SGX Europe Sp. z o.o. T: +48 (0) 32 438 4778 Building 11 Ligocka St. 103, E: sales.is sgxsensortech.com 40-568 Katowice, www.sgxsensortech.com Poland VQ548MP Datasheet MEMs Catalytic Combustible Gas Sensor (4-Series) This datasheet describes the use of the VQ548MP 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 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, 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 The compensator is made in the same way as a detector Small size (16 x 20 mm) device except that instead of incorporating a catalyst in the Compatible with instruments using VQ500 type sensor coating layer, the device is treated so that oxidation cannot High resistance to mechanical shocks take place. Assessed as intrinsically safe The two devices are then used in a circuit that detects the Low orientation effect difference in their resistances. Since the two devices are ATEX Certified generally a different colour, they have different emissivity and hence different slope resistances. Therefore, to obtain the IECEx certified best temperature performance, it is necessary on occasion to UL Recognised - File E186043 connect a fixed resistor in parallel with the compensator to correct for its higher slope resistance. TECHNICAL SPECIFICATION Mechanical Dimensions see outline, page 4 OPERATING PRINCIPLE Body material PEI Weight 8g The silicon pellistor structure consists of a pair of accurately micro machined diaphragms with two embedded planar Environmental heater meanders coated with a layer incorporating a noble metal catalyst for the detector device and with inert layer for Ambient temperature range the compensator device. for operation / storage: 40 to +60 C certified: 40 to +75 C The meander acts both as an electrical heater and as a Operational pressure range 70 to 130 kPa resistance thermometer. The device is mounted on a PCB Humidity range for operation 0 to 95% with wire bonding and is surrounded by a plastic can with the and storage (non-condensing) end open to the atmosphere. If a flammable gas is present Gases Detected Most flammable gases when the device is heated to about 400 500 C, the gas will oxidise and the resultant release of energy will heat the and vapours device still further. This increase in temperature is detected as an increase in resistance of the meander. The temperature of Electrical the meander is also affected by ambient temperature and by DC supply to detectors +2.9 to +3.1V variations in thermal conductivity of the air caused by the Typical power 39 to 47mA possible presence of inert gases such as carbon dioxide. To (<96mA at power on) compensate for temperature changes not caused by the Mode of Operation Continuous oxidation of the flammable gas a second, inert device is used. Whilst SGX 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 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 SGX products in accordance with information contained herein. In case of modification of the product, SGX disclaims all liability. SGX Europe sp .z o.o. Poland REGON: 362332227 DS-0140, Issue 6, 03-May-2016, Page 1 SGX Europe Sp. Z o.o. T: +48 (0) 32 438 4778 Building 11 Ligocka St. 103, E: sales.is sgxsensortech.com 40-568 Katowice, www.sgxsensortech.com Poland PERFORMANCE NOTES 1. The polarity of the supply voltage may be reversed Minimum sensitivity 12 mV/% methane (measured with 1% methane at 3.0 0.1V) without harm. The only effect is to reverse the polarity of the output signal. Zero offset range in clean air 20 mV 2. Maximum (slowest) response time measured at 3.0 0.1 V using 1% methane in an SGX test manifold. Response Time (T ) 90 < 12 sec Faster response times will be achieved in (See Note 2) instruments/detectors with optimised gas delivery. Maximum gas concentration 5% methane in air 3. Exceeding these limits may degrade the stability of (see note 3) sensitivity or zero offset. The calibration of the sensor Long Term Zero drift < 1.0 mV / month should be checked if it has been exposed, whilst (see note 4) operating, to gas concentrations greater than the Long Term Sensitivity drift Lower Explosive Limit. < 0.6 mV / month (see note 5) 4. Over 90 day period. 5. Measured at 3.0 0.1V using 1% methane, over 90 days period. MAXIMUM RATINGS (Absolute values) Input voltages between pins: IMPORTANT PRECAUTIONS Pins 2 and 3 3.2 V Read the following instructions carefully before using the VQ548MP to avoid erroneous readings and to prevent the Pins 1 and 2 1.6 V device from permanent damage. Pins 1 and 3 1.6 V Heater voltages above the specified maximum rating can damage the MEMS Pellistor. Some compounds are known to affect the catalytic OPERATION reaction of coating material used in pellistors. It is recommended that the detector and compensator be Exposure to silicones (by far the most common & run in a Wheatstone bridge circuit. virulent poison), high levels of hydrogen sulfide (and other sulfur containing compounds), A suitable circuit is shown below. In use, the bridge supply phosphates and phosphorous containing voltage should be stable to within + 0.05 V, or the output in substances or lead containing compounds (e.g. clean air may change in sympathy. Although it is generally tetraethyl lead) will irreversibly poison the sensor. recommended that pellistors should be run with a constant High concentrations of flammable gas may also voltage supply to the bridge, it is possible to use a constant permanently affect the sensor response. current supply provided that the voltage across the bridge Lower concentrations of hydrogen sulfide and other in clean air remains within the recommended limits. compounds can cause a temporary loss in Recommended circuit diagram response. This is known as inhibition. Halogenated hydrocarbons such as Freons, trichloroethylene, and methyl chloride are also possible inhibitors. Sensors generally recover most of their original response once they are returned to fresh air. Specific protection may be needed in applications where poisons or inhibitors are continuously present. SGX recommends using ESD protection equipment when handling the sensor. Under no circumstances should the sensor pins be soldered directly to a PCB or wires. Excessive heat could cause irreparable damage to sensor. Information on the recommended sockets can be found on our website under the Frequently Asked Questions (FAQ) section. Please contact SGX Sensortech for any additional information. SGX Sensortech 2016 Document subject to disclaimer on page 1 DS-0140, Issue 6, 03-May-2016, Page 2