Mode 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 cell (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 cell and interrupts the two beams alternately and periodically. If absorption takes place in the sample cell, 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 grids heated to approx. 120 °C which, together with two further resistors, form a Wheatstone bridge. The pulsating flow together with the very close arrangement of the Ni grids leads to 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 have to enter the analyzer dustfree. Avoid condensate in the sample cells. Therefore an appropriate gas preparation is required in most applications.

The ambient air of the analyzer should be, in a large extent, free of high concentration of the component to be measured.

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

Channels with electronically suppressed zero only differ from the standard version by the measuring ranges parameterization.

Physically suppressed zeros are implemented as special applications.

ULTRAMAT 6, mode of operation

Essential characteristics

• Four freely-programmable measuring ranges per component
• Measuring ranges with suppressed zero possible
• Measuring range identification
• One electrically isolated signal output 0/2/4 to 20 mA per component
• Autoranging or manual range switching possible; remote switching is also possible
• Differential measuring ranges with flow-type reference cell
• Storage of measured values possible during calibration
• Time constants selectable within wide limits (static/dynamic noise suppression); i.e. the response time of the analyzer or the component can be matched to the respective application
• Fast response time
• Low long-term drift
• Measuring-point selection 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 600 to 1200 hPa absolute
• External pressure sensor can be connected for correction of variations in the process gas pressure in the range 600 to 1500 hPa absolute (option)
• Two-stage access code to prevent unintentional and unauthorized inputs
• Automatic range calibration can be parameterized
• Simple handling using menu-based operation with numerical membrane keyboard
• Operation based on NAMUR Recommendation
• Customer-specific analyzer versions such as e.g.:
  • Customer acceptance
  • Tag labels
  • Drift recording
• Simple analyzer exchange since electric connections are easy to remove
• Sample cell for use in presence of highly corrosive sample gases (e.g. tantalum layer or Hastelloy C22).

Additional characteristics, 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
• Channels 1 and 2 can be converted to connection in series (linking of gas connections from channel 1 to channel 2 on rear).