VQ22

Combustible Gas Detector Elements

1kO

ZERO SET

27O

OUTPUT

COMPENSATOR

(BLACK SLEEVE)

DETECTOR

(RED SLEEVE)

2309C

SEE

NOTE 5

To be read in conjunction with "Introduction to Pellistor Gas

Sensors" and Pellistor Application Notes 1, 2, 3, 4, 6 and 7.

INTRODUCTION

The VQ22 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 10 mV/% methane.

The VQ22 has been designed for use in atmospheres where

traces of silicone and other poisoning agents may be present.

GENERAL DATA

Electrical

The information given below relates to the VQ22 operating in

the recommended circuit shown.

Operation (see note 1) .........continuous

Bridge supply ...........2.0+ 0.1 V

Bridge power consumption .......0.48 W max

Typical average sensor current ..... 175 mA

Minimum sensitivity (see note 2) . . . 10 mV/% methane

Linearity ......... linear up to 5% methane

Response time to register 1

%ina2

concentration (see notes 2 and 3) ....2 seconds

Maximum methane concentration

(see note 4) ...........5 %

Mechanical

Mounting ..............seepage 3

Outline ...............seepage 2

BRIDGE CIRCUIT

MARKING

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.

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 VQ22 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.

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.

SGX Sensortech(IS) Ltd Registered in England No.08067077

A1A-VQ22 Issue 5, March 2007

100

5519A

1.0 1.4

1.8

2.2

2.6 3.0

RELATIVE RESPONSE TO METHANE (%)

BRIDGE SUPPLY VOLTAGE (V)

Methane

Propane

n-Hexane

n-Octane

TYPICAL RESPONSE OF VQ22 TO 20% L.E.L. OF VARIOUS GASES AND VAPOURS

(RELATIVE TO METHANE) AS THE BRIDGE SUPPLY VOLTAGE IS VARIED

OUTLINE (All dimensions without limits are nominal)

Ref Millimetres

A 11.05 + 0.25

B 6.10 + 0.25

C 3.56 + 0.13

D 63.50 min

E 1.02

F 7.37 + 0.51

G 8.20 max

H 9.53

J 1.52

Note No bends may be made in this length.

INSULATOR

METAL

FLANGE

SEE NOTE

J O-RING

2311B

SGX Sensortech(IS) Ltd Registered in England No.08067077

A1A-VQ22 Issue 5, March 2007