Tak zasilam to niesymetrycznie ponieważ mam inny wzmacniacz niż AD708 ( symbol na schemacie dołączonym) również polecany przez producenta(pełna nota katologowa). Również polecany przez producenta. Jfet pełni funkcję zabezpieczają przed napięciem wstecznym, kótre uszkodziło by czujnik. Dołączam pełną note katalogową tam piszę o tym.
APPLICATION NOTES FOR TGS5042
an ISO9001/14001 company
Application Notes for CO Detectors using TGS5042
The TGS5042 is a battery-operable
electrochemical CO sensor which is
provided with individual sensitivity
data printed on the sensor’s housing,
allowing users to eliminate the
process of calibration using CO
gas. This document offers example
circuits and important technical
advice for design and manufacture
of detectors.
Page
Sensor Marking.................................................................................2
Circuit Design
Basic Circuit.................................................................................2
Op-Amp Selection..........................................................3
Microprocessor.....................................................................3
Anti-polarization Circuit........................................................4
Amplification Circuit..............................................................5
Amplification Factor (gain)................................................................5
Leak Prevention Circuit...................................................................6
Electric Noise Prevention....................................................................6
Temperature Compensation Circuit..........................................6
Self Diagnosis Circuit.....................................................7
PCB and Housing Design
Position Dependency of the Sensor..............................................9
Thermistor Location.....................................................................9
Housing Design for Quick Response..............................................9
Sensor Lead Configuration.............................................................9
Calibration
Calibration Using CO Gas..................................................10
Calibration Using Individual Sensor Data.....................................10
Temperature Compensation.........................................11
Calculation of CO Concentration...........................................11
Manufacturing Process
Handling and Storage of Sensors..........................................12
PCB Assembly.....................................................12
Sensor Assembly..........................................................12
F i n a l A s s e m b l y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2
Gas Test.......................................................................12
Storage of Finished Products..............................................13
Packaging.................................................................13
Quality Assurance......................................................................................13
Expected Performance......................................................................................13
Frequently Asked Questions..............................................................................13
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.
TGS5042 is a UL recognized component in accordance with the
requirements of UL2034. Please note that component recognition testing
has confirmed long term stability in 15ppm of CO; other characteristics
shown in this brochure have not been confirmed by UL as part of component
recognition.
Revised 12/07
1
APPLICATION NOTES FOR TGS5042
1. Sensor Marking
Two dimensional bar code
One dimensional bar code
The TGS5042 comes with a sticker attached to
the sensor housing (see Fig. 1) which contains
individual sensor data:
FIGARO
TGS5042
Two dimensional bar code (28-digits)
XXXXZZZZZZmmmmmmnnnnnnnppppY
where:
041124
1027
Lot No.
Sensitivity to CO (nA/ppm)
XXXX = current value (nA/ppm)
ZZZZZZmmmmmmnnnnnnnpppp = serial number
(for internal tracking in production and testing)
(Ex.1027 = 1.027nA/ ppm)
Fig. 1 - Sensor markings
C1
One dimensional bar code
xxxx
where: xxx = x.xxx nA/ppm
This bar code indicates the sensor’s sensitivity
(slope) in numeric value as determined in
Figaro’s factory by measuring the sensor ’s
output in 300ppm of CO. This value is also
printed below the bar code--please note that
three decimal places should be added to the
sensitivity reading (e.g. 1027 should be read as
1.027 nA/ppm).
22�F
R1
1MΩ
IC
+
Working
TGS5042
I
Vout
Counter
Vout = I x R1
Fig. 2a - Basic circuit for
amplifying sensor current
Sensor lot number is printed below the two
dimensional bar code in YYMMDD format.
