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reserves the right to change the specification of goods without notice. SGX accepts no liability beyond the set out in its standard conditions of sale in respect of
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SGX Europe sp .z o.o. Poland REGON: 362332227 DS-0223, Issue 2, 10-May-2016, Page 1
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VQ500 Series Datasheet
Catalytic Combustible Gas Sensor
(4-Series)
The VQ500 Series is a complete range of miniature, fully
certified, flameproof sensor heads containing a high
quality, low power pellistor pair optimised for the detection
of combustible gases or % volume gases in thermal
conductivity mode. They have an outline identical to
modern miniature electrochemical cells and are ideally
suited for use in portable instruments.
Within the VQ500 Series there are specific sensors that
are able to detect most combustible gases and vapours
and ammonia at LEL levels. The thermal conductivity
version will detect most gases at % volume concentrations
which have thermal conductivities different from that of air.
The VQ500ZD/W variants have had a temperature test
performed during its manufacture to confirm the
temperature performance of the sensor meets the
datasheet ensuring compliance to the various mining
performance standards (Group 1) with regard to the
temperature performance.
The VQ548ZD-S variant has extra burn-in for enhanced
stability.
FEATURES
• Optimised for combustible gases and vapours
• Thermal conductivity versions available
• Certified explosion proof component
• Integral pellistors
• Low power
• Standard miniature body size
• Poison resistant – silicones and hydrogen sulfide
• Shock resistant
• ATEX certified
• IECEx certified
• CSA certified
• UL recognised
• Temperature Rated between -40°C and +55°C
OPERATING PRINCIPLES
The detector consists of a fine coil of platinum wire
embedded in a ceramic bead incorporating a noble metal
catalyst. The coil acts both as an electrical heater and as a
resistance thermometer. The bead is mounted on a
header with connecting leads and is surrounded by a
metal can with the end open to the atmosphere.
If a flammable gas is present when the bead is heated to
about 400 to 500 °C, the gas will oxidise and the resultant
release of energy will heat the bead still further. This increase
in temperature is detected as an increase in resistance of the
coil.
The temperature of the coil is also affected by ambient
temperature and by variations in thermal conductivity of the
air caused by the possible presence of inert gases such as
carbon dioxide. To compensate for temperature changes not
caused by the oxidation of the flammable gas a second, inert
bead is used. This compensator is made in the same way as
a detector bead except that instead of incorporating a catalyst
in the ceramic bead, the bead is treated so that oxidation
cannot take place. The two beads are then used in a circuit
that detects the difference in their resistances. Since the two
beads are generally of a different colour, they have different
emissivity and hence different slope resistances. Therefore, to
obtain the best temperature performance, it is necessary to
connect a fixed resistor in parallel with the compensator to
correct for its higher slope resistance.
TECHNICAL SPECIFICATION
Mechanical
Environmental
Temperature range for
operation and storage
−40 to +55 °C
Humidity range for operation
and storage
(non-condensing)
Electrical
(Depending upon type)
(Depending upon type)
