VQ31MB Amphenol

VQ31 Series Thermal Conductivity Gas Detector Elements To be read in conjunction withIntroduction to Pellistor Gas BRIDGE CIRCUIT Sensor and Pellistor Application Note 5 Thermal Conductivity Sensors. REFERENCE 4688B ELEMENT INTRODUCTION The VQ31 series devices consist of two matched elements 27O which are used for the detection of gases in 0 100% by 1kO volume concentrations using the recommended bridge circuit 2V ZERO SET (see below) and the mounting arrangement shown on page 4. 27O TheVQ31Missuppliedwithbraided leadsandtheVQ31MBhas extended pins for fitting directly to printed circuit boards. The elements operate on the thermal conductivity principle. The sensing element is open to the atmosphere under test and SENSING ELEMENT the reference element is supplied sealed in reference air. The response of the devices is dependent upon the difference between the thermal conductivity of the atmosphere under OUTPUT test and the reference air. When the atmosphere under test has athermalconductivityhigherthanthereferenceair,thesensing element loses more heat to the surroundings than the reference element. This increased heat loss causes a cooling of the MARKING sensing element and a subsequent reduction in the resistance Each element is identified by a unique serial number written on of the sensing element compared to the reference element. the can of both the sensing and reference elements. The serial The thermal conductivity of a gas mixture is dependent on number is written in red on the sensing element and black on temperature and the individual thermal conductivity of the the reference element. In addition, the sensing element carries constituents of the mixture. The temperature of importance is a red circular label on the base identifying the device type. the operating temperature of the sensing element (typically a maximum of 500 8C at the recommended bridge supply NOTES voltage). The sensor can be operated at any bridge voltage up 1. Operation may be under either direct flow or diffusion to and including the recommended bridge supply, with the conditions in appropriate mountings (see page 4). sensing element therefore running at temperatures up to and 2. With open-circuit conditions at the bridge output. including the typical maximum. The thermal conductivity of some of the more common gases relative to air is tabulated on 3. The response time is a function of the type of mounting page 2 at various temperatures. Note that when operating used. the sensor in a constant voltage mode the response will be non-linear to increasing concentrations of a gas. ORDERING INFORMATION GENERAL DATA Order Code Description Electrical VQ31 Flexi-leg sensor with open compensator can. The information given below relates to the VQ31 series This device needs to have the compensator operating in the recommended circuit shown. mounted in a sealed chamber filled with airor nitrogen. Operation (see note 1) ......... continuous Bridge supply ........... 2.0to3.5 V VQ31B PCB legged sensor with open compensator Bridge power consumption: can. This device needs to have the at3.5V............. 0.35 W max compensator mounted in a sealed chamber at2.0V............. 0.28 W filled with air or nitrogen. Typical response to methane in air (see note 2): VQ31M Flexi-leg sensor with sealed compensator at3.5V............. 2.5 mV/% can. at2.0V............. 1.0 mV/% Response time ............ see note 3 VQ31MB PCB legged sensor with sealed compensator can. Mechanical Mounting.............. see page 4 Outlines .............. see page 3 Shock test ....... 250g,5 blows in each plane Vibration test.... 20g,24 cycles from 100 to 3200 Hz SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ31 Ser Issue 6, March 2007300 THERMAL CONDUCTIVITY OF GASES (Relative to air) Element temperature 08C 1008C 2008C 3008C 4008C 5008C 6008C Air 1.000 1.000 1.000 1.000 1.000 1.000 1.000 Nitrogen 0.996 0.993 0.997 0.999 0.998 0.994 0.988 Oxygen 0.987 1.026 1.049 1.062 1.065 1.062 1.056 Argon 0.686 0.687 0.682 0.674 0.663 0.650 0.636 Carbon dioxide 0.621 0.745 0.832 0.893 0.933 0.959 0.975 Water vapour 0.969 1.076 1.192 1.303 1.404 1.493 1.574 Methane 1.244 1.500 1.723 1.911 2.066 2.192 2.296 Ethane 0.742 1.027 1.271 1.474 1.638 1.769 1.874 Propane 0.619 0.874 1.092 1.271 1.415 1.529 1.619 Carbon monoxide 0.961 0.962 0.970 0.975 0.976 0.974 0.970 Ethylene 0.703 0.970 1.195 1.378 1.524 1.637 1.727 Acetylene 0.886 1.040 1.155 1.240 1.301 1.344 1.376 Hydrogen 7.371 6.918 6.692 6.548 6.435 6.336 6.252 Helium 5.972 5.681 5.492 5.338 5.197 5.062 4.939 Ammonia 1.082 1.295 1.493 1.670 1.824 1.955 2.069 TYPICAL BRIDGE OUTPUT FOR METHANE-IN-AIR MIXTURES 6590A 3.5 V INPUT 100 2 V INPUT 0 0 20 406080 100 METHANE CONCENTRATION (% VOLUME) SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ31 Ser Issue 6, March 2007 200 OUTPUT VOLTAGE (mV)