VQ23TB

VQ23TB Combustible Gas Detector Elements MARKING To be read in conjunction with "Introduction to Pellistor Gas Sensors" 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 number is written in red on the detector and black on the compensator. In addition, the detector carries a red circular label on the base identifying the device type. INTRODUCTION The VQ23TB is an improved poison-resistant sensor consisting 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 from water vapour or carbon dioxide. Using the recommended bridge circuit below and the mounting arrangement shown on page 3, the minimum sensitivity is 15 mV/% methane. The VQ23TB has been designed for use in atmospheres where traces of silicone and other poisoning agents may be present. NOTES 1. Operation may be under either direct flow or diffusion conditions in appropriate mountings (see page 3). 2. With open-circuit conditions at the bridge output. 3. The response time is a function of the type of mounting used. 4. If the VQ23TB is exposed to greater than 5% methane concentration, the calibration of the instrument should be checked. 5. The elements are supplied as a matched pair with a trimming resistor R of the correct value which is supplied where necessary. The trimming resistor is to be connected across the compensator element as shown below. 6. The resistance to poisoning by silicone compounds is partly dependent upon the type of housing within which the elements are mounted. The results shown on page 2 were obtained using a flow housing shown on page 3. 7. The response to certain of the heavy flammable vapours especially aromatic substances with side chains, may be lower than that calculated from the conversion (K) factors listed in the preamble. GENERAL DATA Electrical The information given below relates to the VQ23TB operating in the recommended circuit shown. Operation (see note 1) . . . . . . . . . continuous Bridge supply . . . . . . . . . . . 2.4V to 2.6V Bridge power consumption . . . . . . . 1.1 W max Typical average sensor current . . . . . . . . 335 mA Minimum sensitivity (see note 2) . . . 15 mV/% methane Linearity . . . . . . . . . linear up to 5% methane Response time to register 1 1/4% in a 2 1/2% concentration (see notes 2 and 3) . . . . 2 seconds Maximum methane concentration (see note 4) . . . . . . . . . . . . . 5 % Mechanical Mounting . . . . . . . . . . . . . . see page 3 Outline . . . . . . . . . . . . . . . see page 2 BRIDGE CIRCUIT COMPENSATOR (BLACK SLEEVE) 3608B R 27O 2.5 V SEE NOTE 5 1kO ZERO SET 27O DETECTOR (RED SLEEVE) OUTPUT SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ23TB Issue 1,15 June 2015 TYPICAL RESPONSE OF VQ23TB AND STANDARD PELLISTOR WHEN EXPOSED TO HEXAMETHYL DISILOXANE ATMOSPHERES 5521A PERCENTAGE OF INITIAL SENSITIVITY TO 1% METHANE IN AIR 100 5ppm 10ppm 50 0 0 5 10 15 20 25 30 35 40 45 50 HOURS PERCENTAGE OF INITIAL SENSITIVITY TO 1% METHANE IN AIR 100 50ppm 100ppm 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 A C B 1A 1G C INSULATOR Millimetres Inches 11.3 max 10.8 min 6.35 max 5.85 min 3.69 max 3.43 min 40.0 min 1.0 nom 7.88 max 6.86 min 8.2 max 1.5 nom 0.445 max 0.425 min 0.250 max 0.230 min 0.145 max 0.135 min 1.575 min 0.039 nom 0.310 max 0.270 min 0.323 max 0.059 nom E 1B METAL FLANGE H O-RING D E F G H Inch dimensions have been derived from millimetres. SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ23TB Issue 1,15 June 2015 RECOMMENDED MOUNTING ARRANGEMENTS 2310C AA LEAKPROOF JOINT AB 60 MESH STAINLESS STEEL GAUZE 1A D Ref Millimetres AA AB AC AD AE AF AG 19.05 max 9.53 + 0.13 8.33 + 0.13 8.20 min 19.05 max 9.53 + 0.13 8.20 min AC FLOW RATE 500 cm3/min AE AF FILTER PAPER AND 60 MESH STAINLESS STEEL GAUZE 1AG SGX Sensortech(IS) Ltd Registered in England No.08067077 A1A-VQ23TB Issue 1,15 June 2015