VQ21 Combustible Gas Detector Elements To be read in conjunction withIntroduction to Pellistor Gas MARKING Sensor and Pellistor Application Notes 1, 2, 3, 4, 6 and 7. Each element is identified by a unique serial number written on the can of both the detector and compensator. The serial INTRODUCTION number is written in red on the detector and black on the The VQ21 is an improved poison-resistant sensor consisting of compensator. In addition, the detector carries a red circular two matched elements which are used for the detection of label on the base identifying the device type. combustible gases, particularly methane in air mixtures in concentrations from 0.1% upwards. There is no interference NOTES from water vapour or carbon dioxide. Using the recommended 1. Operation may be under either direct flow or diffusion bridge circuit below and the mounting arrangement shown on conditions in appropriate mountings (see page 3). page 3, the minimum sensitivity is 10 mV/% methane. 2. With open-circuit conditions at the bridge output. The VQ21 has been designed for use in atmospheres where 3. The response time is a function of the type of mounting traces of silicone and other poisoning agents may be present. used. 4. If the VQ21 is exposed to greater than 5% methane GENERALDATA concentration, the calibration of the instrument should be Electrical checked. The information given below relates to the VQ21 operating in 5. The elements are supplied as a matched pair with a the recommended circuit shown. trimming resistor R of the correct value which is supplied Operation (see note 1) ......... continuous where necessary. The trimming resistor is to be connected Bridge supply ........... 2.0+ 0.1 V across the compensator element as shown below. Bridge power consumption ....... 0.75 W max 6. The resistance to poisoning by silicone compounds is partly Typical average sensor current..... 300 mA dependent upon the type of housing within which the Minimum sensitivity (see note 2) . 10 mV/% methane elements are mounted. The results shown on page 2 were Linearity ......... linear up to 5% methane obtained using a flow housing shown on page 3. 1 1 Response time to register 1 /%ina2 / % 4 2 7. The response to certain of the heavy flammable vapours, concentration (see notes 2 and 3) .... 2 seconds especially aromatic substances with side chains, may be Maximum methane concentration lower than that calculated from the conversion (K) factors (see note 4) ........... 5 % listed in the preamble. Mechanical Mounting.............. see page 3 Outline............... see page 3 BRIDGECIRCUIT COMPENSATOR 2309C (BLACK SLEEVE) SEE R NOTE 5 27O 1kO 2V ZERO SET 27O DETECTOR (RED SLEEVE) OUTPUT SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ21 Issue 4, March 2007TYPICALRESPONSEOFVQ21,STANDARDPELLISTOR ANDVQ16WHENEXPOSED TO HEXAMETHYLDISILOXANE ATMOSPHERES 5430A PERCENTAGE OF INITIAL SENSITIVITY TO 1% METHANE IN AIR 100 5 P.P.M. 10 P.P.M. 50 0 0 5 10 15 20 25 30 35 40 50 45 HOURS PERCENTAGE OF INITIAL SENSITIVITY TO 1% METHANE IN AIR 100 25 P.P.M. 50 P.P.M. 100 P.P.M. 50 STANDARD VQ16 PELLISTOR 5 P.P.M. 0 0 50 100 150 200 250 300 350 400 450 500 550 600 MINUTES TYPICALRESPONSEOFVQ21TO20%LELOFVARIOUSGASESANDVAPOURS (RELATIVE TOMETHANE)ASTHEBRIDGE SUPPLYVOLTAGEISVARIED 100 5518A 80 Methane 60 40 Propane 20 n-Hexane n-Octane 0 1.0 1.4 1.8 2.2 2.6 3.0 BRIDGE SUPPLY VOLTAGE (V) SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ21 Issue 4, March 2007 RELATIVE RESPONSE TO METHANE (%)