Bacharach MGS-400, Руководство пользователя

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1100-2294 Rev 1 44
It may be necessary to check the calibration if the sensor has been exposed for a long time to a
high concentration of flammable gases, vapors, or the above-mentioned contaminating
substances.
The nature of catalytic bead sensor technology means that sensor drift may typically be up to
±5% LEL per month. Instruments using these sensors should be zeroed regularly following the
instructions in section 5 of this manual.
6.1.3 Semiconductor Sensors
Semiconductor or metallic oxide sensors (MOSs) are among the most versatile of all broad-range
sensors. They can be used to detect a variety of gases and vapors in low ppm or even combustible
ranges. The sensor is made up of a mixture of metallic oxides. They are heated to a temperature
between 150º and 300º C depending on the gas
(es) to be detected. The temperature of operation
as well as the “recipe” of mixed oxides determines the sensor selectivity to various toxic gases,
vapors, and refrigerants. Electrical conductivity greatly increases as soon as a diffusion process
allows the gas or vapor molecules to come in contact with the sensor surface. Water vapor, high
ambient humidity, temperature fluctuations, and low oxygen levels can result in higher readings.
IMPORTANT: Certain substances in the environment to be monitored may
impair the sensitivity of the sensors:

Materials containing silicone or silicone rubber/putty

Corrosive gases such as hydrogen sulfide, sulfur oxide, chlorine, hydrogen
chloride, etc.

Alkaline metals, salt water spray.
6.1.4 Infrared Sensors
The infrared (IR) gas sensor is designed to measure the concentration of combustible gases and
vapors in the ambient air. The sensor principle is based on the concentration-dependent
absorption of infrared radiation in measured gases.
The monitored ambient air diffuses through a sintered metal material into the enclosure of an
optical “bench”. The broadband light emitted by an IR source passes through the gas in the optical
bench and is reflected by the walls from where it is directed towards a dual-element detector. One
channel of the detector measures the gas-dependent light transmission, while the other channel
is used as a reference. The ratio between measurement and reference signal is used to determine
the gas concentration. Internal electronics and software calculate the concentration and produce
an output signal.