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Technical Article: Not all IR gas detectors are the same

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Our IR gas detectors differ from all other models, because they utilise silicon based solid-state IR sources. The complete opto-mechanical design and construction is so stable that an ultra-fast speed of response can be achieved whilst providing unparalleled service life and detector stability, thus saving on maintenance and service costs.

The Simrad GD10P roots go back to Simrad Optronics, a world leading Norwegian manufacturer of night vision equipment since 1960’s. They have mastered the use of the IR technology. In the early 1980’s Oil & Gas operators approached them for a solution to replace problematic catalytic gas detectors. The very first IR gas detector model was introduced in 1986 and it was an instant success with offshore operators. This makes Simtronics as one of world most proven IR gas detection technologies. The Simtronics GD10 Detectors are sold with an unmatched 15 years warranty on the SimSource™ IR sources.

The GD10P concept is based on measurement of IR radiation passing through a volume of gas. It employs a dual beam, dual wavelength measuring principle with separate optical detectors for maximum stability and reliability. Using two solid-state IR sources instead of a filament lamp ensures high reliability and long-term stability with no regular maintenance or calibration required.

Radiation from two infrared sources passes through two narrowband filters selecting a measuring wavelength and a reference wavelength. The sources are electronically chopped. Radiation is divided by a beam splitter into an internal and external path. The internal path is viewed by the compensation detector, and the external path is viewed by the measuring (main) detector. The compensation detector monitors and compensates for drift in sources or detectors. The main detector monitors the external measuring path and detects whether the selected gas is present. 

The four signals, two from the compensation detector and two from the main detector, are amplified, digitised and fed to the microprocessor. The signals are used by the microprocessor to calculate the gas concentration. The gas response is then linearized and presented as a voltage, a current or a digital output signal. Internal signals are compared with test limits to monitor electronics and optical parts. If values outside the test limits are found, specific error messages are given.

Optical filter characteristics remain constant over time, and drift in the other components is monitored and compensated by the dual wavelength, dual path concept. This means that the zero and gas span factory calibration will remain stable regardless of component drift, and that the detector needs no manual recalibration after factory calibration.

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The unique SimSource™ is a Simtronics patented solid state Silicon IR source used in all Simtronics IR gas detectors. This technology makes the GD10P the only Point IR Gas detector that does not require field calibration or recalibration during its lifetime. The GD10P has no user adjustable parts. It has been designed to require a minimum of maintenance. The only necessary maintenance is to inspect visually that the Weather Protection is not clogged in heavily contaminated areas.

In addition the GD10 uses Lead Selenide detectors which are much more stable when exposed to rapid temperature changes than Pyroelectric sensors used in other IR gas detectors. Lead Selenide will NOT give false readings if the detector is exposed to vibration.

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