VQ548MP-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 VQ548MP-DA Datasheet MEM’s Catalytic Combustible Gas Sensor (4-Series) This datasheet describes the use of the VQ548MP-DA Pellistor. This is commonly used, but not exclusively, in mining applications. It is a low power, intrinsically safe, extremely robust and poison-resistant device in a certified flameproof enclosure. The VQ548MP-DA has been designed to provide the basic sensor performance that will enable a suitable instrument to meet the various (Group 1) mining performance standards. The VQ548MP-DA, 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. FEATURES • Low power – designed for battery operation • Small size (16 x 20 mm) • Compatible with instruments using VQ500 type sensor • High resistance to mechanical shocks • Assessed as intrinsically safe • Low orientation effect • ATEX Certified • IECEx certified 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. 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. TECHNICAL SPECIFICATION Mechanical Dimensions Body material Weight see outline, page 4 PEI 8g Environmental 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. Ambient temperature range for operation / storage: certified: Operational pressure range Humidity range for operation and storage Gases Detected −40 to +60 °C −40 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 +2.9 to +3.1V; 39 to 47mA (