Measuring principle

The measurements are based on the molecular-specific absorption of infrared radiation bands (absorption bands).

ULTRAMAT 7 modules use a spectral range which includes wavelengths of 2 to 9 µm. Although the absorbing wavelengths are characteristic of individual gases, they may partially overlap. This results in cross-sensitivities which are reduced to a minimum by the following measures:

• Beam splitter (gas filter)
• Double-layer detector, each gas compartment with adjustable weighting between the first and second detector layer
• Application-specific pre-installed interference filter

Principle of operation

ULTRAMAT 7 modules operate according to the infrared push-pull chopped radiation principle and are equipped with a double-layer detector.

A source with a temperature of approx. 600 °C generates infrared radiation which is emitted in the beam splitter. The beam splitter acts as a filter chamber and divides the beam equally between the sample gas and reference gas compartments.

The chopper produces a periodic modulation of the infrared radiation, and thus enables relaxation of the detector.

The reference beam passes through the reference chamber and enters the detector chamber virtually unattenuated. The detector chamber is filled with a precisely defined concentration of the gas component to be measured. The sample beam, in contrast, passes through the sample chamber filled with sample gas and enters the detector chamber attenuated to various degrees. The degree of attenuation depends on the respective sample gas concentration.

The detector is designed as a double-layer detector. The detector layer at the source end serves primarily to absorb the middle of the band. The band edges, however, are absorbed equally by both of the layers.

The detector layers at both compartments of the detector are pneumatically connected to each other via a microflow sensor. This sensor element converts the pressure difference in the detector into an electrical signal.

The weighting between the first and second detector layer is preset at the factory depending on the application. The influence of interfering components is minimized as a result. To ensure the long-term stability of the measured value, the ULTRAMAT 7 module supports the predictive self-diagnostics of the analyzer. This function enables you to plan maintenance measures in a timely manner.

ULTRAMAT 7, principle of operation of the infrared channel

Essential characteristics

• Dimension of measured value freely selectable (e.g. vpm, mg/m³)
• Four freely-parameterizable measuring ranges per component
• Measuring ranges with suppressed zero point possible
• Measuring range identification
• Autoranging or manual measurement range switchover possible; 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 4 measuring points (programmable)
• Measuring point identification
• Internal pressure sensor for correction of atmospheric pressure fluctuations in the range 700 to 1 200 hPa absolute
• Automatic measuring range calibration can be configured
• Operation based on NAMUR recommendation
• Preventive maintenance / IR source monitoring