Principle of operation

The ULTRAMAT 6 gas analyzer operates according to the infrared two-beam alternating light principle with double-layer detector and optical coupler.

The measuring principle is based on the molecule-specific absorption of bands of infrared radiation. The absorbed wavelengths are characteristic to the individual gases, but may partially overlap. This results in cross-sensitivities which are reduced to a minimum in the ULTRAMAT 6 gas analyzers by the following measures:

• Gas-filled filter cell (beam divider)
• Double-layer detector with optical coupler
• Optical filters if necessary

The figure shows the measuring principle. An IR source (1) which is heated to approx. 700 °C and which can be shifted to balance the system is divided by the beam divider (3) into two equal beams (sample and reference beams). The beam divider also acts as a filter cell.

The reference beam passes through a reference cell (8) filled with N₂ (a non-infrared-active gas) and reaches the right-hand side of the detector (11) practically unattenuated. The sample beam passes through the sample chamber (7) through which the sample gas flows and reaches the left-hand side of the detector (10) attenuated to a lesser or greater extent depending on the concentration of the sample gas. The detector is filled with a defined concentration of the gas component to be measured.

The detector is designed as a double-layer detector. The center of the absorption band is preferentially absorbed in the upper detector layer, the edges of the band are absorbed to approximately the same extent in the upper and lower layers. The upper and lower detector layers are connected together via the microflow sensor (12). This coupling means that the spectral sensitivity has a very narrow band.

The optical coupler (13) lengthens the lower receiver cell layer optically. The infrared absorption in the second detector layer is varied by changing the slider position (14). It is thus possible to individually minimize the influence of interfering components.

A chopper (5) rotates between the beam divider and the sample chamber and interrupts the two beams alternately and periodically. If absorption takes place in the sample chamber, a pulsating flow is generated between the two detector levels which is converted by the microflow sensor (12) into an electric signal.

The microflow sensor consists of two nickel-plated grids heated to approximately 120 °C, which, along with two supplementary resistors, form a Wheatstone bridge. The pulsating flow together with the dense arrangement of the Ni grids causes a change in resistance. This leads to an offset in the bridge, which is dependent on the concentration of the sample gas.

Notes

The sample gases must be fed into the analyzers free of dust. Condensation should be prevented from occurring in the sample chambers. Therefore, the use of gas modified for the measuring task is necessary in most application cases.

As far as possible, the ambient air of the analyzer should not have a large concentration of the gas components to be measured.

Flow-type reference sides with reduced flow must not be operated with flammable or toxic gases.

Flow-type reference sides with reduced flow and an O₂ content > 70% may only be used together with Y02 (Clean for O₂).

Channels with electronically suppressed zero point only differ from the standard version in the measuring range parameterization.

Physically suppressed zeros can be provided as a special application.

ULTRAMAT 6, principle of operation

Essential characteristics

• Dimension of measured value freely selectable (e.g. vpm, mg/m³)
• Four freely-configurable measuring ranges per component
• Measuring ranges with suppressed zero point possible
• Measuring range identification
• Galvanically isolated signal output 0/2/4 to 20 mA per component
• Automatic or manual measuring range switchover selectable; remote switching is also possible
• Differential measuring ranges with flow-type reference cell
• Storage of measured values possible during adjustments
• Time constants selectable within wide limits (static/dynamic noise suppression); i.e. the response time of the analyzer or component can be matched to the respective measuring task
• Short response time
• Low long-term drift
• Measuring point switchover for up to 6 measuring points (programmable)
• Measuring point identification
• Monitoring of sample gas flow (option)
• Internal pressure sensor for correction of variations in atmospheric pressure in the range 700 to 1 200 hPa absolute
• External pressure sensor can be connected for correction of variations in the process gas pressure in the range 700 to 1 500 hPa absolute (option)
• Two control levels with separate authorization codes to prevent unintentional and unauthorized inputs
• Automatic, configurable measuring range calibration
• Simple handling using a numerical membrane keyboard and operator prompting
• Operation based on NAMUR recommendation
• Customer-specific analyzer options such as:
  • Customer acceptance
  • TAG labels
  • Clean for O₂ service (specially cleaned gas path)
• Easy device replacement since electric connections can be simply disconnected from the device
• Sample chambers for use in presence of highly corrosive sample gases, e.g. tantalum layer or sample chamber made of Hastelloy C22 (special application)

Additional features, dual-channel version

• Separate design of physical unit, electronics, inputs/outputs and power supply for each channel
• Display and operation via common LCD panel and keyboard
• Measurement channels 1 and 2 can be converted to series connection (linking of gas connections from channel 1 to channel 2 on rear)