Teledyne GC-Pro-TCD User Manual
INSTRUCTION, OPERATING AND
MAINTENANCE MANUAL FOR
GC-PRO TCD
P/N M89443
DATE 4/05/13
Toxic and/or flammable gases or liquids may be present in this monitoring system.
Personal protective equipment may be required when servicing this instrument.
Hazardous voltages exist on certain components internally which may persist for
a time even after the power is turned off and disconnected.
Only authorized personnel should conduct maintenance and/or servicing. Before
conducting any maintenance or servicing, consult with authorized
supervisor/manager.
Teledyne Analytical Instruments
DANGER
GC-Pro TCD
Copyright © 2013 Teledyne Analytical Instruments
All Rights Reserved. No part of this manual may be reproduced, transmitted, transcribed,
stored in a retrieval system, or translated into any other language or computer language in
whole or in part, in any form or by any means, whether it be electronic, mechanical,
magnetic, optical, manual, or otherwise, without the prior written consent of Teledyne
Analytical Instruments, 16830 Chestnut Street, City of Industry, CA 91748.
Warranty
This equipment is sold subject to the mutual agreement that it is warranted by us free from
defects of material and of construction, and that our liability shall be limited to replacing or
repairing at our factory (without charge, except for transportation), or at customer plant at
our option, any material or construction in which defects become apparent within one year
from the date of shipment, except in cases where quotations or acknowledgements provide
for a shorter period. Components manufactured by others bear the warranty of their
manufacturer. This warranty does not cover defects caused by wear, accident, misuse,
neglect or repairs other than those performed by Teledyne or an authorized service center.
We assume no liability for direct or indirect damages of any kind and the purchaser by the
acceptance of the equipment will assume all liability for any damage which may result from
its use or misuse.
We reserve the right to employ any suitable material in the manufacture of our apparatus,
and to make any alterations in the dimensions, shape or weight of any parts, in so far as
such alterations do not adversely affect our warranty.
Important Notice
This instrument provides measurement readings to its use r, an d serves as a tool b y whic h
valuable data can be gathered. The information provided by the instrument may assist the user
in eliminating potential hazards caused by his process; however, it is essential that all
personnel involved in the use of the instrument or its interface be properly trained in the
process being measured, as well as all instrumentation related to it.
The safety of personnel is ultimately the responsibility of those who control process
conditions. While this instrument may be able to provide early warning of imminent
danger, it has no control over process conditions, and it can be misused. In particular, any
alarm or control systems installed must be tested and understood, both as to how they
operate and as to how they can be defeated. Any safeguards required such as locks, labels,
or redundancy, must be provided by the user or specifically requested of Teledyne at the
time the order is placed.
Therefore, the purchaser must be aware of the hazardous process conditions. The purchaser
is responsible for the training of personnel, for providing hazard warning methods and
instrumentation per the appropriate standards, and for ensuring that hazard warning devices
and instrumentation are maintained and operated properly.
Teledyne Analytical Instruments, the manufacturer of this instrument, cannot accept
responsibility for conditions beyond its knowledge and control. No statement expressed or
implied by this document or any information disseminated by the manufacturer or its
agents, is to be construed as a warranty of adequate safety control under the user’s process
conditions.
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Safety Messages
Your safety and the safety of others are very important. We have
provided many important safety messages in this manual. Please read
these messages carefully.
A safety message alerts you to potential hazards that could hurt you
or others. Each safety message is associated with a safety alert symbol.
These symbols are found in the manual and inside the instrument. The
definition of these symbols is described below:
GENERAL WARNING/CAUTION: Refer to the
instructions for details on the specific danger. These
cautions warn of specific procedures which if not
followed could cause bodily Injury and/or damage the
instrument.
No
Symbol
CAUTION: HOT SURFACE WARNING: This warning is
specific to heated components within the instrument.
Failure to heed the warning could result in serious burns
to skin and underlying tissue.
WARNING: ELECTRICAL SHOCK HAZARD: Dangerous
voltages appear within this instrument. This warning is
specific to an electrical hazard existing at or nearby the
component or procedure under discussion. Failure to heed
this warning could result in injury and/or death from
electrocution.
