OEM Thermal Conductivity Detector (TCD)

Dimensions

refer to dimensional diagram found in product data sheet

Weight

1.2 kg

Power requirements

24 VDC; 25 VA max. (during initial heat-up phase)

Data / service interface

RS232 or Ethernet (Telnet protocol) 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

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

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
2^nd and 3^rd 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

Calibration

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

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 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

Materials in contact with sample gas

TC Detector

Al₂O₃ ceramic and sapphire, glass and SiO_x-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)