2. Circuit Design
2-1 Basic circuit
TGS5042 is a fuel cell type electrochemical sensor
with two electrodes, with sensor output current
changing linearly with CO concentration. To use
the sensor for CO detection, it is necessary to
convert sensor current to output voltage. There
are two conversion methods:
2-1a Sensor current type (see Fig. 2a)
This method directly converts sensor current into
voltage according to the following equation:
Vout = Is x R1
where: Is = Sensor output current
2-1b Load resistor type (see Fig.2b)
This method measures generated voltage across
a fixed load resistor which is connected to the
sensor electrodes. In this case, sensor output is
Revised 12/07
I
Working
I
TGS5042
R2
100k�
Vout
Counter
Vout = I x R2
Fig. 2b - Basic circuit with
fixed load resistor
expressed by the following equation:
Vout = Is x R2
where: Is = Sensor output current
The load resistor type circuit does not include an
op-amp. An op-amp is used to amplify voltage
since sensor current is very small, in which case
the circuits of the sensor current type and load
resistor type become very similar. However,
large differences in characteristics can be seen
2
APPLICATION NOTES FOR TGS5042
between amplifying current and using a fixed
load resistor.
1) Response time to CO is slower when using
a fixed load resistor (see Fig. 3). When using a
fixed load resistor, the larger the value of the
load resistor, the slower the response time. In
addition, the expected output voltage may not
be obtained if a larger than 5.6kΩ load resistor
value should be selected.
2) When amplifying current, an additional load
resistor or FET is required for anti-polarization
of the sensor.
Note 1: Please pay attention to sensor polarity.
Although the sensor’s package is physically
similar to that of a dry battery, the sensor’s
polarity is opposite to that of a dry battery.
Note 2: When voltage is applied to the sensor
output terminal, the sensor may be damaged.
Voltage applied to the sensor should be strictly
limited to less than ±10mV.
2-2 Op-amp selection
When using a fixed load resistor, in most cases
an op-amp is required to amplify the sensor’s
small output voltage.
Rail-to-Rail Op-Amps such as the following
are recommended for both basic conversion
circuits:
AD708, AD8698, OP07 (Analog Devices),
TLC272(TI), OPA177(BB), MCP6042 (Microchip),
OPA2355 (TI)
Please note for circuits employing an op-amp,
when a fixed load resistor is used for antipolarization, only an op-amp with small leak
current (such as AD708 , OPA2355) can be used.
When an op-amp with large leak current is used,
offset voltage may fall outside of the adjustable
range by leak current. (see 2-4 Anti-polarization
Circuit).
To obtain high accuracy in an analog circuit, an
op-amp with a zero adjustment function, such
as LF356 (National), is recommended. In Figure
4, a typical zero-span adjustable circuit using
LF356 is shown.
Revised 12/07
3.5
Op-Amp type
Resitor type (5.6k_)
Resitor type (1.0k_)
CO400ppm
3
2.5
CO 150ppm
2
CO 70ppm
Vout (V)
1.5
CO 30ppm
1
0.5
0
0
200
400
600
800
1000
1200
1400
Time (sec.)
Figure 3 - Sensor response curve in various
basic circuits (amplified 3.13M times)
C1
VR2
R2
100k�
Working
+
IC
TGS5042
Counter
Vout
VR1
VR1: Variable resistor for zero adjustment
VR2: Variable resistor for span adjustment
Figure 4 - Circuit example for zero adjustment
2-3 Microprocessor
Incorporating a microprocessor into a circuit
offers several advantages. The complex
calculation of alarm concentration based on
COHb and temperature compensation can be
carried out by the microprocessor, simplifying
circuit design. By recording sensor sensitivity
data from the sensor’s bar code label in the
microprocessor and by using the microprocessor
to compensate for offset voltage, the calibration
process for detector production can be greatly
simplified. In addition, useful values such as
a maximum CO concentration and a sensor
output timing chart can be recorded in the
microprocessor as additional functions.
3
APPLICATION NOTES FOR TGS5042
From the viewpoint of signal resolution, the
recommended specification of a microprocessor
is 10 bit or higher.
2-4 Anti-polarization Circuit
When the sensor is stored without connection
between the working electrode (W) and counter
electrode (C), polarization will occur between the
electrodes. When a polarized sensor is connected
to an operating circuit, it takes a long time to
stabilize sensor output (refer to 3-5 Influence of
Storage in TGS5042 Technical Information).
