Thermal Conductivity Hydrogen Gas Analyzer

Features and typical applications
Model variations
Technical data

Hydrogen in (quasi) binary gas mixtures - thermal conductivity H2 gas analyzer – CONTHOS 3 - TCD

Typical Applications

  • Metallurgical process gases such as blast furnace, converter steel or direct reduction
  • Steel industry: Heat treatment & hardening
  • Petrochemistry: Gas processing to synthesis gas, reformer gas & coal gasification
  • Monitoring of gas purity, pressure swing adsorption, gas turbine cooling gas, LEL/UEL as well as inert gases
  • H2 and O2 purity in electrolysis of water

Key Features

  • Extremely long term stable analysis of H2 and noble gases in binary and quasi-binary gas mixtures with lowest and extremely suppressed ranges: 99.5 -100%
  • Ultra-fast response  T90 ≤ 3 sec
  • Highly corrosion resistant with Al2O3, glass and quartz for process gases with Cl2, HCl, H2O
  • High temperature analyzer up to 180°C for high dew points and possible salification


The CONTHOS 3 state-of-the-art thermal conductivity gas analyzer is an analytical instrument developed for on-line monitoring in process industry applications.

The special outstanding technical features of LFE's microprocessor controlled gas analyzer are:

  • High temperature version of thermal conductivity detector - thermostat controlled temperature from 50°C to max. 180°C
  • High corrosion resistance in the entire sample gas path
  • Low detection limit in the lower ppm range
  • Response highly independent of the gas flow
  • Extraordinarly high long-term stability
  • Intuitive user-interface based on NAMUR recommendations
  • Automatic self-diagnosis
  • Optional dynamic interference correction of up to 3 gases in conjunction with external, selective gas analyzer channels

High temperature and corrosion resistant TCD – thermal conductivity analyzer - CONTHOS 3 - TCD

The technical features of the unique CONTHOS 3 gas analyzer open up new areas of application for the thermal conductivity principle, as well as help to eliminate weak points in present analysis problem solving.

The high temperature versions include the complete thermostat control of the TCD detector as well as all gas lines and connectors within the analyzer. For temperatures above the sample gas dew-point in con­junction with external heated gas lines for gas inlet and gas outlet.

First developed in 1979 the LFE CONTHOS gas analyzer has proven itself in many years of continuous operation in fields such as:

  • in corrosive process gases in the chemical and petrochemical industry
  • in thermostat controlled applications
  • in all of the "classical" applications of the TCD principle with outstanding measurement performance


LFE's Thermal Conductivity Detector (TCD)

In conventional gas analyzers utilizing the principle of thermal conductivity a heated object is suspended in a volume containing the sample gas. Electrical energy passed through the object results in the object heating up and attaining an equilibrium temperature which is primarily dependent upon the thermal conduction properties of the surrounding gas. This temperature is normally measured directly as a change in the electrical resistance of the heated object itself.

LFE´s unique principle modifies this "classical" method by spatially and electrically decoupling the heated element from the temperature sensing element. The specially designed geometry of the TCD cell in conjunction with the decoupling effectively suppresses undesired competing thermal effects (i.e. free and forced convectional effects). The result is an instrument whose quick, stable response requires no compromise between gas flow and response time.


  • micro-miniaturized for quick response behavior
  • corrosion and temperature resistant
  • made of aluminum oxide (Al2O3), glass and SiOx-coated platinum sensor filaments

Corrosion and temperature resistant thermal conductivity detector – fast response TCD

Model variations

19“ rack housing for cabinet mounting – absolute and suppressed TCD ranges with interference correction
19"-rack housing
(protective class IP40)
IP65 field housing - absolute and suppressed thermal conductivity ranges for multi-component gas mixtures
field housing
(protective class IP65)
Explosion protected ATEX field housing - absolute and suppressed TCD ranges for multi-component mixtures
explosion protected
ATEX version for ex zone 1 & 2


  • Up to 3 switchable ranges: independently configurable, suppressed & absolute (non-suppressed)
  • Dynamic interference correction of accompanying components in multi-component gas mixtures in conjunction with external, selective gas analyzers
  • Digital I/O board for remote range switching, range identification, threshold contacts, etc.
  • RS-485 interface with Modbus RTU protocol
  • Heated gas lines and gas connectors within analyzer housing (max. 180°C; CONTHOS 3F only)
  • TC detector with flowing reference cell (CONTHOS 3E & 3F)

Technical Data

19”-rack housing
field housing

ATEX compliant Ex p system

Technical specifications subject to change without notice

  19“ rack housing thermal conductivity detector to analyze 0 – 0.5% H2 and 99.5 – 100% hydrogen Purgeable wall mounting housing thermal conductivity detector to analyze 0 – 0.5% H2 and 99.5 – 100% hydrogen ATEX compliant ex zone 1 & 2 Ex p housing for hydrogen measurement - CONTHOS 3 – TCD Ex p

for mounting in 19" cabinet

purgeable steel housing for wall mounting; with separate compartments for the electronic components and the analytical components

Enclosure & electrical data

(H x W x D)

133 x 483 x 427 mm
(3U / 84HP)

434 x 460 x 270 mm

490 x 460 x 270 mm

Protection class



Electrical hazardous area class


Protection type "px" for zones 1 & 2 according to EN 60079

Ex protective class of system: II 2 G, Ex p II T4


approx. 10 kg

approx. 25 kg

approx. 30 kg

Power requirements

100-240 VAC (48-62Hz; nominal voltage range: 88-253 VAC; 100 VA max. during warm-up period)

Measuring characteristics

Measuring principle

Thermal conductivity (TCD). Difference in thermal conductivity (Δλ) of various gases

Measuring ranges

Up to 3 linearized, independently configurable, switchable ranges.
Suppressed output ranges within the corresponding reference range can be easily configured.
Range switching is accomplished manually, automatically and/or remotely via optional digital inputs.

lowest range: 0 - 0.5% H2 in N2 or 99.5-100% H2 in N2 (or equivalent Δλ)
largest range: 0 - 100% H2


Manual: 2-point (zero / span) calibration
Option: automatic or remote calibration in conjunction with the optional digital I/O-board or RS-485

Warm-up time

dependent upon TCD operating temperature as well as the ambient temperature:
70°C: approx. 20 min.; 140°C: approx. 90 min.

