Teledyne 238 User Manual
Thermal Conductivity Analyzer
OPERATING INSTRUCTIONS
FOR
Model 235 Series
THERMAL CONDUCTIVITY ANALYZER
235
236
237
238
DANGER
HIGHLY TOXIC AND OR FLAMMABLE LIQUIDS OR GASES MAY BE PRESENT IN THIS MONITORING SYSTEM.
PERSONAL PROTECTIVE EQUIPMENT MAY BE REQUIRED WHEN SERVICING THIS SYSTEM.
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
P/N M32845
08/06/99
ECO # 99-0323
i
Model 235
Copyright © 1999 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 91749-1580.
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 user, and serves as a tool by
which 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, with the
process being measured, be properly trained in the process itself, 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 (TAI), 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.
Teledyne Analytical Instrumentsii
Thermal Conductivity Analyzer
Table of Contents
1 Introduction (Models 235, 236, 237, 238)
1.1 Electronic Circuitry ...................................................... 1-2
1.2 Plug-in Circuit Boards.................................................. 1-3
1.2.1 T.C. Cell Power Supply/Amplifier Board ........... 1-3
1.2.2 Differential Power Supply Board.......................1-3
1.2.3 Alarm Comparator Board (optional).................. 1-3
1.2.4 E to I Converter Board (optional)......................1-3
1.2.5 Linearizer Board (optional) ............................... 1-4
1.2.6 220 to 240 Volt Operation (optional) ...................1-4
2 Installation
2.1 Location....................................................................... 2-1
2.2 Electrical Connections.................................................2-1
2.3 Gas Connections......................................................... 2-2
2.3.1 Reference and Zero Gas .................................. 2-2
2.3.2 Vent Lines........................................................ 2-2
2.4 Pressure Regulation.................................................... 2-3
2.5 Accessory Sample System Components .................... 2-4
2.6 Recommended Flowmeter Readings .......................... 2-5
3 Operation
3. 1 Preliminary ..................................................................3-1
3.2 Gas Flowrate............................................................... 3-1
3.3 Zero Standardization................................................... 3-1
3.4 Span standardization .................................................. 3-2
3.5 Onstream Operation.................................................... 3-2
3.6 Normal Operation........................................................ 3-3
3.7 Maintenance................................................................ 3-3
4 Linearizer
4.1 Theory of Operation ....................................................4-1
4.2 Output Signal Reversal ............................................... 4-3
Appendix
Spare Parts List ................................................................... A-1
Calibration Data ................................................................... A-2
Drawing Package................................................................. A-3
Teledyne Analytical Instruments
iii
Model 235
DANGER
COMBUSTIBLE GAS USAGE WARNING
This is a general purpose instrument designed for usage in a
nonhazardous 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.
The customer should ensure that the principles of operating of
this equipment is 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.
Teledyne Analytical Instrumentsiv
Thermal Conductivity Analyzer Introduction 1
Introduction (Models 235, 236, 237, 238)
The 235 Series Thermal Conductivity Analyzers measure the concentration of one component in a binary stream of gas, or the purity of a sample
stream containing a composite mixture of impurities, by comparing the
difference in thermal conductivity of the sample stream with that of a
reference gas of fixed composition.
Control of the sample and supporting gases is not provided for in the
basic design TAI offers a variety of supporting gas control panels as companion accessories to the analyzer to fill this need. In any case, means must
be provided for controlling the flowrates through the sample and reference
paths of the analyzer, and a control manifold will be required for the introduction of zero and span gas, as well as sample gas, into the sample path.
Appropriate pressure reducing regulators will have to be installed at all gas
supply sources; for those customers wishing to incorporate their own
sample controls, a recommended system piping schematic is included among
the drawings at the rear of the manual.
Thermal conductivity measurements are non-specific by nature. This
fact imposes certain limitations and requirements. If the user intends to
employ the analyzer to detect a specific component in a sample stream, the
sample must be composed of the component of interest and one other gas in
order to be accurate.
If, on the other hand, the user is primarily interested in the purity of a
process stream, and does not require specific identification of the impurity,
the analyzer can be used on more complex mixtures. The impurities, then,
can be a composition in themselves.
Teledyne Analytical Instruments
1-1
1 Introduction Model 235
Because analysis by thermal conductivity is not an absolute measurement, standardization gases of known composition will be required to fix
the upper and lower parameters of the range (or ranges) of analysis. These
gases will be used to periodically check the accuracy of the analyzer.
The difference in thermal conductivity between the fixed reference gas
and the sample is sensed by hot wire elements. The elements are mounted in
a cell assembly so that one set is in the reference and the other in the sample
stream. Each set of elements is a component in an electrical bridge circuit.
