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
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