Technician Symbol: All operations marked with this
symbol are to be performed by qualified maintenance
personnel only.
NOTE: Additional information and comments regarding
a specific component or procedure are highlighted in the
form of a note.
STAND-BY: This symbol indicates that the instrument is
on Stand-by but circuits are active.
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CAUTION: THE ANALYZER SHOULD ONLY BE USED FOR THE
PURPOSE AND IN THE MANNER DESCRIBED IN
THIS MANUAL.
IF YOU USE THE ANALYZER IN A MANNER OTHER
THAN THAT FOR WHICH IT WAS INTENDED,
UNPREDICTABLE BEHAVIOR COULD RESULT
POSSIBLY ACCOMPANIED WITH HAZARDOUS
CONSEQUENCES.
This manual provides information designed to guide you through the
installation, calibration and operation of your new analyzer. Please read
this manual and keep it available.
Occasionally, some instruments are customized for a particular
application or features and/or options added per customer requests.
Please check the front of this manual for any additional information in
the form of an Addendum which discusses specific information,
procedures, cautions and warnings that may be specific to your
instrument.
Manuals do get misplaced. Additional manuals can be obtained from
Teledyne at the address given in the Appendix. Some of our manuals are
available in electronic form via the internet. Please visit our website at:
www.teledyne-ai.com.
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Additional Safety Information
DANGER
COMBUSTIBLE GAS USAGE
This is a general purpose instrument designed for use in a
non-hazardous area. It is the customer's responsibility to
ensure safety especially when combustible gases are being
analyzed since the potential of gas leaks always exist.
WARNING
The customer should ensure that the principles of operating
of this equipment are well understood by the user. Misuse of
this product in any manner, tampering with its components,
or unauthorized substitution of any component may
adversely affect the safety of this instrument.
Since the use of this instrument is beyond the control of
Teledyne, no responsibility by Teledyne, its affiliates, and
agents for damage or injury from misuse or neglect of this
equipment is implied or assumed.
WARNING: If toxic or flammable gases are used, always purge
the entire system before performing any
maintenance and always leak check the system after
removing any tubing or fittings on the sample
system. See the procedures for purging and leak
checking this instrument on the following pages.
If toxic gases or other hazardous materials are
introduced into the sample system, the same
precautions regarding leak checking and purging
apply to the sample lines and sample supply or
delivery lines.
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WARNING: ELECTRICAL SHOCK HAZARD.
ONLY AUTHORIZED AND SUITABLY TRAINED
PERSONNEL SHOULD PERFORM WORK INSIDE OF
THE INSTRUMENT. COMPONENTS WITHIN THE
COVER, INSIDE THE ISOTHERMAL CHAMBER
(SAMPLE SYSTEM), AND ON PC BOARDS MAY
CONTAIN DANGEROUSLY HIGH VOLTAGE
SUFFICIENT TO CAUSE SERIOUS INJURY OR
DEATH.
There are the following three types of inaccessible
shock hazards within the Analyzer:
1. Line voltages and line related voltages such as
115 VAC which exists within the 230 VAC
versions as well. These voltages stop when the
Analyzer is turned off and the mains (line) cord is
removed from the instrument.
2. External hazardous voltages which may be
connected to the Analyzer alarm relay
connections.
WARNING: THIS INSTRUMENT IS DESIGNED TO BE OPERATED
IN A NONHAZARDOUS AREA. DEPENDING ON THE
APPLICATION, TOXIC GASES OR
FLAMMABLE/EXPLOSIVE GASES MAY BE
PRESENT. IT IS THEREFORE, THE CUSTOMER'S
RESPONSIBILITY TO ENSURE THAT PROPER
TRAINING AND UNDERSTANDING OF THE
PRINCIPLES OF OPERATION OF THIS EQUIPMENT
ARE UNDERSTOOD BY THE USER. SINCE THE USE
OF THIS INSTRUMENT IS BEYOND THE CONTROL
OF TELEDYNE, NO RESPONSIBILITY BY TELEDYNE,
ITS AFFILIATES AND AGENTS FOR DAMAGE OR
INJURY RESULTING FROM MISUSE OR NEGLECT
OF THIS INSTRUMENT IS IMPLIED OR ASSUMED.