During calibration, the bridge circuit is balanced in zero and reference
gas at one end of the measurement range, and sensitized in reference and
span gas at the other end, so that intervening points along the range (or
ranges) of interest will produce a DC electrical signal representative of the
analysis. The resulting electrical signal is fed to an amplifier and span pot,
which produce a standard 0-1V output signal. An E to I converter PC board
is also installed and produces an isolated 4–20 mA DC current output in
addition to the voltage output.
The temperature of the measuring cell is regulated to within 0.1 degree
C by a sophisticated control circuit. A thermistor is used to measure the
temperature, and a zero-crossing switch regulates the power in a cartridgetype heater. Temperature control is precise enough to eliminate diurnal
effects in the output over the operating ranges of the analyzer.
The overall design of the instrument is intended to facilitate servicing
and troubleshooting, should that ever be necessary. The controls are all
mounted on the front panel, which can swing down, allowing access to the
cell compartment. The cell is enclosed in an insulated compartment that is
readily removable from the chassis; the electronics are mounted on a series
of circuit boards at the rear of the enclosure, accessible by removing the
back panel.
Explosion-proof models of the series use sealed explosion-proof
enclosures for the analysis section (Model 237) or both the analysis section
and control unit (Model 238). Model 235 is general purpose with remote
control unit, and Model 235 is general purpose with integral control unit.
1.1 Electronic Circuitry
The electronic components are mounted on a number of circuit boards
that plug into sockets on a larger board, dubbed the “Mother Board”. This
allows for rapid troubleshooting and repair of any defective parts, and also
for rapid field installation of optional features not ordered with the unit.
1-2
Teledyne Analytical Instruments
Thermal Conductivity Analyzer Introduction 1
All electrical interconnections are made to the terminal strips on the
mother board; this board also contains an unusual feature — a series of
regularly-spaced holes in a rectangular pattern, known as a “kludge” space,
is set aside for the installation of circuitry for special customer requirements.
1.2 Plug-in Circuit Boards
Several options are available as convenient plug-in circuit boards;
although these may not all be present in the specific instrument under
consideration, a brief description of some of the more common ones is
offered below, and noted as (optional); PC boards which are not noted as
(optional) are standard features.
1.2.1 T.C. Cell Power Supply/Amplifier Board
This circuit contains an IC regulator that holds the voltage through the
cell to 4.5 V. It also contains a 2-stage IC amplifier, with range resistors.
1.2.2 Differential Power Supply Board
15 Volts, regulated (for electronic amplifiers, etc.), and +24 volts, nonregulated (for alarm and relay circuitry and certain other functional uses) are
supplied by this circuit.
1.2.3 Alarm Comparator Board (optional)
The comparator alarm circuit is available in single or dual configurations, which can be supplied as high or low alarms, energized above or
below setpoint; adjustment of each alarm setpoint is made using a potentiometer provided on the instrument’s front panel. Power failure or “fail-safe”
alarming can also be provided. Refer to the specifications covering one
individual analyzer for details regarding specific alarm or other optional
provisions.
Teledyne Analytical Instruments
1-3
1 Introduction Model 235
1.2.4 E to I Converter Board (standard)
The standard current output in the form of an isolated 4–20 mA dc
current is supplied by the E to I converter circuit. The output of this board
is proportional to the percentage of range, for example, 4 mA for 0% and
20 mA for 100% of range. This current output is in addition to the 0–1 V dc
voltage output.
1.2.5 Linearizer Board (optional)
An excellent alternative to the use of correction curves is available as
an option with the Series 235 Analyzer. A digital linearizer circuit is available as a plug-in PC board. This is a very flexible circuit that produces a
linear correction to a wide variety of non-linear curves. The result is an
output signal which is linear over the specified analysis range or ranges.
When employed, the digital linearizer is transparent to the user and requires
no adjustment.
1.2.6 220 to 240 Volt Operation (optional)
The Series 235 analyzer is available for either 110-120 (standard) or
220-240 (optional), 50 or 60 Hz operation.
1-4
Teledyne Analytical Instruments
Thermal Conductivity Analyzer Installation 2
Installation
2.1 Location
The analyzer should be installed where it will not be subject to the
following conditions:
1. Direct sunlight
2. Drafts of air
3. Shock and vibration
4. Temperatures below 30° F or above 110° F
The analyzer should be placed as close as possible, subject to the above
conditions, to the sample point to minimize the effects of sample line lag
time on the analysis.
An outline diagram, showing the location and identification of the gas
line and electrical conduit connections, as well as the physical dimensions of
the analyzer case, is included in the drawings at the rear of the manual.
2.2 Electrical Connections
A single-phase, 110 to 120 Volt, or 220 to 240 Volt, 50 or 60 Hz line,
capable of delivering 2-1/2 amperes of current continuously, is required to
operate the analyzer. Primary power connections are made on the terminal
strip mounted on the mother board, behind the rear access cover. A solid
water-pipe ground should be provided for personnel protection. When
connecting the power source, polarize the connections as indicated on the
interconnection diagram at the rear of the manual.
