Revised 08/03
2
APPLICATION NOTES FOR TGS2611
To facilitate ease in manufacturing gas detectors,
both Figaro TGS2611-J00 and TGS2611-B00
methane gas sensors are individually marked with
an ID number (
see Figure 1
) indicating a factory
presorted classification which corresponds to
narrow ranges of sensor resistance in methane.
When the sensor’s ID number is properly used,
the calibration process can be greatly simplified,
eliminating long preconditioning time and the
complicated handling of calibration gas.
1. Detector Circuit Design
1-1
Basic circuit with temperature compensation
Figure 2 shows an example of a basic circuit for
gas detection, including temperature compen-
sation for variations caused by ambient
temperature fluctuations. Typical values for the
circuit components are as follows:
R
L
: refer to Table 1
R
TH
: 4.7k
Ω
(
±
3%), B=3977 (
±
5%)
R
A
: 11.5k
Ω
(
±
1%)
R
B
: 4.32k
Ω
(
±
1%)
R
C
: 8.25k
Ω
(
±
1%)
The values for components related to
temperature compensation should be chosen so
that Vref is one-half of the Vc value at standard
temperature (20˚C). The Vref curve should
approximate the temperature dependency curve
of the V
RL
when compensation is properly done.
1-2
Selecting a load resistor (R
L
)
To optimize resolution of the output signal at
the desired alarming concentration, it is neces-
sary to adjust the resistance of the load resistor
(R
L
). It is recommended that R
L
be selected at a
value which is equal to the sensor’s resistance
(Rs) at the alarming concentration (i.e. Rs/R
L
=
1.0). Please refer to the brochure “
General
Information for TGS Sensors
” for more details.
Since the ID number corresponding to sensor
resistance in methane gas is indicated on the
sensor cap, the load resistor value can be selected
according to Table 1. For example, for an alarm
setting at 10% LEL, when using a sensor having
an ID number of 7, the R
L
value should be set at
1.27k
Ω
. By using the recommended R
L
, the V
RL
value at the alarming point typically will be 2.5V,
which is equal to half of the circuit voltage (Vc).
Fig. 1 - Sensor markings
Fig. 2 - Basic circuit with
temperature compensation
78M05
R
L
R
A
Alarm signal
(Active = 'L')
D.C. input
+
-
V
REF
Vc = 5.0
±
0.2V
V
RL
R
B
R
C
R
TH
Comparator
GND
4
1
3
2
Voltage
regulator
TGS
2611
Table 1 - Recommended R
L
by sensor ID
Note:
Lower explosion limit (LEL) of methane = 50,000ppm
r
o
s
n
e
S
#
D
I
R
L
k
(
Ω
h
t
i
w
)
±
e
c
n
a
r
e
l
o
t
%
1
L
E
L
%
5
L
E
L
%
0
1
L
E
L
%
5
1
L
E
L
%
0
2
1
0
6
7
9
.
0
5
1
7
.
0
0
9
5
.
0
1
1
5
.
0
2
0
7
0
.
1
7
8
7
.
0
9
4
6
.
0
2
6
5
.
0
3
0
8
1
.
1
6
6
8
.
0
5
1
7
.
0
9
1
6
.
0
4
0
0
3
.
1
3
5
9
.
0
7
8
7
.
0
1
8
6
.
0
5
0
3
4
.
1
5
0
.
1
6
6
8
.
0
0
5
7
.
0
6
0
8
5
.
1
5
1
.
1
3
5
9
.
0
5
2
8
.
0
7
0
4
7
.
1
7
2
.
1
5
0
.
1
9
0
9
.
0
8
0
1
9
.
1
0
4
.
1
5
1
.
1
0
0
.
1
9
0
0
1
.
2
4
5
.
1
7
2
.
1
0
1
.
1
0
1
2
3
.
2
9
6
.
1
0
4
.
1
1
2
.
1
1
1
5
5
.
2
7
8
.
1
4
5
.
1
3
3
.
1
2
1
0
8
.
2
5
0
.
2
9
6
.
1
7
4
.
1
3
1
9
0
.
3
6
2
.
2
7
8
.
1
2
6
.
1
4
1
0
4
.
3
9
4
.
2
5
0
.
2
8
7
.
1
5
1
4
7
.
3
4
7
.
2
6
2
.
2
6
9
.
1
6
1
2
1
.
4
1
0
.
3
9
4
.
2
5
1
.
2
7
1
3
5
.
4
2
3
.
3
4
7
.
2
7
3
.
2
8
1
9
9
.
4
5
6
.
3
1
0
.
3
1
6
.
2
9
1
9
4
.
5
2
0
.
4
2
3
.
3
7
8
.
2
0
2
4
0
.
6
2
4
.
4
5
6
.
3
6
1
.
3
1
2
5
6
.
6
7
8
.
4
2
0
.
4
8
4
.
3
2
2
2
3
.
7
6
3
.
5
2
4
.
4
3
8
.
3
3
2
6
0
.
8
0
9
.
5
7
8
.
4
2
2
.
4
4
2
7
8
.
8
9
4
.
6
6
3
.
5
4
6
.
4
Sensor
code
Lot #
ID #
TGS2611
984AA #07
TGS2611
314AE #07
TGS2611-J00
TGS2611-B00