MISUSE OF THIS PRODUCT IN ANY MANNER,
TAMPERING WITH ITS COMPONENTS OR
UNAUTHORIZED SUBSTITUTION OF ANY
COMPONENT MAY ADVERSELY AFFECT THE
SAFETY OF THIS INSTRUMENT.
CAUTION: WHEN OPERATING THIS INSTRUMENT, ALL
COVERS SECURELY FASTENED. THE GAUGES
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MUST BE IN PROPER WORKING ORDER. DO NOT
OVERPRESSURIZE THE SYSTEM.
READ THIS MANUAL BEFORE OPERATING THE
INSTRUMENT AND ADHERE TO ALL WARNINGS
INCLUDED IN THIS MANUAL.
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Table of Contents
Safety Messages .......................................................................... iii
Additional Safety Information ...................................................... v
List of Figures ............................................................................. xii
List of Tables .............................................................................. xiii
Introduction ................................................................................... 1
1.1 Main Features of the Analyzer 1
1.2 Principle of Operation 3
1.3 Analyzer Description 3
1.4 Applications 7
Operational Theory ....................................................................... 9
2.1 Introduction 9
2.2 Modes of Operation 10
2.3 Analyzer Subsystems 11
2.3.1 Sample System 11
2.3.2 Gas Flow Control System 12
2.3.3 Gas Separation System 14
2.4 Detector Cell 14
Installation ................................................................................... 17
3.1 Unpacking the Analyzer 17
3.2 Mounting the Analyzer 17
3.3 User Connections 18
3.3.1 Electrical Power Connections 18
3.3.2 Electronic Connections 18
3.3.2.1 Primary Input Power 19
3.3.2.2 Fuse Installation 20
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3.3.2.3 50-Pin Equipment Interface Connector 20
3.3.2.4 Analog Output 20
3.3.2.5 Alarm Relays 22
3.3.2.6 Digital Remote Cal Inputs 24
3.3.2.7 ‘Measure Once’ (or one shot measurement)
contacts 25
3.3.2.9 Pin Out Table 25
3.3.2.10 RS-232 Port 28
3.3.3 Gas Connections 29
3.3.3.1 Effluent 31
3.3.3.2 Sensor Vent 31
3.3.3.3 Carrier Gas Connection 31
3.3.4 Sample and Span Gas Connections 31
3.4 Placing the System in Operation 32
Operation ..................................................................................... 33
4.1 Equipment 34
4.2 Preliminary Power-Off Check List 34
4.3 Powering Up the Unit 35
4.4 Activating the Support Gases 38
4.4.1 Carrier Gas 38
4.4.2 Span Gas 38
4.5 Analyzer Operation 38
4.5.1 Default Parameters 39
4.5.2 The HOME Screen 40
4.5.3 The MENU Screen 41
4.5.4 Standby 42
4.5.5 Overlay Chromatogram 44
4.5.6 Timing 46
4.5.6.1 TCD Amplifier Gain 50
4.5.7 Temperature 50
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4.5.7.1 Thermocouple 51
4.5.7.2 Settings 52
4.5.7.3 PID Settings 53
4.5.7.4 Status 54
4.5.8 Group Setup 55
4.5.9 Analog Adjust 58
4.5.10 Calibration 59
4.5.10.1 Span 60
4.5.10.2 Alt Span 62
4.5.10.3 Auto cal 65
4.5.11 Self Test 66
4.5.12 Settings 68
4.5.12.1 Alarms 69
4.5.12.2 Range 72
4.5.12.3 Change Stream 74
4.5.12.4 Time 75
4.5.12.5 Password 76
4.5.12.6 Communication 76
4.5.12.7 Detector 78
4.5.12.8 Set TCD 79
4.5.12.9 Cycle Mode 80
4.5.13 Analysis Mode 80
4.5.13.1 T-Time 81
4.5.13.2 T_Cycle 82
4.5.13.3 Chromatogram 83
4.5.13.4 VS Count 85
4.5.13.5 Cold Boot 85
Maintenance & Troubleshooting ................................................ 89
Appendix ...................................................................................... 91
A.1 Specifications and Initial Settings: 91
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A.2 Recommended Spare Parts List 92
A.3 Drawing List 93
Appendix B .................................................................................. 95
B1. VNC for GC-Pro TCD 95
Appendix C ................................................................................ 101
C1 Addendum and Testing Results 101
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List of Figures
Figure 1-1: GC-Pro TCD Front Panel .............................................. 4
Figure 1-2: GC-Pro TCD Rear Panel .............................................. 5
