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Campbell Scientific TGA200A TGA Series Trace Gas Analzyers - Page 145

TGA100 and TGA100A, Multimode, power, Multimode power, Settings > Laser > Other, Laser Settings

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Appendix C. Optimizing Laser Parameters NOTE NOTE other frequencies will generally not be absorbed. The measured transmittance at the center of the absorption line gives an estimate of the laser multimode power. Two different methods are used depending on the TGA model TGA100 and TGA100A TGA100s and TGA100As have a long sample cell and a short reference cell. The laser's multimode power can be estimated by temporarily putting reference gas in the long sample cell. This increases the path length by a factor of almost 34. This test is best performed in conditions in which there is not an excessive amount of absorption as this can lead to two possible problems. First, the absorption lines become broader, and absorption in the tails of the absorption line can reduce the response at the edges of the spectral scan that are assumed to be 100% transmittance. This will give an error in the estimate of multimode power, especially if there is another absorption line nearby. Second, too much absorption will increase the chances of absorbing the multimode power in some other absorption lines of the gas. The correct absorption can usually be achieved by adjusting the pressure in the sample cell. To begin, go to the Settings > Laser > Other window and set the Multimode power % to zero. Then note the reference transmittance in the Laser Settings window. The transmittance measurement is affected by detector nonlinearity (see Appendix D.4, Detector Linearity Coefficients). The reference detector is more linear because it has a smaller signal. Therefore this measurement should be based on the reference detector, not the sample detector. To achieve the optimum amount of absorption, first note the reference transmittance with reference gas in the reference cell only (the normal configuration). Normally, the reference gas concentration is chosen to give approximately 50% absorption. For this test, however, it is best to have between 70% and 80% absorption. Usually this can be accomplished by reducing the sample flow to reduce the pressure in the analyzer. When the proper absorption is achieved, record the sample cell pressure. It is acceptable for the transmittance to be less than 70%, but it must NOT be greater than 80%. To configure the instrument for the multimode test, turn off the sample pump, swap the reference gas and sample connections, and turn the pump back on. This will put the reference gas in the long sample cell and the air sample in the short reference cell. The total flow to the sample pump should be the same as before, so the pressure should also be the same. Verify the pressure is within 10% of the previous pressure. Adjust the laser modulation current as needed - the increased absorption may make the line wider. Record the reference transmittance, shown in the Laser Settings window. This is the estimate of the laser's multimode power. Enter this value as the Multimode power (%) parameter in the Settings > Laser > Other window. Verify the reference transmittance is near zero. C-13