Teledyne Analytical Instruments
2-1
2 Installation Model 235 Series
Use 2-conductor shielded cable (nominally No. 22 wire size) to interconnect the analyzer output signal with the recording equipment. The shield
should be terminated on the appropriate terminal (see interconnection
diagram) at the analyzer—and be left disconnected at the recorder.
2.3 Gas Connections
Customer gas connection points are located on the underside of the
analyzer case. (Standard, basic instrument)
(See Outline Diagram for identification of each point.)
2.3.1 Reference and Zero Gas
A constant supply of gas, of a fixed composition, is needed as the
reference to which the sample gas will be compared. The reference gas is
normally selected to represent the main background of the analysis. For
certain applications, an optional sealed air reference is available where the
reference side of the detector cell is filled with air and sealed. This eliminates the need to have reference gas constantly passing through the cell. For
instruments equipped with the optional sealed air reference, there will not be
reference inlet or vent ports.
A supply of gas, containing little or none of the components of interest,
is required to zero-standardize the analyzer.
In order to satisfy the requirements, both of these gases must be
supplied from purchased cylinder sources — as no other economical means
is readily available that will guarantee the user that impurities are maintained
at a low, fixed level.
Because most cylinder gases are supplied 99.95 to 99.98% pure, TBE
recommends that one cylinder of gas be used to fill both needs for most
applications (i.e., zero and reference.)
Specific recommendations as to the number and type of supporting
gases required will be found listed in the calibration section of the manual.
It is essential to the accuracy of the analyzer that the purity of the zero
gas be known. The zero control would be adjusted during zero standardization, so that the recorder indicates the impurity content of the zero gas,
rather than zero.
2-2
Teledyne Analytical Instruments
Thermal Conductivity Analyzer Installation 2
2.3.2 Vent Lines
The selected gas introduced into the sample path of the cell (zero,
span, and sample) is vented from one connection at the bottom of the
analyzer, and the reference gas is vented from another.
If it is desirable to carry these gases to an area remote from the analyzer to vent them, the following precautions will have to be observed in
vent line installation:
1. The vent lines should be constructed of 1/4 inch tubing, so that
no appreciable back pressure resulting from restricted flow is
experienced by the analyzer.
2. Both the sample and reference lines must be vented into an area
where the ambient pressure is the same.
3. The ambient pressure in the vent area must undergo no more
than normal barometric pressure changes.
4. The vent lines must be installed so that water and dirt cannot
accumulate in them.
2.4 Pressure Regulation
All incoming gas lines should be equipped with pressure regulators.
The sample line pressure regulator should be installed as close to the
sample point as possible to minimize sample line lag time.
Sample pressure should be set somewhere between 5 and 50 psig—10
psig is nominal.
To minimize flowrate adjustments, the pressure regulators on the
supporting gas supply cylinders should be adjusted to provide the same
output pressure as the sample line regulator.
When installing pressure regulators on supply cylinders, crack the
cylinder valves so that gas is flowing during installation. Using this procedure will eliminate the most common cause of standardization gas contamination. Air trapped during assembly can, and will, diffuse back into the
cylinder. This is particularly important in applications where impurities of 1
and 2% are the range of interest.
Teledyne Analytical Instruments
2-3
2 Installation Model 235 Series
2.5 Accessory Sample System Components
An integral gas selector panel is available as an option. This panel
mounts the gas controls on a panel where they can be operated conveniently
In applications where TBE furnishes an accessory gas control panel, or
a completely interconnected panel or cubicle system, installation can be
simply accomplished by using the supporting drawings included at the rear
of the manual. However, if the customer is selecting and interconnecting his
own gas system components, the following conditions should be adhered to:
1. Do not deviate from the system outlined in the piping schematic
when constructing your system.
2. Select a flowmeter capable of resolving 0.08 SCFH (40 to
50 cc/min) for the reference path of the analyzer.
3. Select a flowmeter capable of resolving 0.3 SCFH (150 cc/min)
for the sample path of the analyzer. (See Addendum A for
recommended flowmeter readings for gases heavier or lighter
than air.)
2.6 Recommended Flowmeter Readings for
Gases Heavier or Lighter Than Air
Due to the wide range of applications and gases that are measured with
the Thermal Conductivity Analyzer, the density of different sample gases
may vary considerably; for example, air is more dense than hydrogen. When
setting the sample and reference flowrate, note that gases lighter than air
will have an actual flowrate higher than indicated on the flowmeter, while
gases heavier than air will have a lower actual flowrate. The following chart
(with hypothetical figures) illustrates this fact:
GAS FLOWMETER ACTUAL
READING FLOWRATE
Lighter than air 0.3 SCFH 1.2 SCFH
Heavier than air 0.3 SCFH 0.2 SCFH
Air 0.3 SCFH 0.3 SCFH
2-4
Teledyne Analytical Instruments
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