C1
22�F
R2
1.2M�
A sensor current type circuit can use three
methods for anti-polarization:
3) JFET (Figs. 7 and 8)
This method is normally used in CO alarms
without an external switch. In this case a JFET
(Field Effect Transistor) is recommended.
Junction type transistors are not recommended
due to their large leak current. MOSFETs cannot
be used.
Revised 12/07
IC
AD708
R1
1k�
Vout
Counter
Figure 5 - Anti-polarization circuit using
a fixed resistor
C1
22�F
R2
Vcc
Working
100k�
-
SW
+
IC
AD708
TGS5042
Vout
Counter
1) Fixed resistor (Fig. 5)
As a simple method, a fixed load resistor can be
used. In this case, it is necessary to use an opamp with very low leak current (such as AD708
or OPA2355). Op-amps with large leak current
may cause offset voltage to fall outside of the
adjustable range.
2) External switch (Fig. 6)
This method is normally used for CO analyzers
where there is an external switch to control
power on/off. By using an external switch, the
connection between the W and C electrodes can
be controlled, whether open or short ( & lt; 1kΩ)
circuit.
+
TGS5042
To avoid polarization during storage, it is
necessary to keep a short-circuit (or & lt; 1kΩ
resistance) between the electrodes. In this
manner, measures such as a timed warm-up
period for stabilizing the sensor are not required
in circuit design.
In a load resistor type circuit, it is not necessary
to add additional parts for anti-polarization
since the circuit already contains a load resistor
between the sensor electrodes.
-
Working
Figure 6 - Anti-polarization circuit using
an external switch
C1
22�F
R2
1.2M�
Working
-
JFET
(N-Channel)
+
IC
TGS5042
Vout
Counter
1.5V or more of baseline is required
for baseline to operate JFET
Figure 7 - Anti-polarization circuit using
an N-channel JFET
4
APPLICATION NOTES FOR TGS5042
It is necessary to choose a P-channel or Nchannel FET, depending on the required effective
output range, gain, and the variation range of
Vcc. Figures 7 and 8 show the basic circuit for
each type.
The advantage of a P-channel FET is a wider
effective voltage range. However P-channel
FETs have higher cost, weakness against
applied voltage fluctuation, and they require
higher operating voltage than 5V (making them
unsuitable for applications which need & lt; 5V).
Recommended P-channel FETs are J177, J270
(Fair Child), and 2SJ103 (Toshiba).
N-channel JFETs are widely available in many
models, have lower cost, and are more stable
to voltage fluctuation of power supply. Their
disadvantage is their narrower effective voltage
range. However, one option to extend their
effective voltage range is to shift baseline to Vcc
as shown in Fig.9. In the example circuit, output
voltage decreases with a CO concentration
increase. Recommended N-channel JFETs
are J201, PN4117 (Fair Child), and 2SK117
(Toshiba).
C1
22�F
Vcc
1.2M�
-
Working
+
TGS5042
2-6 Amplification Factor (gain)
It is necessary to decide gain by selecting Vcc,
JFET and the op-amp in terms of sensor output
range, target gas concentration range, and
required accuracy.
Revised 12/07
IC
Vout
JFET
(P-Channel)
Counter
Figure 8 - Anti-polarization circuit using
an P-channel JFET
C1
22�F
R2
3.0V
1.2M�
-
Counter
JFET
(N-Channel)
+
3.0V of baseline is set
to operate JFET.
IC
TGS5042
Vout
Working
Vout decreases by a CO
concentration increases.
2-5 Amplification Circuit (see Figs. 10 and 11)
In a load resistor type circuit, voltage can be
amplified by using either an inverted or noninverted amplifier. Depending on the method,
the gain is slightly different. Please note that
direction of W and C electrodes are opposite
between non-inverting and inverting amplifier
circuit.
Non-inverting amplification has lower leak
current from the sensor to the op-amp since the
working electrode is connected to the positive (+)
terminal of the op-amp. To prevent leak current,
setting a voltage follower between sensor output
and the op-amp is recommended (refer to Sec. 2-7
Leak Current Prevention Circuit).