Section	Page
Revision and Copyright Information	1
Limited Warranty	3
Assistance	4
Precautions	5
Table of Contents	7
1. Introduction	15
2. Cautionary Statements	16
3. Initial Inspection	17
4. Overview	17
4.1 System Components	20
4.1.1 Standard Components	21
4.1.1.1 TGA Power Module	21
4.1.1.2 TGA Accessory & Tool Kit	22
4.1.1.3 TGA Test Intake	22
4.1.1.4 TGA Leak Check Nozzle	22
4.1.1.5 TGA SDM Cable	23
4.1.1.6 Plastic Tubing	23
4.1.1.7 CAT5 Ethernet Crossover Cable	23
4.1.1.8 Serial Data Cable	24
4.1.1.9 TGA TEC Support Software and Operating System	24
4.1.2 Optional Components	25
4.1.2.1 Laser	25
4.1.2.2 AC Mains Power Cord	25
4.1.2.3 Power Module Mounting Brackets	26
4.1.3 Common Accessories	26
4.1.3.1 TGA Reference Gas Connection	26
4.1.3.2 TGA Insulated Enclosure Cover	27
4.1.4 Other Accessories	28
4.1.4.1 TGA Air Sample Intake	28
4.1.4.2 TGA Heated Intake Filter & Orifice	28
4.1.4.3 TGA High-Flow Filter Holder	28
4.1.4.4 Sample Vacuum Pump	29
4.1.4.5 Bypass Vacuum Pump	31
4.1.4.6 Sample Air Dryer	32
4.1.4.7 TGA Rotameter	35
4.1.5 Support Software	36
4.1.6 Replacement Parts	36
4.1.6.1 TGA Heated Intake Filter	36
4.1.6.2 Filter Element	36
4.1.6.3 TGA Filter Elements, 47mm (Qty 100)	37
4.2 Theory of Operation	37
4.2.1 Optical System	37
4.2.2 Laser	39
4.2.3 Dewars	39
4.2.4 Detectors	39
4.2.5 Laser Scan Sequence	40
4.2.6 Concentration Calculation	41
5. Specifications	42
5.1 Measurement Specifications	42
5.2 Physical Specifications	43
5.3 Power Requirements	43
6. Installation	44
6.1 Analyzer Installation	45
6.1.1 Plumbing Connections	47
6.1.2 Data Output Connections	49
6.1.3 Power	51
6.2 TGA Software Installation	53
6.2.1 Installation of PC Software	53
6.2.2 Updating TGA Operating System	54
6.2.3 Configure Ethernet Connection	56
6.2.4 Set TGA Serial Number and Identification String	59
6.2.5 Run the PC Software	60
6.3 Detailed Setup Instructions	60
7. Operation	60
7.1 Routine Operation	60
7.1.1 Startup Procedure	60
7.1.2 Routine System Checks	61
7.1.3 Shutdown Procedure	62
7.2 Software User Interface	63
7.2.1 Connect Window	63
7.2.2 Status Window	65
7.2.3 Settings Window	66
7.2.3.1 Laser	67
7.2.3.2 Detectors	73
7.2.3.3 Calculations	75
7.2.3.4 Other	80
7.2.4 Laser Window	84
7.2.4.1 View Less/View More	85
7.2.4.2 Tabbed/Expand	86
7.2.4.3 Display Mode	87
7.2.4.4 Colors	95
7.2.5 Find	95
7.2.6 Graph	98
7.2.7 Data	101
7.2.8 Files	102
7.3 Data Output	104
7.3.1 SDM Output	104
7.3.1.1 Syntax	105
7.3.1.2 Remarks	105
7.3.2 TGA Output to PC	108
7.3.3 TGA Analog Outputs	108
8. Troubleshooting and Maintenance	108
8.1 Lasers and Detectors	108
8.2 Reference Gas	109
8.3 Filtration and Sample Cell Cleaning	109
8.4 Sample Pumps	109
Appendix A. Configuring TGAs for Specific Gas Species	111
A.1 Laser Selection	111
A.1.1 LN2-cooled lasers	111
A.1.2 TE-cooled Lasers	111
A.1.3 Dewar Cables	112
A.1.4 Changing Lasers	112
A.2 Reference Gas	114
A.3 Detectors	116
A.4 Finding the Absorption Line	116
A.5 Air Gap Purge	117
Appendix B. Optical Alignment	119
B.1 Optical Alignment of TGA100 and TGA100A	119
B.1.1 Initial Alignment	122
B.1.2 Horizontal and Vertical Alignment	123
B.1.3 Focus Adjustment	124
B.1.4 Reference Detector Coalignment	125
B.2 Optical Alignment of TGA200 and TGA200A	125
B.2.1 Configure the TGA PC Software	127
B.2.2 Initial Alignment	127
B.2.3 Horizontal and Vertical Alignment	130
B.2.4 Focus Adjustment	131
Appendix C. Optimizing Laser Parameters	133
C.1 Laser Temperature	133
C.2 Zero Current	137
C.3 High Current	139
C.3.1 High Current Count	142
C.4 Omitted Data Count	143
C.5 Modulation Current	143
C.6 Laser Maximum Temperature and Laser Maximum Current	144
C.7 Laser Multimode Correction	144
Appendix D. Optimizing Detector Parameters	147
D.1 Detector Gain and Offset	147
D.2 Detector Preamp Gain	147
D.3 Detector Temperature	147
D.4 Detector Linearity Coefficients	148
Appendix E. Calibration	151
Appendix F. TGA Frequency Response	153
F.1 Measurement Rate	153
F.2 Sample Rate	153
F.3 Digital Filters	154
F.4 Synchronicity	156
F.5 Sample Cell Residence Time	157
Appendix G. Using Swagelok® Fittings	159
G.1 General Notes	159
G.2 Assembly	159
G.3 Common Replacement Parts	160
Appendix H. Upgrading Early Generation TGAs to TE-cooled Laser	163
H.1 TGA200	163
H.1.1 Basic Upgrade	163
H.1.2 Detectors	166
H.1.3 Power Module	166
H.1.4 Purge Boot	166
H.2 TGA100A	166
H.2.1 Basic Upgrade	166
H.2.2 Detectors	167
H.2.3 Holes in Enclosure for Cryocooler Refrigerant Tubes	167
H.2.4 Temperature Control Upgrade	167
H.2.5 Power Module	168
H.2.6 Purge Boot	168
H.3 TGA100	168
H.3.1 Basic Upgrade	168
H.3.2 CPU Module	168
H.3.3 Input and Output Modules	168
H.3.4 Detectors and Detector Cables	169
H.3.5 Temperature Controller	171
Appendix I. Install Temperature Control Upgrade	173
I.1 Install Thermistor Probes	173
I.2 Connect the Control Cable	175
I.3 Enter Control Parameters	176
I.4 Testing	176
I.1 Operation	177

