OEM Thermal Conductivity Detector (TCD)

Features and typical applications
Technical data

LFE OEM Thermal conductivity detector (TCD)

Key Features

  • Quick response - T90 ≤ 3 sec
  • Extremely suppressed ranges
  • High corrosion resistance
  • High temperature capability up to 180°C
  • Infallible containment
  • Integration into Ex d housings

Typical Applications

  • Metallurgical process gases - blast furnace
  • Steel - heat treatment & hardening
  • Petrochemistry - synthesis & reformer gas
  • Gas purity - PSA, LEL/UEL & inert gas
  • H2 & O2 purity – water electrolysis
  • Synthesis & reformer gas
  • Coal, wood & biogas gasification
  • Corrosive process gases with Cl2, H2S and HCl
  • Processes with H2, water vapor and high dew points
  • Processes in hazardous areas


LFE's unique thermal conductivity detector is the heart of LFE's CONTHOS process TCD gas analyzer and has proven itself since 1979 in a wide range of applications. The TCD combines quick response, high corrosion-resistance and high-temperature capability without compromise. Further features are its extraordinary measurement stability, low range capabilities as well as highly suppressed ranges.

LFE OEM Thermal conductivity detector - TCD


LFE's thermal conductivity detector is available in an OEM (original equipment manufacturer) version which can be implemented into a customer's gas analyzer (system). The TCD OEM version can be integrated into in a standalone instrument or be used to complement other analysis principles such as for example NDIR/UV, Laser, or FTIR.

Due to its high temperature capability LFE's OEM TCD can be integrated into thermostat controlled analyzer systems (e.g. 80 - 120°C) or close-coupled to customer high-temperature systems (up to 180°C).

Such a combination of high-temperature NDIR/UV with LFE's high-temperature TCD has been approved in several tough process control applications from a well-established process analyzer company with high-temperature solutions between 80° and 180°C since 1985.

Meanwhile the OEM version of the LFE TCD has been optimized making it attractive for more companies to round off their gas analysis portfolios.

A special infallible (fail-safe) OEM version of the TCD is available for flammable and even explosive gases requiring special measures to be fulfilled.


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

Technical Data

Technical specifications subject to change without notice

Electrical interface

Power requirements

24 VDC; 35 VA max. (during initial heat-up phase)

Data / service interface

Serial interface: RS232 in conjunction with isolated logic level converter


  • Data block (proprietary protocol) includes raw value, system values such as TCD temperature, detector status and CRC
  • Data in binary or plain text form
  • Data block transmission on request or continuously

Dimensions and Weight


refer to dimensional diagram found in product data sheet


1.2 kg

Materials in contact with sample gas

TC Detector

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

Gas lines

Standard model with synthetic tubing: PTFE/PFA

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

Measuring characteristics


Note: The technical data is valid for operation of the OEM TCD within LFE's CONTHOS gas analyzer.

The overall performance data for a particular implementation may depend on the chosen system integration, interfacing and signal processing options.

Measuring principle

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

Measured quantity Concentration of a particular gas component in binary and quasi-binary mixtures
Gas interference

For the analyzer configuration, the knowledge of the sample gas composition is necessary. In complex (non-binary) gas mixtures, the measurement results may be affected by interfering components.

Through the use of dynamic interference correction, the interference effects can be suppressed under certain circumstances. This must be implemented by the customer within his system or in conjunction with the appropriate optional interface expansion modules.

Physical interference suppression is sometimes possible with certain gas combinations due to the wide temperature range of the CONTHOS' TC detector.

Measuring ranges

Measured value signal output as raw value
2nd and 3rd ranges as option
Optimized suppressed output ranges can be configured by the factory.

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


The device outputs RAW values that are neither fine-calibrated nor linearized. The customer must provide the appropriate algorithms.

Detector operating temperature

TCD standard operating temperature: 70°C
Depending on the application, the operating temperature can be factory set to 60-180°C.

Warm-up time

dependent upon TCD operating temperature as well as the ambient temperature:
70°C: approx. 20 min.; 180°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.
Strong gas flow fluctuations should be avoided.

Pressure drop approx. 0.7 mbar at 60 l/h N2

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

Detection limit 1

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

Reproducibility 1

≤ 0.5% of span

Response drift 1

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

Influence of inclination

no influence

Sample gas requirements

Sample gas temperature

min.: +5°C
max.: 10°C below detector thermostat temperature (typically 70°C)

Sample gas dew point

Dew point low enough so as to prevent condensation in the gas paths under all ambient temperature conditions

Particles in sample gas

The sample gas must be free of particles and aerosols.

Sample gas pressure

max. 300 mbar above atmospheric pressure

Sample gas flow

minimum: 3 l/h
maximum: 120 l/h
recommended: 30 - 60 l/h

1 at constant temperature and pressure


  • NOTE 1: All application and implementation details such as e.g. ranges and interfacing options must be clarified with manufacturer and evaluated for feasibility.
  • NOTE 2: The technical data is valid for analyzer operation with pure bottled gases. Instrument specifications are 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 sample handling.
  • NOTE 3: The LFE OEM TCD is neither explosion-proof nor intrinsically safe in terms of explosion protection.
  • NOTE 4: The LFE OEM TCD may not be employed for the analysis of ignitable gas mixtures. The customer must ensure compliance with applicable regulations when using the unit with flammable or toxic gases or when installing within hazardous areas.
  • NOTE 5: The customer must ensure that the sample gas is dry and free of particulates.

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OEM Thermal Conductivity Detector (TCD)


      pdf LFE Product Overview


Product Data Sheets

      pdf LFE OEM TCD | OEM Thermal Conductivity Detector

Technical specifications subject to change without notice

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