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Campbell Scientific TGA200A TGA Series Trace Gas Analzyers - Page 147

Appendix D. Optimizing Detector Parameters, D.1 Detector Gain and Offset, D.2 Detector Preamp Gain

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Appendix D. Optimizing Detector Parameters Set the detector parameters after the laser parameters are adjusted. D.1 Detector Gain and Offset The detector signals are processed in the TGA electronics, which include an amplifier with programmable gain and offset in the input module, and a second programmable-gain amplifier in the analog module. The detector gains and offsets are normally controlled automatically by the TGA software. To enable this automatic control, click the Auto gain/offset box on the Settings > Detectors > Preamp window. To set the offsets and gains manually, adjust one of the values to disable the automatic function. The detector gains and offsets should usually be controlled automatically. However there are two exceptions. First, automatic control should be disabled while performing some of the setup steps, such as optical alignment. Second, the automatic gain algorithm will not increase the sample gain beyond gain 7. Therefore, if the detector signals are extremely weak, it may be necessary to set the detector gains and offsets manually. D.2 Detector Preamp Gain The detector electronics have a fixed gain in the first preamplifier stage. Early TGAs used a gain of 200, but this was changed to 45 for TGA200s and TGA200As. This reduced gain allows the detector signals to be larger without saturating the input range. This is an advantage for higher-power lasers, and for LN2-cooled detectors used for longer wavelengths. Some early input modules have been modified to use a gain of 45 in the preamp. These instruments are identified by a label on the printed circuit board: Gain 45. Input modules upgraded for use with TE-cooled lasers have a gain of 45. These modules have a blue label on the top that designates them for use with TE-cooled lasers (see Appendix H.3.1, Basic Upgrade). The preamp gain (either 45 or 200) must be entered in the parameters at the Settings > Detectors > Preamp window. If it is unclear which gain is the correct one for a specific input module, or if an input module upgrade is desired, contact Campbell Scientific. D.3 Detector Temperature Most TGAs are equipped with TE-cooled detectors, but some are equipped with LN2-cooled detectors to work with longer-wavelength lasers. LN2-cooled detectors have no temperature measurement or control. They are designed to operate near LN2's boiling point, 77 K. TE-cooled detectors include a thermistor to measure the detector's temperature. The TGA measures this temperature and adjusts the TE-cooled current to cool the detector to the setpoint. Generally, a lower detector temperature will increase the detector signal and decrease the concentration noise. However, some lasers emit enough power to saturate the detectors if they are cooled to D-1

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 D. Optimizing Detector

Parameters

Set the detector parameters after the laser parameters are adjusted.

D.1 Detector Gain and Offset

The detector signals are processed in the TGA electronics, which include an

amplifier with programmable gain and offset in the input module, and a second

programmable-gain amplifier in the analog module.

The detector gains and

offsets are normally controlled automatically by the TGA software.

To enable

this automatic control, click the

Auto gain/offset

box on the

Settings >

Detectors > Preamp

window.

To set the offsets and gains manually, adjust

one of the values to disable the automatic function.

The detector gains and offsets should usually be controlled automatically.

However there are two exceptions.

First, automatic control should be disabled

while performing some of the setup steps, such as optical alignment.

Second,

the automatic gain algorithm will not increase the sample gain beyond gain 7.

Therefore, if the detector signals are extremely weak, it may be necessary to set

the detector gains and offsets manually.

D.2 Detector Preamp Gain

The detector electronics have a fixed gain in the first preamplifier stage. Early

TGAs used a gain of 200, but this was changed to 45 for TGA200s and

TGA200As. This reduced gain allows the detector signals to be larger without

saturating the input range. This is an advantage for higher-power lasers, and

for LN

-cooled detectors used for longer wavelengths. Some early input

modules have been modified to use a gain of 45 in the preamp. These

instruments are identified by a label on the printed circuit board:

Gain 45

Input modules upgraded for use with TE-cooled lasers have a gain of 45.

These modules have a blue label on the top that designates them for use with

TE-cooled lasers (see Appendix H.3.1,

Basic Upgrade

The preamp gain (either 45 or 200) must be entered in the parameters at the

Settings > Detectors > Preamp

window. If it is unclear which gain is the

correct one for a specific input module, or if an input module upgrade is

desired, contact Campbell Scientific.

D.3 Detector Temperature

Most TGAs are equipped with TE-cooled detectors, but some are equipped

with LN

-cooled detectors to work with longer-wavelength lasers. LN

-cooled

detectors have no temperature measurement or control. They are designed to

operate near LN

’s boiling point, 77 K.

TE-cooled detectors include a thermistor to measure the detector’s temperature.

The TGA measures this temperature and adjusts the TE-cooled current to cool

the detector to the setpoint. Generally, a lower detector temperature will

increase the detector signal and decrease the concentration noise. However,

some lasers emit enough power to saturate the detectors if they are cooled to

D-1