Infrared Gas Analyzer | ||
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3.4 Circuit Description
The Teledyne Analytical Instruments IR bench is a multiple wave- length, single beam design. It uses a quadruple detector that consists of a specially designed, patented thermopile with small IR filters mounted in front of it to produce independent voltages. These correspond to the transmission of energy at each filter’s wavelength. They are amplified by special high stability operational amplifiers to produce the output of the device.
IR energy is generated by a filament (IR source) operating at a moder- ately elevated temperature.
The cell cavity allows the sample gases to pass between the IR source and the detector. Sapphire cell windows allow passage of this IR energy with minimal absorption. The gases that pass through the cell absorb energy of the IR band at different wavelengths within the spectrum.
An optical filter is mounted on the face of each detector. Each detector responds to a particular wavelength, producing a voltage proportional to the energy that has passed through the gas and filter. If the gas concentration changes, the energy at the measuring wavelength changes, changing only the measuring voltage output. The reference voltage output is not affected by the gas concentration changes. This “measurement” voltage change is electroni- cally processed as the instrument’s output signal
IR Bench Block Diagram
Teledyne Analytical Instruments |