Figure 1-3: Internal PCB Arrangement ............................................ 6
Figure 1-4: GC-Pro TCD Internal View ............................................ 6
Figure 2-1: Internal Temperature Controllers ................................ 12
Figure 2-2: Typical Piping Diagram Used in the GC-Pro TCD ....... 13
Figure 2-3: Thermal Conductivity Cell Operating Principle ............ 14
Figure 3-1: GC-Pro TCD Rear Panel with Optional Gas Manifold . 19
Figure 3-2: Equipment Interface Connector Pin Arrangement....... 20
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List of Tables
Table 3-1: Analog Output Connections — Middle Connector ........ 21
Table 3-2: Analog Concentration Output—Example ...................... 22
Table 3-3: Alarm Relay Contact Pins — Top Connector ............... 23
Table 3-4: Remote Calibration Connections — Bottom Connector 24
Table 3-5: ‘Measure Once’ Relay Connections ............................. 25
Table 3-6: Pin out of Alarm Relay O/P (Top) 50 pin D-Sub
Connector .................................................................... 26
Table 3-7: Pin out of Analog Signal (Middle) 50 pin D-Sub
Connector .................................................................... 26
Table 3-8: Pin out of Standard (Bottom) 50 pin D-Sub Connectors27
Table 3-9: Commands via RS-232 Input ....................................... 28
Table 3-10: Required RS-232 Options .......................................... 28
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GC-Pro TCD Introduction
Introduction
The GC-Pro TCD Analyzer is a microprocessor controlled digital
instrument incorporating a Thermal Conductivity Detector (TCD)
coupled with a gas separation column and switching valve designed to
measure the quantity of aromatic hydrocarbons present in a positive
pressure sample gas. Up to 8 channels of output are present for
measuring specific analytes in a sample stream. In using a thermal
conductivity detector after gas separation through a column, the range of
analysis is extended to include additional phase separable inert, or other
difficult to analyze gas phase components like N2, H2. etc. that are
present in a positive pressure sample gas.
The GC-Pro TCD Analyzer has multiple channels for measurement
with enhanced versatility and capabilities. Due to its flexibility, it is
vitally important that you refer to Appendix C for the specific factory
setup for your application.
The GC-Pro TCD features a modern user interface with a touch
screen front panel facilitating operation, calibration, data collection and
display. With the Ethernet connectivity feature, this new interface allows
the instrument to be operated remotely with a VNC software application
from another digital device whereby the analyzer can be accessed,
controlled, data displayed etc. as if the analyzer were physically present.
Although the analyzer arrives already setup for your specific
application, a gas chromatograph mode allows the user to program the
instrument for measuring different species present in the sample.
1.1 Main Features of the Analyzer
The GC-Pro TCD Analyzer is sophisticated yet simple to use. A
touch screen display on the front panel provides access all phases of
setup, calibration, operation, and troubleshooting on the GC-Pro TCD.
The main features of the analyzer include:
Stable, accurate thermal conductivity detector for analyzing
inert gases and other species not amenable to flame
ionization detection.
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Introduction GC-Pro TCD
Data acquisition and control functions supporting:
Pressure measurements, 5-Channels (Future option)
Flow (MFC) measurements, 3-Channels (Future option)
Oxygen measurements, 6-Channels (Future option)
Temperature measurements and control, 4-Channels
6-Channel Dew point Hygrometer measurements, 6-
Channel (Future option)
Relay, (10) and solenoid outputs, (4)
Alarm, (3) and over range indication outputs, (4)
4-20mA current loop outputs, 10 channels
HMI through Maple touch sensitive display
The system operates at single phase AC, 110 or 220V 50/60
Hz (select at time of order).
