VQ35MB Amphenol

VQ35 Series Thermal Conductivity Gas Detector Elements To be read in conjunction withIntroduction to Pellistor Gas BRIDGE CIRCUIT Sensor and Pellistor Application Note 5 Thermal REFERENCE 6821A Conductivity Sensors. ELEMENT INTRODUCTION 27O The VQ35 series devices consist of two matched elements 1kO which are used for the detection of gases in 0 100% by 4.25 V ZERO SET volume concentrations using the recommended bridge circuit (see below) and the mounting arrangement shown on page 3. 27O TheVQ35MissuppliedwithbraidedleadsandtheVQ35MBhas extended pins for fitting directly to printed circuit boards. The elements operate on the thermal conductivity principle. SENSING The sensing element is open to the atmosphere under test and ELEMENT the reference element is supplied sealed in reference air. The response of the devices is dependent upon the difference OUTPUT between the thermal conductivity of the atmosphere under test and the reference air. When the atmosphere under test has athermalconductivityhigherthanthereferenceair,thesensing element loses more heat to the surroundings than the reference MARKING element. This increased heat loss causes a cooling of the Each element is identified by a unique serial number written on sensing element and a subsequent reduction in the resistance the can of both the sensing and reference elements. The serial of the sensing element compared to the reference element. number is written in red on the sensing element and black on The thermal conductivity of a gas mixture is dependent on the reference element. In addition, the sensing element carries temperature and the individual thermal conductivity of the a red circular label on the base identifying the device type. constituents of the mixture. The temperature of importance is the operating temperature of the sensing element (typically a NOTES maximum of 500 8C at the recommended bridge supply 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 3). 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 3. The response time is a function of the type of mounting some of the more common gases relative to air is tabulated on used. page 2 at various temperatures. Note that when operating the sensor in a constant voltage mode the response will ORDERING INFORMATION be non-linear to increasing concentrations of a gas. Order Code Description GENERAL DATA VQ35 Flexi-leg sensor with open compensator can. Electrical This device needs to have the compensator mounted inasealed chamberfilledwith airor The information given below relates to the VQ35 series nitrogen. operating in the recommended circuit shown. Operation (see note 1) ......... continuous VQ35B PCB legged sensor with open compensator Bridge supply ........... 4.25 V can. This device needs to have the Bridge power consumption ....... 0.26 W max compensator mounted in a sealed chamber Response to methane in air (see note 2) . . 1.0 mV/% min filled with air or nitrogen. Response time ............ see note 3 VQ35M Flexi-leg sensor with sealed compensator can. Mechanical Mounting.............. see page 3 VQ35MB PCB legged sensor with sealed compensator Outlines .............. see page 2 can. SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ35 Ser Issue 6, March 2007THERMAL 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 OUTLINE OF VQ35M (All dimensions without limits are nominal) 2311B D F Ref Millimetres E 1B A 11.05+ 0.25 B 6.10+ 0.25 C C 3.56+ 0.13 D 63.5 min E 1.0 1G 1A F* G 8.2 max H 9.53 J O-RING J 1.5 INSULATOR METAL FLANGE * sensing element 6.25+ 0.50 H SEE NOTE reference element 7.75+ 0.38 Note No bends may be made in this length. OUTLINE OF VQ35MB (All dimensions without limits are nominal) 7218 F D Ref Millimetres E 1B A 11.05+ 0.25 B 6.10+ 0.25 C C 3.56+ 0.13 D 40.0 min E 1.0 1A 1G F* G 8.2 max H 1.5 H O-RING INSULATOR METAL * sensing element 6.25+ 0.50 FLANGE reference element 7.75+ 0.38 SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ35 Ser Issue 6, March 2007