MP7227-DA

SGX Europe Sp. z o.o. Building 11 Ligocka St. 103, 40-568 Katowice, Poland T: +48 (0) 32 438 4778 E: sales.is@sgxsensortech.com www.sgxsensortech.com MP7227-DA Datasheet Miniature MEMS Catalytic Combustible Gas Sensor The MP7227-DA pellistor is a low power, hazardous area safe, extremely robust and poison-resistant device in a certified flameproof enclosure. The MP7227-DA type sensor is designed for low power operation in continuous mode providing additionally ultra-low power consumption when used in pulse mode operation, which makes this sensor a preferred choice for battery operated devices. The MP7227-DA has been designed to provide the basic sensor performance that will enable a suitable instrument to meet the various (Group 1) mining and industrial (Group 2) performance standards. The compensator is made in the same way as a detector device except that instead of incorporating a catalyst in the coating layer, the device is treated so that oxidation cannot take place. Whilst being optimised for its methane response (up to 5% volume in air), will also detect some other flammable gases and vapours. For further information, contact SGX Sensortech. Small size and ultra-low power consumption in pulsed operation mode make the proposed sensor a preferred choice for applications where size and long battery operation are essential. The two devices are then used in a circuit that detects the difference in their resistances. Since the two devices are generally a different colour, they have different emissivity and hence different slope resistances. Therefore, to obtain the best temperature performance, it is necessary on occasion to connect a fixed resistor in parallel with the compensator to correct for its higher slope resistance. FEATURES TECHNICAL SPECIFICATION • Low power – designed for battery operation • Small size (14.4 x 6.7 mm) • High resistance to mechanical shocks • Low orientation effect • ATEX Certified (II 1G Ex da IIC Ga, I M1 Ex da I Ma) • IECEx certified (Ex da IIC Ga, Ex da I Ma) OPERATING PRINCIPLE The silicon pellistor structure consists of a pair of accurately micro machined diaphragms with two embedded planar heater meanders coated with a layer incorporating a noble metal catalyst for the detector device and with inert layer for the compensator device. The meander acts both as an electrical heater and as a resistance thermometer. The device is mounted on a PCB with wire bonding and is surrounded by a plastic can with the end open to the atmosphere. If a flammable gas is present when the device is heated to about 400 – 500 °C, the gas will oxidise and the resultant release of energy will heat the device still further. This increase in temperature is detected as an increase in resistance of the meander. The temperature of the meander 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 device is used. Mechanical Dimensions Body material Weight see outline, page 4 PEI 1g Environmental Ambient temperature range for operation / storage: certified: Operational pressure range Humidity range for operation and storage Gases Detected −20 to +60 °C −20 to +60 °C 70 to 130 kPa 0 to 95% (non-condensing) Most flammable gases and vapours Electrical DC supply to detectors Typical power Mode of Operation (1) +2.9 to +3.1V; 37.0 to 41.0 mA (