High resolution, accurate readings of concentration.
Versatile analysis with three user-definable analysis ranges.
Microprocessor based electronics: 8-bit CMOS
microprocessor with 32 kB RAM and 128 kB ROM.
Auto ranging allows analyzer to automatically select the
proper preset range for a given measurement. Manual
override allows the user to lock onto a specific range of
interest.
Two adjustable concentration alarms and a system failure
alarm.
Extensive self-diagnostic testing at startup and on demand
with continuous power supply monitoring.
RS-232 serial digital port for use with a computer or other
digital communication device.
8-Analog outputs for concentration and range identification
(0-1 VDC standard and isolated 4-20 mA dc).
Superior Accuracy
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GC-Pro TCD Introduction
1.2 Principle of Operation
The analyzer uses a sample valve which is a specialized electroniccontrolled valve responsible for extracting a precise volume of sample
and delivering it to the separation column. This valve uses four micro
cavities and rotates between two positions in a timed fashion controlled
by the timing function in the control section.
The gas separation column separates the component of interest in the
sample gas based on its retention time in the packed column. Using a
carrier gas and a microprocessor actuated switching valve, the eluted gas
is analyzed using a Thermal Conductivity Detector (TCD). After each
injection cycle the column is back flushed to accept the fresh sample in
the next cycle. The result is a series of peaks over time corresponding to
the detector output for each sample cycle. The integrated area under the
peak is directly related to concentration and after signal processing, this
result is displayed in the appropriate units on the screen. The screen is
updated after each cycle.
1.3 Analyzer Description
The standard analyzer is a rack mountable instrument designed to fit
into a standard 19” instrument rack. The front interface screen is
mounted on the left side of the panel. The right side of the panel
includes the gas controls, pressure gauges and flowmeter. The front
panel is shown in Figure 1-1.
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Introduction GC-Pro TCD
Figure 1-1: GC-Pro TCD Front Panel
Gas pressure gauges and controls are mounted on the front panel
adjacent to the touch screen (human/machine interface abbreviated as
HMI) display as shown in Figure 1-1.
At the rear of the instrument are ports for the introduction of air,
zero, span, and sample gas as well as vent port connections. Three 50pin user-interface cable connectors route input/output and alarm signals
to external devices. RS232 and a network port are also available at the
rear panel for connection to a remote computer or other digital
communication device. Internally, there are two USB user connections
which are used for updating firmware to the PCBs. Figure 1-2 shows the
rear panel including the user connections.
The analyzer is set up for either 120 VAC 60 Hz or 230 50/60 Hz
operation depending on the customer’s requirements. The appropriate
power cord for your unit is included with the analyzer.
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GC-Pro TCD Introduction
Figure 1-2: GC-Pro TCD Rear Panel
Internally, there are three isothermal chambers each separately
controlled for precise control and separation of analyzed species. In the
electronics section, internal PC boards are stacked in an assembly in an
order based on inter connectivity needs between the PCBs as well as
their association with other sub assemblies distributed within the system.
See Figure 1-3.
Following is the card stack-up from top to bottom planned inside the
system
Heater card
9261 controller card
Analog data acquisition card
Analog signal conditioning card
89C5131 controller card
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Introduction GC-Pro TCD
Figure 1-3: Internal PCB Arrangement
Figure 1-4: GC-Pro TCD Internal View
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GC-Pro TCD Introduction
1.4 Applications
Monitoring the benzene concentration of carbon dioxide gas
for use in the beverage industry.
Monitoring aromatic contamination in air liquefaction and
other gas production processes.
Gas purity certification.
Detecting trace benzene in ambient air.
Detecting atmospheric pollutants.
