VQ548MP & MP-7217
5Pages

Catalog excerpts

This datasheet describes the use of the MP-7217 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 MP-7217 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 MP-7217, whilst being optimised for its methane response (up to 5% volume in air), will also detect other flammable gases and vapours. For further information, contact SGX Sensortech. MP-7217 and VQ548MP MEMS Pellistor MP Series Low power – designed for battery operation Compatible with VQ500 head instrument High resistance to mechanical shocks ATEX/IECEX certified package OPERATION It is recommended that the detector and compensator be run in a Wheatstone bridge circuit. A suitable circuit is shown below. In use, the bridge supply voltage should be stable to within + 0.05 V, or the output in clean air may change in sympathy. Although it is generally recommended that pellistors should be run with a constant voltage supply to the bridge, it is possible to use a constant current supply provided that the voltage across the bridge in clean air remains within the recommended limits. 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 Detector device and with inert layer for 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. This 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 of a different colour, they have different emissivities 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. Recommended circuit diagram Whilst SGX Sensortech has taken care to ensure the accuracy of the information contained herein it accepts no responsibility for the consequences of any use thereof and also reserves the right to change the specification of goods without notice. SGX technologies accepts no liability beyond the set out in its standard conditions of sale in respect of infringement of third party patents arising from the use of tubes or other devices in accordance with information contained herein. In case of modification of the product, SGX disclaims all liability.

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SENSOR CONFIGURATION MAXIMUM RATINGS (Absolute values) The internal connections are shown below. Input voltages between pins: pins 2 and 3 . . . . . . . . . . . 3.2 V pins 1 and 2 . . . . . . . . . . . 1.6 V pins 1 and 3 . . . . . . . . . . . 1.6 V Connection Output Compensator Detector 2 and 3 are the two pins of the dual device MEMS pellistor (purely ohmic resistors, not polarized) Operation, storage in original packaging and shipping: Temperature . . . . . . . . . . . . . . . . . . . . . . . . . .-40 to +60 °C (certified -40 to +75° for intrinsic safety) C Humidity . . . . . . . . . . ....

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PACKAGE OUTLINE DIMENSIONS Dimensions without limit are nominal Dimensions without limit are nominal ) SGX Sensortech 2014 Document subject to disclaimer on page 1 DS-0140, Issue 1, 08-Jan-2014, Page 3 Supporting your great ideas www.pewatron.com „ m,mber of lh. *„„«*rr„„,Group

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INSTRUCTIONS SPECIFIC TO HAZARDOUS AREA INSTALLATIONS (Ref EU ATEX Directive 94/9/EC, Annex II, 1.0.6) 1. The MP-7217 and VQ548MP Gas Sensor is component approved only and may not be used as a stand-alone item in a hazardous area without further protection. 2. The component is only certified for operation in ambient temperatures between –40°C and +60° and should not C be used outside this range. For intrinsic safety the component is certified for operation in extended ambient temperatures between –40° and +75° C C. 3. For the purpose of temperature classification of the apparatus in which...

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VQ548MP & MP-7217 5Pages

Catalog excerpts

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VQ548MP & MP-7217
5Pages