VQ25 Combustible Gas Detector Elements To be read in conjunction withIntroduction to Pellistor Gas Mechanical Sensor and Pellistor Application Notes 1, 2, 3, 4, 6 and 7. Mounting see page 3 Outline . see page 2 INTRODUCTION TheVQ25consistsoftwomatchedelementswhichareusedfor MARKING the detection of combustible gases in air. They are not Each element is identified by a unique serial number written on generally suitable forthedetectionof methane inair. the can of both the detector and compensator. The serial Theelementsaredesignedespeciallyforuseinsituationswhere number is written in red on the detector and black on the they are liable to be exposed to high concentrations of compensator. In addition, the detector carries a red circular flammable gas, up to 100%. The VQ25 remains substantially label on the base identifying the device type. unchanged, even after long periods of exposure to high concentrations, although it is advisable to check the zero NOTES calibration after each such exposure. The VQ25 is also useful for the detection of combustible 1. Operation may be under either direct flow or diffusion conditions in appropriate mountings (see page 3). vapours containing halogens, or when small amounts of non- flammable halogenated hydrocarbons are present. 2. With open-circuit conditions at the bridge output. There is no interference from water vapour or carbon dioxide 3. The response time is a function of the type of mounting unless the concentrations are high enough to affect the used. flammability of the gas mixture. Using the recommended 4. Theelementsaresupplied asamatchedpairwithatrimming bridge circuit below and the mounting arrangement shown on resistor R of the correct value which is between 39 and page 3, the minimum sensitivity is 25 mV/1% n-butane. 120O. The trimming resistor is to be connected across the compensator element as shown below. GENERAL DATA Electrical The information given below relates to the VQ25 operating in the recommended circuit shown. Operation (see note 1) . continuous Bridge supply . 2.0+ 0.1 V Bridge power consumption . 0.75 W max Minimum sensitivity (see note 2) 25 mV/1% n-butane Linearity linear up to 1.5% n-butane Response time to register 0.5% in a 1% concentration (see notes 2 and 3) 3 seconds BRIDGE CIRCUIT COMPENSATOR 4915A (BLACK SLEEVE) SEE R NOTE 4 27O 1 kO 2 V ZERO SET 27O DETECTOR (RED SLEEVE) OUTPUT A1A-VQ25 Issue 5, March 2007 SGX Sensortech(IS) Ltd. Registered in England No.08067077TYPICAL VARIATIONOF BRIDGE OUTPUT WITH SUPPLY VOLTAGE 6075A 20 METHANE GAS CONCENTRATION 20% LEL 15 HEXANE 10 HEPTANE CYCLOHEXANE BUTANE OCTANE 5 0 0 0.5 1.0 1.5 2.0 2.5 3.0 BRIDGE SUPPLY VOLTAGE (V) OUTLINE (All dimensions without limits arenominal) 2311B Ref Millimetres F D E A 11.05+ 0.25 1B B 6.10+ 0.25 C C 3.56+ 0.13 D 63.50 min E 1.02 1G 1A F 7.37+ 0.51 G 8.20 max H 9.53 J 1.52 J O-RING METAL INSULATOR FLANGE H SEE NOTE Note No bends may be made in this length. A1A-VQ25 Issue 5, March 2007 SGX Sensortech(IS) Ltd. Registered in England No.08067077 BRIDGE OUTPUT (mV)