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Operational Theory
2.1 Introduction
The GC-Pro TCD Analyzer uses a Thermal Conductivity (TC)
Detector and a Gas Chromatograph (GC) Column to separate and
analyze different factions of a volatile hydrocarbon sample. Using a
carrier gas and a microprocessor actuated switching valve, a fixed
volume of sample is pushed into the column maintained at a constant
temperature. The eluted gas is analyzed for the specific components
configured for your application using the TC detector and the column is
back flushed to accept the fresh sample for the next cycle. Actual
separating and detecting sequence may vary depending on compounds
of interest in the application for which the analyzer is configured.
The GC-Pro TCD Analyzer uses the thermal conductivity detector to
sense a variety of components that are separated through a column and
eluted to the sensor in a time sequence determined by their respective
retention time. It compares the difference in conductivity between a
known volume of injected sample driven by carrier gas at a fixed
temperature to a constant flowing reference gas. Thermal conductivity is
a fast, accurate and reproducible tool for detection and measurement
under certain conditions. In general, thermal conductivity measurements
are binary and non-specific in nature, that is, they respond to the total
difference in thermal conductivity between two samples. If the sample
contains more than two components, the thermal conductivity
measurement is ill defined and cannot be used to determine the
concentration of the mixture without extensive calibration. Similarly, if
the thermal conductivity difference between components of a binary
mixture is low, sensitivity is negatively impacted.
The GC-Pro TC Analyzer avoids these issues by coupling the TC
detector with a gas separation capability in the GC column. Therefore,
even if the sample stream contains more than one compound, at any time
during analysis only a binary mixture which includes the component of
interest based on its separation properties, plus carrier gas is delivered to
the detector. A suitable carrier gas can be selected that among other
properties, maximizes the thermal conductivity difference for enhanced
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sensitivity. And since the sampling valve is designed to inject a precise
and known volume of sample at a fixed temperature, the actual
concentration of the compound of interest can be determined.
A stainless steel packed column containing Chromosorb Diatomite
or other material depending on the application, is held at a constant
temperature. The temperature as well as the carrier gas and its pressure
are critical and depend on the application. The actual temperature
setpoint and compound separation for your instrument have been
determined at the factory. They are listed in the Addendum and Testing
Results section of Appendix C.
Using a specific carrier gas to inject the sample gas into a known in
volume, the specific component of interest elutes from the column
within a few minutes. The exact timing is characteristic of the material
and has been determined at the factory during testing. Additionally, a
clear separation is observed from other components in the sample gas
however each has a characteristic timing so the instrument can select
only the peak associated with the compound of interest for processing.
All necessary information regarding carrier gas type, sample loop
volume, temperature and pressure settings, and internal timing settings
are given in the Addendum and Testing Results section of Appendix C.
2.2 Modes of Operation
The analyzer has 2 modes of operation depending on the position of
the GC Sampling Valve (See Piping Diagram in Figure 2-2). They are:
Sample Mode (position A) and Analysis Mode (position B).
1. Valve Position A—Sampling Mode
In this mode the analyzer configures the operational valve to
back flush the column and charge the sample loop. The Sample
Mode is programmed to continue for a 7 minute period by
factory default; however, it is usually modified to match the
needs of a particular process. The specific timing interval for
your system is listed in the Addendum and Testing Results
section of Appendix C. It is possible to set the Sample Mode
duration up to 25 minutes.
2. Valve Position B—Analysis Mode
In this mode the analyzer configures the sampling valve to feed
the gas in the sample loop through the column and to the
detector. The eluted sample from the column is fed to the TC
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GC-Pro TCD Operational Theory
detector for the analysis of the compound of interest in the
stream. If configured to do so, the analyzer may read the detector
for a programmed 5 second period at some point within this
mode cycle to obtain a baseline reading for further calculation.
This mode is usually programmed to continue until the
compound of interest is fully eluted from the column. It is
possible to set it up to 25 minutes.
During the Analysis Mode, a ‘Peak Detect’ period is programmed at
which time the analyzer reads the detector output. The analyzer
integrates the peak area during this time in conjunction with the baseline
settings to calculate the concentration of the compound of interest. The
calculation is performed at the end of the ‘Peak Detector’ period and the
result is displayed at the end of Analysis Mode.
