VQ23TB 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 VQ23TB is an improved poison-resistant sensor consisting compensator. In addition, the detector carries a red circular label on the base identifying the device type. of two matched elements which are used for the detection of 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 15 mV/% methane. 2. With open-circuit conditions at the bridge output. The VQ23TB has been designed for use in atmospheres 3. The response time is a function of the type of mounting where traces of silicone and other poisoning agents may be used. present. 4. If the VQ23TB is exposed to greater than 5% methane concentration, the calibration of the instrument should be GENERAL DATA checked. Electrical 5. The elements are supplied as a matched pair with a The information given below relates to the VQ23 TB trimming resistor R of the correct value which is supplied operating in the recommended circuit shown. where necessary. The trimming resistor is to be connected Operation (see note 1) . continuous across the compensator element as shown below. Bridge supply . 2.4V to 2.6V 6. The resistance to poisoning by silicone compounds is partly Bridge power consumption . 1.1 W max dependent upon the type of housing within which the Typical average sensor current 335 mA elements are mounted. The results shown on page 2 were Minimum sensitivity (see note 2) . 15 mV/% methane obtained using a flow housing shown on page 3. Linearity . linear up to 5% methane 7. The response to certain of the heavy flammable vapours 1 1 Response time to register 1 / % in a 2 / % 4 2 especially aromatic substances with side chains, may be concentration (see notes 2 and 3) 2 seconds lower than that calculated from the conversion (K) factors Maximum methane concentration listed in the preamble. (see note 4) . 5 % Mechanical Mounting see page 3 Outline . see page 2 BRIDGE CIRCUIT COMPENSATOR 3608B (BLACK SLEEVE) SEE R NOTE 5 27O 1kO ZERO 2.5 V SET 27O DETECTOR (RED SLEEVE) OUTPUT SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ23TB Issue 1,15 June 2015TYPICAL RESPONSE OF VQ23TB AND STANDARD PELLISTOR WHEN EXPOSED TO HEXAMETHYL DISILOXANE ATMOSPHERES 5521A PERCENTAGE OF INITIAL SENSITIVITY TO 1% METHANE IN AIR 100 5ppm 10 ppm 50 0 0 5 10 15 20 25 30 35 40 45 50 HOURS PERCENTAGE OF INITIAL SENSITIVITY TO 1% METHANE IN AIR 100 50 ppm 100 ppm 50 STANDARD PELLISTOR 0 0 50 100 150 200 250 300 350 400 MINUTES OUTLINE (All dimensions without limits are nominal) 7218 F D Ref Millimetres Inches E 1B 11.3 max 0.445 max A C 10.8 min 0.425 min 6.35 max 0.250 max B 5.85 min 0.230 min 1A 1G 3.69 max 0.145 max C 3.43 min 0.135 min D 40.0 min 1.575 min E 1.0 nom 0.039 nom H O-RING METAL 7.88 max 0.310 max INSULATOR F FLANGE 6.86 min 0.270 min G 8.2 max 0.323 max H 1.5 nom 0.059 nom Inch dimensions have been derived from millimetres. SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ23TB Issue 1,15 June 2015