R2
Figure 9 - Circuit for extending effective
voltage range using N-channel JFET
C1
22�F
R2
100k�
V1= - (I xR1)
-
Working
TGS5042
R3
1k�
I
+
IC
AD708
R1
1k�
Vout
Counter
Vout = I x R1 x (R2/R3)
Figure 10 - Inverting amplifier circuit
5
APPLICATION NOTES FOR TGS5042
C1
22�F
R2
100k�
V1= I x R1
+
Counter
TGS5042
I
2-9 Temperature Compensation Circuit
Temperature compensation can be done in one
of two ways:
1) Input the thermistor ’s signal into the
Revised 12/07
Vout
Vout = I x R1 x (1+R2/R3)
Figure 11 - Non-inverting amplifier circuit
C1
22�F
R2
V1= - (I xR1)
100k�
IC 1
+
Working
R3
Current to Op-Amp
will be shut out.
R1
1k�
I
TGS5042
IC 2
+
1k�
Vout
Counter
Vout = I x R1 x (R2/R3)
Figure 12 - Leak current measure
using a voltage follower
Three options to prevent electrical noise:
1) Use an electrical noise filter
2) Use a voltage follower (see Sec. 2-6 Leak Current
Prevention)
3) Build up an RC network with a resistor and
capacitor in place of the feedback resistor of the
op-amp. The recommended time constant (T) of
RC circuit for power input is ≤2.5 seconds sinc
ethe value in the basic recmmended circuit is
2.2 seconds.
Temperature compensation
circuit
C5
+
C2
+
T22uF/16V
R7
T2.2uF/16V
R2
IC1A
AD708JN
1
R4
5
10k
R3
6
10k
+
IC1B
7
-
R8
3
10k
1
8
+
2
AD708JN
+
IC2
4
3
1k
06P 10k
VR2
1
A
R6
1.5V
C3
R9
10k at 20˚C
B: 3380
10.0k
A
VR3
50k
2SK117
0.1u
2
4
+
12k
DINS4
110k
RT
310k
VCC
9.1k
CN1
MB5P-90S
D1
C1
REG1
1
2
3
4
5
680JT
VCC
Tr 3
5
BATT1
UM3XI
7
1
2
T33u/16V
To prevent external electrical noise, setting a
noise filter inside the detector and making a noise
prevention circuit pattern is recommended.
R3
1k�
Working
2-7 Leak Current Prevention Circuit (Fig. 12)
In a fixed load resistor circuit, a non-inverting
amplifier circuit is recommended for simplicity.
For further countermeasures, adding a voltage
follower circuit between sensor output and the
op-amp is recommended.
2-8 Electrical Noise Prevention
Since sensor impedance is 10Ω or less, the
sensor itself will not be a source of electric
noise. However, the sensor is easily influenced
by external electric noise since sensor output is
very small in both basic circuits. Therefore, it
is necessary to incorporate measures into the
circuit pattern and power supply to eliminate
electrical noise.
IC
R1
1k�
VR1
R5 67W 5k R1
For example, a gain of at least 2.5 million is
calculated to be necessary for the following
example CO detector:
- 5V Vcc
- 10 bit microprocessor
- Accuracy: ±20% of reading
- Detection range: 0 ~ 750ppm
To extend the detection range, it is necessary
to increase Vcc or to use a microprocessor with
higher resolution.
NJU7031D
6
C4
0.1u
VCC
RT: NTSA0XH103FE1B0 (Murata: Axial type)
VR1, VR2: Zero adjust
VR3: Span Adjust
Fig.13 - Temperature compensation in discrete circuit
Figure 13 - Temperature compensation circuit
6
APPLICATION NOTES FOR TGS5042
Self test current control
Self test drive control
Tr 1
Microprocessor port2
H-Z on
0V off
2SK982
R10
Microprocessor port1
2M
C2
Vcc on
0V off
R11
1M
0.1�
A
1
2
R2
BATT1
UM3XI
Tr 3
2SK117
3
VCC1
C3
MCP6042
0.1�
+
IC1
8
8
A
1
5
4
1.0k
0.1�
2
2.0V
3.0k
A
VCC1
C3
680JT
33�/50V
REG1
C1
+
VR1
R5 67W 10k R6
CN1
MB5P-90S
+
T1�/16V
C4
1
2
3
4
5
D1
DINS4
1.2M
6
MCP6042
+
7
IC1
-
4
VCC
5V
Tr 2
2SK117
Figure 14 - Self diagnosis circuit
microprocessor and compensate it with the
temperature compensation table which is also
stored inside microprocessor (refer to Sec 3Calibration for details of the compensation process,
and refer to Appendix 1 for temperature compensation
factors).
