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The Model IR400 infrared (IR) point detector is a microprocessor-based combustible gas detector that continuously monitors combustible gases in the lower explosive limit (LEL) range and provides a 4 to 20 mA analog signal proportional to the 0 to 100% LEL concentration. The detector also monitors other conditions such as supply voltage and optical path integrity. The IR400 detection principle is based on measuring the absorption of infrared radiation passing through a volume of gas using a dual beam, single detector method. The IR detector measures the intensity of two specific wavelengths, one at an absorption wavelength and another outside of the absorption wavelength. The gas concentration is determined by a comparison of these two values. Configurations with analog output, Modbus, and HART are available. The IR400 provides a two-wire RS-485 addressable communications link conforming to the Modbus protocol that is used to monitor the IR400's status and settings in order to simplify installation and maintenance. Data available through HART or Modbus, such as configuration device settings and stored maintenance records, can be used to perform diagnostics and take corrective action before a problem occurs. The IR400 is calibrated at the factory and needs no routine field calibration. It requires only a periodic cleaning of the windows and re-zeroing to ensure dependable performance.