Response time t90

≤ 3 sec (at 60 l/h gas flow and minimum signal dampening level)

Influence of gas flow

between 3 - 30 l/h: < 0.5% of range span for a gas flow change of ±10 l/h
between 30 - 60 l/h: < 1% of range span for a gas flow change of ±10 l/h

Higher flow rates up to e.g. 120 l/h are possible. At these higher flow rates it is recommended that the analyzer be calibrated at the operating flow rate.

Pressure influence

The TCD principle has a normally negligible pressure dependency. At very low ranges it can be seen as a proportional signal offset.

Gas specific order of magnitude: < 0.02% H2 equivalent per 100 mbar

Optional pressure compensation is available (not for Ex p instrument) should the residual pressure influence be an issue at very low ranges.

Detection limit 1

≤ 0.5% of span (at signal dampening level: 1 sec)

Linearity/ Accuracy 1

≤ 0.5% of span

Reproducibility 1

≤ 0.5% of span

Response drift 1

Zero: ≤ 1% of span per week
Span: ≤ 1% of span per week

Ambient temperature influence

Zero: ≤ 1% of span per 10 K
Span: ≤ 1% of span per 10 K

Ambient temperature in operation

allowed temperature range : +5 to +45°C

Influence of inclination

no influence

Materials in contact with sample gas


19" rack housing

field housing

ATEX compliant Ex p system


Al2O3-ceramic and sapphire, glass and SiOx-coated Pt-measuring filaments
high corrosion- and temperature-resistance

Internal gas lines

standard: PTFE

optional: stainless steel tubing (SS 321; similar to 1.4541) and 1.4571

standard: PTFE

optional: stainless steel tubing (SS 321; similar to 1.4541)

stainless steel tubing
(SS 321; similar to 1.4541)

Sample gas connectors

Standard: stainless steel (SS 316; similar to 1.4401)

Standard: Swagelok® connectors for ø6mm tubing

Optional: Swagelok® connectors for ø¼" tubing

Optional: NPT ¼" (female)

Standard: Swagelok® connectors for ø6mm tubing

Optional: Swagelok® connectors for ø¼" tubing

Standard: Swagelok® connectors for ø6mm tubing

Optional : PFA connectors for synthetic tubing DN 4/6
(only in conjunction with PTFE tubing)


Data display, inputs and outputs

User Interface

LC-display (40 characters x 16 lines) + bar graph

Plain text description of instrument status as well as digital status output

Language: switchable between English & German

Analog signal output

2 independently configurable, galvanically isolated analog outputs (with common ground; RLoad = 600 Ohm max)

Available output levels: 0 - 20 mA, 4 - 20 mA, 4 - 20 mA with superimposed instrument status (NAMUR NE 43 compliant) as well as test signal levels (0, 4, 10, 12 & 20 mA)

Digital outputs
1 to 3
(instrument status)

Instrument status (NAMUR NE 107 compliant) via floating contacts (28 V max.; 350 mA max.)


Analog inputs

3 galvanically isolated, configurable analog inputs for interference correction
0 - 20 mA or 4 - 20 mA (Ri = 50 Ohm)

Interference correction

3 correction channels for static and/or dynamic interference correction (dynamic correction only in conjunction with the optional analog inputs or RS-485)

Digital I/O

Digital inputs: 8 configurable, optically isolated inputs (6 - 24 VDC; 10 mA max.)

  • remote range selection
  • remote triggering of zero and span calibration
  • remote triggering and cancelling of automatic calibration
  • switching of interference correction analog inputs to a secondary input range
  • mapping of user defined input to a digital output

Digital outputs: 7 configurable, floating relay contacts (28 V max.; 350 mA max.)

  • threshold monitoring (1 threshold per measuring range)
  • feedback as to the current range
  • calibration gas selection
  • mapping of user defined input to a digital output

(Note: The digital I/O board cannot be used in conjunction with the RS-485 serial interface hardware.)


with Modbus communications protocol; galvanically isolated interface
(Note: The RS-485 serial interface hardware cannot be used in conjunction with the digital I/O board.)

Service interface

non-isolated serial interface for accessing the instrument's configuration via a proprietary PC software

1 at constant temperature and pressure


  • The stability data is valid for analyzer operation with pure bottled gases. Instrument accuracy is based on binary or quasi-binary gas mixtures. Deviations from the above data can occur in conjunction with process gases depending upon the gas quality and the degree of gas handling.
  • Unless otherwise specified the CONTHOS gas analyzer is neither ex-proof nor intrinsically safe in terms of explosion protection.
  • The CONTHOS may not be employed for the analysis of ignitable gas-mixtures. The customer must ensure compliance with applicable regulations when using the analyzer with inflammable or toxic gases or when installing within explosion endangered environments.
  • The customer must ensure that the sample gas is dry and free of particulates.

Downloads  EN

CONTHOS 3-TCD | Thermal Conductivity Gas Analyzer

Application questionnaire

CONTHOS 3 - Application Data Sheets

Application data sheet
Application data sheet
Application data sheet
Application data sheet
Application data sheet

General information

Product overview

Technical specifications subject to change without notice

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