2) Make an analog circuit with a negative
temperature coefficient(NTC) thermistor and
resistors in place of the feedback resistor of IC2
(see Fig.13)
2-10 Self Diagnosis Circuit (patented by Figaro)
Sensitivity to CO would be lost in case
several failure modes were to occur, such as
wire breakage, short circuit, or in case the
sensor’s water reservoir were to dry up. By
using Figaro’s patented self diagnosis circuit,
malfunctions involving loss of CO sensitivity
can be detected.
Please note that this method cannot detect CO
sensitivity loss caused by lack of gas diffusion
when dust or water droplets cover the pin
Revised 12/07
holes for gas diffusion. In addition, slight loss
of CO sensitivity cannot be detected by selfdiagnosis.
Depending on the user’s circuit design, factors
for self diagnosis such as current value, self
diagnosis period, measurement timing, and
voltage range for judgement may vary. Therefore,
it is recommended that experimentation with the
user’s circuit be conducted for fine tuning these
factors in self diagnosis.
Figs. 14, 15, and 16 show examples of the circuit,
timing chart, and process chart.
The basic steps of self-diagnosis are:
1) Temporarily cut the sensor off from the circuit
Activate a transistor (TR2) to temporarily isolate
the sensor from the circuit so that self test may
be conducted without activating an alarm.
2) Apply a minute current to the sensor
Activate a transistor (TR1) and apply about
1µA (absolute maximum rating: 5µA), which
simulates exposure to about 1000ppm CO. This
7
APPLICATION NOTES FOR TGS5042
current should be applied for 2~5 seconds. If the
sensor is normal, sensor current will be output
and then quickly recover to its base level.
3) Reconnect the sensor to the circuit
1~2 seconds after self diagnosis current is
terminated (TR3 is reset), activate TR2 and
reconnect the sensor to the circuit. Then current
applied to the sensor will be discharged.
4) Self diagnosis determination is carried out
Approx. 5 seconds after the sensor is reconnected
to the circuit, if the sensor output falls within the
range of 2.3 ~ 3.8V (normal output expected in
1000ppm of CO), which corresponds to 0.4 to
2µA of sensor current, the sensor can be judged
to have normal CO sensitivity. If the sensor
output is ≥3.8V, the sensor is judged to be short
circuited. If the sensor output is & lt; 2.3V, the sensor
is judged to be open circuited. Please refer to Fig.
17 for the Vout pattern corresponding to each of
these cases.
H-Z (on)
0V (off)
approx. 1 min.
VCC (on)
Self test
current
control
0V (off)
approx. 5 sec.
Revised 12/07
0.01 - 1sec.
0.01 - 1sec.
Measuring point
5 - 7 sec. after changing to 0V for drive port
Figure 15 - Self diagnosis timing chart
Power on (Normal)
Drive control: H-Z (on)
Current control: 0V (off)
Normal mode
Sensor output recovers to its initial level about
1 minute after the sensor judgement in the
step 4 above. The total self diagnosis time for
Steps 1-4 is 1~2 minutes. Please note that the
larger or longer current is applied to the sensor,
the longer it takes to complete self diagnosis.
The self diagnosis process should be carried
out periodically to ensure that the sensor has
sufficient CO sensitivity to afford protection.
The recommended self diagnosis interval for
the circuit in Fig.14 is 180 seconds or more.
To shorten the interval, it is recommended to
Normal
Drive
control
Note: The above Vout range is valid only
for the circuit shown in Fig.14. When gain
of amplification and/or measuring timing is
different, the Vout range would be changed.
