Status indicators and photoelectric commands
The operational status of the instrument is indicated by the row of colored lights behind a window in the explosion proof housing. Operator commands for calibration and alarm levels are made by shining a flashlight on a photosensor behind the window while shadowing adjacent photosensors with the fingers. This feature greatly reduces the need for opening the housing.

Microcomputer electronics
The monitor is controlled by an internal microcomputer. This microcomputer provides advanced features such as interpretation of the sensor signal for optimum accuracy, user programming of alarm levels, maximum automation of user calibration and frequent diagnostics to detect, correct and report malfunctions. .In accordance with standard convention, a persistent malfunction is reported as zero voltage in the analog output. User setting and key operational data are stored in nonvolatile memory to survive power interruptions. The electronics are robust and self-reliant as appropriate for an unattended installation. For instance, a watchdog timer circuit monitors activity of the microcomputer and resets the unit if a failure is indicated. A power-fail circuit provides a safe power-down sequence and subsequent restart.

Sensor replacement and calibration
The microcomputer continually compensates for aging in the sensor’s response. Under standard operating conditions replacement of the mercaptan sensor should be made every 3-6 months to maintain optimum operating efficiency. Actual lifetime varies according to individual usage. Sensor replacement takes about five minutes. A calibration is performed at that time. This involves connecting source of ‘span’ gas having a mercaptan concentration of 20lbs/MMscf for about six minutes and entering commands with a flashlight. To ensure optimum accuracy, the unit should be recalibrated every three months. Calibration gas generator kits are available from OdorEyes technologies. Although usually calibrated on tertiary butyl mercaptan, the instrument responds identically to other commonly used mercaptan odorants.

Systems built to order
Fixed and portable OdorEyes systems are built to order, therefore the standard specifications presented here are subject to variation. Special programming is available in the instrument unit.