Figaro TGS2611 Application Notes
APPLICATION NOTES FOR TGS2611
Application Notes for Methane Gas Detectors using TGS2611
The TGS2611 methane gas sensor
has been presorted into
groupings which will allow users
to simplify the manufacturing
process for methane gas
detectors. This brochure offers
example application circuits and
important technical advice for
designing and manufacturing gas
detectors which use classified
TGS2611 sensors.
Page
an ISO9001 company
Introduction......................................................................................................2
Detector Circuit Design
Basic Circuit with T emperature Compensation............................................2
Selecting a Load Resistor .................................................................................2
Compensation for Internally Generated Heat..............................................3
Heater Breakage Detection Circuit.........................................................3
Sensor Malfunction Detection Circuit.........................................................3
Prevention of Intermittent Alarming..............................................................4
Alarm Prevention during W armup................................................................4
Alarm Delay Circuit..........................................................................5
Application Circuit...................................................................................5
Manufacturing Process
Handling and Storage of Sensors..........................................................5
L Selection...............................................................................................5
R
PCB Assembly....................................................................................5
Sensor Assembly..................................................................................5
Final Assembly.................................................................................................6
Preheating of Final Assembly.....................................................................6
Gas Test..............................................................................................6
Storage of Finished Products..........................................................................6
Anticipated Performance at 10%LEL of Methane...........................................................6
Pre-calibrated Sensor Module...........................................................................................7
Appendix...............................................................................................................8
See also Technical Brochure ‘Technical Information on Usage of TGS
Sensors for Toxic and Explosive Gas Leak Detectors’.
Revised 08/03
IMPORTANT NOTE: OPERATING CONDITIONS IN WHICH FIGARO SENSORS ARE USED
WILL VARY WITH EACH CUSTOMER’S SPECIFIC APPLICATIONS. FIGARO STRONGLY
RECOMMENDS CONSULTING OUR TECHNICAL STAFF BEFORE DEPLOYING FIGARO
SENSORS IN YOUR APPLICATION AND, IN PARTICULAR, WHEN CUSTOMER’S TARGET
GASES ARE NOT LISTED HEREIN. FIGARO CANNOT ASSUME ANY RESPONSIBILITY
FOR ANY USE OF ITS SENSORS IN A PRODUCT OR APPLICATION FOR WHICH SENSOR
HAS NOT BEEN SPECIFICALLY TESTED BY FIGARO.
TGS2611-J00 is a UL recognized component in accordance with the
requirements of UL2075. Please note that component recognition testing
has confirmed long term stability in 60ppm of methane; other characteristics
shown in this brochure have not been confirmed by UL as part of component
recognition.
1
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 compensation for variations caused by ambient
temperature fluctuations. Typical values for the
circuit components are as follows:
RL : refer to Table 1
R
TH : 4.7k
Ω (±
3%), B=3977 (±5%)
RA : 11.5kΩ (±1%)
RB : 4.32kΩ (±1%)
RC : 8.25kΩ (±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 VRL 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 necessary to adjust the resistance of the load resistor
(RL). It is recommended that RL be selected at a
value which is equal to the sensor’s resistance
(Rs) at the alarming concentration (i.e. Rs/RL =
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
1.27kΩ. By using the recommended RL, the VRL
value at the alarming point typically will be 2.5V,
which is equal to half of the circuit voltage (Vc).
Sensor
code
TGS2611
984AA
TGS2611-J00 TGS2611-B00
Fig. 1 - Sensor markings
Voltage
regulator
78M05
D.C. input
#DI
10679.0517.0095.0115.0
2070.1787.0946.0265.0
3081.1668.0517.0916.0
4003.1359.0787.0186.0
5034.150.1668.0057.0
6085.151.1359.0528.0
7047.172.150.1909.0
8019.104.151.100.1
9001.245.172.101.1
0123.296.104.112.1
1155.278.145.133.1
2108.250.296.174.1
3190.362.278.126.1
4104.394.250.287.1
5147.347.262.269.1
6121.410.394.251.2
7135.423.347.273.2
8199.456.310.316.2
9194.520.423.378.2
0240.624.456.361.3
1256.678.420.484.3
2223.763.524.438.3
3260.809.578.422.4
4278.894.663.546.4
Note: Lower explosion limit (LEL) of methane = 50,000ppm
Vc = 5.0 ± 0.2V
4
1
Fig. 2 - Basic circuit with
temperature compensation
rosneS
Table 1 - Recommended RL by sensor ID
Lot #
#07
ID #
3
2
TGS
2611
R
L
RLk( Ω htiw) ± ecnarelot%1
LEL%5 LEL%01 LEL%51 LEL%02
A
R
B
R
C
R
TGS2611
314AE #07
REF
V
RL
V
TH
R
+
-
Alarm signal
(Active = 'L')
Comparator
GND
Revised 08/03
2
APPLICATION NOTES FOR TGS2611
)
1-3 Compensation for internally generated heat
Depending on the design of the case and the
PCB, there is often a difference between the
temperature near the thermistor’s placement in
the detector and the ambient temperature.
Therefore it is recommended to measure the
actual temperature difference between the inside
and the outside of the detector and select the
value of RC according to Table 2. When RC is
selected in this manner and used in the basic
circuit (Figure 2), the result would be that
Vref=1/2 Vc.
1-4 Heater breakage detection circuit
Figure 3 shows an example of how breakage of
the sensor’s heater wire and/or heater element
can be detected. By adding R
E (3.57Ω±1%) into
the circuit and monitoring VRE, a malfunction
can be considered to have occurred when VRE
(0.2V typ.) drops to near 0V. Please note that a
circuit voltage (Vc) of 5.2V should be applied to
a circuit which incorporates a heater malfunction
detection circuit.
∆∆∆∆∆ )C˚(T
k(cR Ω)
052.8
586.7
0151.7
5156.6
0243.6
∆
T= (temp near themistor)-(temp outside detector)
Table 2 - Effect on selection of Rc by temperature
differential inside and outside of detector
Vc=5.2V
78M05
Heater breakage
signal
(Active = 'L')
GND
56mA (typ.)
R
0.05~0.1V
E
0.2V (typ.
+
-
1-5 Sensor malfunction detection circuit
Breakage of lead wires to the sensor’s electrodes
and/or sensor element can be detected by using
a circuit such as that shown in Figure 4. This
involves replacing R
C with RC1 and RC2, selecting
their values so that RC1/RC2≈35. Since VRL is
normally greater than 70mV in any atmospheric
conditions, by comparing VRL to a reference
voltage of 70mV, breakage of the lead wires and/
or sensor element can be considered to have
occurred if VRL drops below 70mV.
Figure 3 - Heater breakage detection circuit
C
V
C1
R
C2
R
Figure 4 - Sensor malfunction detection circuit
(RE = 3.57Ω±1%)
A
R
B
R
70mV (typ.)
TH
R
REF
V
+
RL
V
(RC1/RC2 ≈ 35)
-
Sensor breakage
signal
(Active = 'L')
GND
Revised 08/03
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