Note:
Please restart normal operation mode when
sensor output recovers to its initial level after
the self diagnosis operation. The interval
between self diagnosis operations should be set
considering the recovery period for the sensor.
If current is applied to the sensor before it can
recover to its initial level, the sensor may be
damaged due to overcharging.
Self test
for sensor
Normal
Drive control: H-Z (on)
Current control: 0V (off)
Self test ?
NO
Yes
Drive control: H-Z (on) to 0V (off)
0.1 - 1 sec.
Current control: 0V (off) to VCC (on)
5 sec.
Current control: VCC (on) to 0V (off)
0.1 - 1 sec.
Drive control: 0V (off) to H-Z (on)
5 - 7 sec.
Measure the output voltage (Vout)
Yes
Vout = 2.3 - 3.8V?
NO
Trouble signal
Figure 16 - Self diagnosis flow chart
8
APPLICATION NOTES FOR TGS5042
Drive : H-Z
0V
Current: VCC
0V
5 - 7 sec.
5 sec.
5
Vout/V
4
Normal range
2.3 - 3.8 V
3
2
1
0
0
10
20
30
40
Time/sec.
50
60
Normal sensor
Drive : H-Z
0V
Current: VCC
0V
Drive : H-Z
0V
Current: VCC
0V
5
5
4
Vout/V
Vout/V
4
Normal range
2.3 ~ 3.8V
3
2
2
1
1
0
Normal range
2.3 ~ 3.8V
3
0
10
20
30
40
50
0
60
0
10
20
50
60
50
60
Drive : H-Z
0V
Current: VCC
0V
5
5
4
Vout/V
4
Vout/V
40
No sensitivity
Open circuit
Drive : H-Z
0V
Current: VCC
0V
Normal range
2.3 ~ 3.8V
3
2
Normal range
2.3 ~ 3.8V
3
2
1
1
0
30
Time/sec.
Time/sec.
0
0
10
20
30
40
50
60
0
10
20
30
40
Time/sec.
Time/sec.
Water/electrolyte dried up
Short circuit
Figure 17 - Self diagnosis Vout response patterns
minimize the current applied to the sensor (less
current/shorter duration). However, the smaller
the current, the more difficult to distinguish
between normal sensors and abnormal sensors.
Users should conduct a verification test using
their actual circuit.
3. PCB and Housing Design
3-1 Position Dependency of the Sensor
TGS5042 has no position dependency in normal
usage such as in residential CO detectors.
However, for applications where ambient
temperature can change drastically and suddenly
to less than -20°C, it is recommended that the
sensor should be placed in a vertical position
with the working electrode upward. If the
sensor is positioned horizontally or vertically
with the working electrode down, the sensor
may be structurally damaged by large volume
Revised 12/07
expansion if water in the reservoir freezes.
3-2 Thermistor Location
It is recommended that a thermistor is located
as near to the sensor as possible in order to
accurately measure ambient temperature around
the sensor.
3-3 Housing Design for Quick Response
For applications where quick response is
required, such as for simple CO analyzers, it is
recommended that the gas inlet of the sensor be
located at the detector slits or opening. It is also
recommended to make a small compartment
with slits in at least two sides (see Fig.18).
3-4 Sensor Lead Configuration
There are two lead configurations for TGS5042.
The best version will depend on the user ’s
9
APPLICATION NOTES FOR TGS5042
application.
1) Sensor compartment
TGS5042-A00: Sensor with SUS lead pins
The hard pins enables the sensor to be mounted
directly to the PCB, simplifying the assembly
process.
TGS5042-B00: Sensor with flexible nickel ribbon
The flexible nickel ribbon allows for a variety of
methods for connection to the PCB. This type
is also suitable for insertion into a socket. The
flexible nickel ribbon may be broken by strong
mechanical shock, drop, or vibration, so it is
recommended that the sensor body be affixed
onto the PCB by using two-sided tape or wire,
for example.