2.3 Analyzer Subsystems
The Model Analyzer is composed of four subsystems:
1. Sample System
2. GC Column
3. Detector Cell
4. Electronic Signal Processing, Display and Control
2.3.1 Sample System
All components used to control the sample and supporting gases are
located on the front panel or inside the analyzer chassis. For the internal
components, they are accessible after removing the top cover of the
analyzer. Adjustments are made to the carrier gas pressure and sample
flow using the controls on the front panel. See Figure 1-1. Other
adjustments are made using the touch screen and are described in
Section 4.
The analyzer contains three separate isothermal chambers
‘SAMPLE’, ‘Sensor’, and ‘COLUMN’ that are controlled individually.
Temperature and control information are available onscreen. See Section
4.5.7. The chambers and the switching valve are identified in Figure 2-
1.
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Figure 2-1: Internal Temperature Controllers
The sample chamber contains the 10-port GC switching valve and 2
sample loops. The ‘TC Sensor’ chamber contains the thermal
conductivity sensor. The ‘COLUMN’ is housed in a separate
‘COLUMN’ enclosure and maintained at a temperature of 70° C.
Chamber temperatures have been set at the factory however they can be
changed by the user from the Settings/Thermocouple/Settings screen as
described in Section 4.5.7.2. The actual temperature setpoint for your
instrument may be different depending on the application. It is listed in
the Addendum and Testing Results section of Appendix C.
2.3.2 Gas Flow Control System
The analyzer is equipped with ports for the introduction of carrier
gas, span, and sample gas. Depending on the application and the options
chosen, some instruments may have a separate port for admitting a purge
gas.
It is imperative that the sample, carrier and span gases be supplied at
constant pressure using two stage stainless steel diaphragm gas
regulators. The recommended pressure range is 30 to 80 psig for sample
and carrier gas; the span gas should be supplied at a pressure of 20 psig
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GC-Pro TCD Operational Theory
to the restrictor fitting either on the optional auto calibration module or
the span inlet on the rear panel.
The Piping Diagram for the standard instrument is shown in Figure
2-2. A 10-port 2-position GC sampling valve is used to control and
direct gas flows including sampling, back flush, and carrier gas. The
fixed volume sample loop ensures the same volume of sample injection
in the column every cycle.
Figure 2-2: Typical Piping Diagram Used in the GC-Pro TCD
If your instrument is fitted with the optional auto calibration module,
a separate compartment containing of a pair of solenoid valves is
installed for controlling the introduction of sample or span gas to the
detector. Calibration can be performed automatically on a programmed
schedule or manually using the front panel interface.
Other detector options are available for the GC-Pro series instrument
which may alter the appearance of the front and rear panels and include
additional gas ports such as fuel and air for the FID option. These
options, if included, will be described in an accompanying addendum to
this manual.
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2.3.3 Gas Separation System
The carrier gas pressure and column temperature are the critical
parameters in the separation process. A heater is used in column housing
and the temperature controlled by the Temperature PCB. A constant
carrier gas flow is provided by a pressure regulator on the front panel set
to a specific pressure with an inlet carrier gas supply of 80 psig at the
rear panel. Thus, a stable flow is achieved by maintaining a constant
pressure across restrictors upstream from the cell. Actual carrier gas
flow rate through the column, which is crucial for separation retention
time, will depend on the carrier gas pressure and the type of column
used for each application. It is important that all temperature and
pressure settings are set to the values listed in the Addendum and Testing
Results section of Appendix C.
2.4 Detector Cell
The thermal conductivity sensor contains two chambers, one for the
reference gas of known conductivity (which is of the same as the carrier
gas) and one for the sample gas which is driven by the carrier gas. Each
chamber contains a pair of heated filaments. Depending on its thermal
conductivity, each of the gases conducts a quantity of heat away from the
filaments in its chamber. See Figure 2-3(a).
The resistance of the filaments depends on their temperature. These
filaments are parts of the two legs of a bridge circuit that unbalances if
the resistances of its two legs do not match. See Figure 2-1(b).
Figure 2-3: Thermal Conductivity Cell Operating Principle
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