VQ3 Series Combustible Gas Detector Elements To be read in conjunction withIntroduction to Pellistor Gas NOTES Sensor and Pellistor Application Notes 1, 2, 3, 4, 6 and 7. 1. Further details of the linearity of pellistor-based gas sensors may be found in SGX Sensortech Pellistor Application INTRODUCTION Note 4,Linearity corrections to Pellistor responses at The VQ3 is a catalytic flammable gas sensor (also called a high gas level. pellistor) which consists of two matched elements. It may be 2. If the VQ3 is exposed to greater than 100% LEL used for the detection of a wide variety of combustible gases in concentration of a flammable gas whist operating, the air, at concentrations between 0% and 100% of the Lower calibration of the instrument should be checked. Explosive Limit (LEL) of a given flammable gas. The principles 3. Some flammable gases and vapours, in particular silicones, of operation of pellistor-type gas sensors are described in the some fuel additives and some sulphur-bearing compounds, SGX Sensortech Gas Sensors brochure. The VQ3, in can damage or poison pellistors. The long-term drift data particular, is a very well established sensor for general purpose expressed above assumes that the sensor is not exposed to use in fixed gas detection systems where low cost and chemicals known to poison them. For more guidance, stability are the primary considerations. A wide range of other please refer to SGX Sensortech Pellistor Application pellistor type gas sensors is available from SGX Sensortech. Note 6,Pellistor Poisonin. 4. Thechoiceof 1kO asthevalue forthebalancing resistorsin GENERAL CHARACTERISTICS the bridge circuit shown in Fig. 1 is arbitrary, and assumes The information given below relates to the VQ3 operating in the that the measuring device imposes a high impedance load recommended circuit shown in Fig. 1. The instrument designer across the signal terminals. The use of a measuring device should always be aware that the mounting arrangement and imposing a lower impedance load across the output stage circuitry employed within an instrument design will often (for example a moving coil voltmeter), may require a lower profoundly modify the performance of any gas sensor. value of balancing resistor to be fitted. Operation.......... suitable for continuous 5. The elements are supplied as a matched pair, complete with or intermittent operation a trimming resistor of the correct value which is not less Bridge supply ........... 2.5+ 0.1 V than 39 O. The trimming resistor should be connected Typical bridge current........... 330mA across the compensator element as shown in Fig. 1. Minimum sensitivity ....... 21 mV/% methane Linearity (see note 1) .... linear within 5% of reading OPTIONS AVAILABLE up to 60% LEL (methane) VQ3 Standard device, with stranded flexible leads. Repeatability.......... 2%LEL (methane) Response time VQ3AA Optimised for use with constant current circuitry (T , measured at 50%LEL methane).... 2 seconds operating at 300 mA. 50 Maximum methane concentration (see note 2) . 10% VQ3B Supplied with pcb compatible leads. Typical long term drift (see note 3): VQ3BJ As VQ3B but supplied with size 1206 chip resistor zero............. 0.5 mV/month instead of the standard wire ended resistor. span............ 2% signal/month Outline............... see page 2 WARNING Shock test ....... 250g,5 blows in each plane Vibration test.... 20g,24 cycles from 100 to 3200 Hz To ensure safe operation, to satisfy regulatory bodies and to comply with the requirements of approval authorities, SGX Sensortech recommends that a suitable flame MARKING arrestor be used with the device. The active (detector) device may be identified by the bead itself being dark in colour and it has a red serial number written on its metal can. The compensators bead is white and carries a black serial number written on its metal can. SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ3 Ser Issue 6, March 20077828 COMPENSATOR (BLACK NUMBER) SEE R NOTE 5 1kO SEE NOTE 4 50 kO 2.5 V ZERO SET 1kO SEE NOTE 4 DETECTOR (RED NUMBER) OUTPUT Fig. 1 Bridge Circuit OUTLINE OF VQ3 AND VQ3AA (All dimensionswithout limits are nominal) 2311C F D Ref Millimetres Inches E 1B A 11.05+ 0.25 0.435+ 0.010 C B 6.10+ 0.25 0.240+ 0.010 C 3.56+ 0.13 0.140+ 0.005 D 63.5 min 2.500 min 1A 1G E 1.0 0.039 F 5.84+ 0.51 0.230+ 0.020 G 8.20 max 0.323 max SEE NOTE 1 H 9.53 0.375 JO-RING METAL J 1.5 0.059 INSULATOR FLANGE H Inch dimensions have been derived from millimetres. SEE NOTE 2 Outline Notes 1. The wire comprises 13 strands, each 0.2 mm across. 2. No bends may be made in this length. OUTLINE OF VQ3B AND VQ3BJ (All dimensionswithout limits are nominal) 7218A F D Ref Millimetres Inches E 1B A 11.05+ 0.25 0.435+ 0.010 C B 6.10+ 0.25 0.240+ 0.010 C 3.56+ 0.13 0.140+ 0.005 D 40.0 1.575 1A 1G E 1.0 0.039 F 5.84+ 0.51 0.230+ 0.020 G 8.20 max 0.323 max SEE NOTE H 1.5 0.059 H O-RING METAL INSULATOR FLANGE Inch dimensions have been derived from millimetres. Outline Note The wire comprises a single strand, 0.5 mm across. SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ3 Ser Issue 6, March 2007