Match case Limit results 1 per page

Appendix C.

Optimizing Laser Parameters

other frequencies will generally not be absorbed.

The measured transmittance

at the center of the absorption line gives an estimate of the laser multimode

power. Two different methods are used depending on the TGA model

TGA100 and TGA100A

TGA100s and TGA100As have a long sample cell and a short reference cell.

The laser’s multimode power can be estimated by temporarily putting reference

gas in the long sample cell.

This increases the path length by a factor of almost

34.

This test is best performed in conditions in which there is not an excessive

amount of absorption as this can lead to two possible problems.

First, the absorption lines become broader, and absorption in the tails of the

absorption line can reduce the response at the edges of the spectral scan that are

assumed to be 100% transmittance.

This will give an error in the estimate of

multimode power, especially if there is another absorption line nearby.

Second, too much absorption will increase the chances of absorbing the

multimode power in some other absorption lines of the gas.

The correct

absorption can usually be achieved by adjusting the pressure in the sample cell.

To begin, go to the

Settings > Laser > Other

window and set the

Multimode

power %

to zero. Then note the reference transmittance in the

Laser Settings

window.

The

transmittance

measurement

affected

detector

nonlinearity (see Appendix D.4,

Detector Linearity Coefficients

The reference detector is more linear because it has a smaller

signal. Therefore this measurement should be based on the

reference detector, not the sample detector.

To achieve the optimum amount of absorption, first note the reference

transmittance with reference gas in the reference cell only (the normal

configuration). Normally, the reference gas concentration is chosen to give

approximately 50% absorption. For this test, however, it is best to have

between 70% and 80% absorption. Usually this can be accomplished by

reducing the sample flow to reduce the pressure in the analyzer. When the

proper absorption is achieved, record the sample cell pressure.

It is acceptable for the transmittance to be less than 70%, but it

must NOT be greater than 80%.

To configure the instrument for the multimode test, turn off the sample pump,

swap the reference gas and sample connections, and turn the pump back on.

This will put the reference gas in the long sample cell and the air sample in the

short reference cell.

The total flow to the sample pump should be the same as

before, so the pressure should also be the same.

Verify the pressure is within

10% of the previous pressure.

Adjust the laser modulation current as needed – the increased absorption may

make the line wider.

Record the reference transmittance, shown in the

Laser

Settings

window.

This is the estimate of the laser's multimode power. Enter

this value as the

Multimode power (%)

parameter in the

Settings > Laser >

Other

window.

Verify the reference transmittance is near zero.

NOTE

C-13