continues to control and monitor temperatures but any open data storage files are closed. The <escape> key has the same effect as selecting Quit.
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