4. Sensor Calibration
4-1 Calibration Using CO Gas
1) After powering the circuit, wait 5 minutes to
stabilize sensor output in clean air (see Note 1)
2) Measure sensor output in clean air (V0) (See
Note 2)
3) Inject C1ppm of CO gas
4) After stabilizing sensor output (eg. 3 to 4 min),
measure sensor output (V1)
5) Calculate sensor sensitivity α from V0 and
V1 values:
α = (V1-V0) / C1
Using this method, accuracy of ±5% can be
obtained for display readings. Please note that
temperature should be in the range of 20°C±2°C
during the calibration process since the sensor
has dependency on temperature.
Note 1: In principle, due to the nature of
electrochemical cells, pre-heating before
calibration is not required. However, in actual
manufacturing, it is recommended to wait 5~10
min. before calibration to stabilize sensor output
in the circuit.
Note 2: If CO gas is present during the zero
adjustment process, a correct zero adjustment
cannot be carried out. A detector should be
checked in advance to verify that it generates
output corresponding to CO a concentration less
than 10ppm after subtracting detector output
Revised 12/07
2) Slits
Figure 18 - Sensor compartment design
without sensor.
4-2 Calibration Using Individual Sensor Data
Using individual data printed on sensor, which is
measured at Figaro factory before shipping, can
considerably simplify the calibration process.
Though the expected accuracy of ±15% accuracy
in this method is less than that for using CO gas,
this method can achieve significant reduction
in handling costs while achieving acceptable
accuracy.
4-2-1 Input sensitivity data into microprocessor
Sensor data from the label can be read into the
microprocessor in one of three ways:
1) Manually input the user readable value on the
label, located beneath the one dimensional bar
code (this value is nA/ppm and contains three
decimal places).
2) Using a barcode reader which can read Code128, read the one dimensional barcode and input
directly to the microprocessor (this value is nA/
ppm and contains three decimal places).
3) Using a barcode reader with software which
can read Data Matrix format, read the 2dimensional bar code. Data should be written
into an EEPROM via personal computer and by
converting the text format into a proper format
for the EEPROM.
10
APPLICATION NOTES FOR TGS5042
4-2-2 Compensation of offset voltage (zero
adjustment)
To compensate for offset voltage which is created
by the sensor and operational amplifier, measure
the offset voltage (V0) in clean air (0ppm of CO)
and write into an EEPROM or a microprocessor.
This value should be read from the finished
detector (after installation of sensor, op-amp,
etc.).
To obtain higher accuracy, keep ambient
temperature in a range of 20±10°C and be sure
that the ambient air is completely free of CO.
4-3 Temperature Compensation
There are two methods for temperature
compensation:
1) Using a microprocessor
In case of using a microprocessor, it is necessary
to read the thermistor output and write it into
the microprocessor. Inside the microprocessor,
temperature compensation is carried out by
using the compensation coefficiency table shown
in Appendix 1. Temperature compensated CO
sensitivity (αt) is calculated by the following
equation:
αt= α/CF
where: CF = compensation coefficient at certain
temperature
2) Without using a microprocessor
In case of not using a microprocessor, this
process can be eliminated.
4-4 Calculation of CO Concentration
CO concentration can be calculated by using
sensor output (Vout), offset voltage (V0),
temperature compensated CO sensitivity (t), and
gain (A) in the following formula:
C = (Vout-Vo)/A/αt
Equation 1
Depending on the op-amp, offset voltage has
a large temperature dependency as shown
in Fig.19. To compensate the temperature
dependency, it is recommended to make a table
of offset voltage at different temperatures Vo(T)
in the microprocessor, and Vo in Equation 1
should be replaced to Vo(T) in Equation (1’).
Revised 12/07
30
NJU7034
AD708
20
10
0
Display reading (ppm)
-10
-20
-30
-20
-10
0
10
20
30
40
50
60
70
Temperature (˚C)
Figure 19 - Temperature dependency of offset voltage
for op-amps
Power ON
Alarm dalay againt
polarity of sensor
Generate trouble
signal
Yes
Sensor trouble
detection
No
Sensor output
sampling
Thermistor
output sampling
CO calculation
Display CO
concentration
Convert to COHb
concentration
Activate CO alarm
Yes
Alarm
determination
No
Suppress CO alarm
Figure 20 - Signal processing
flow chart
C = (Vout-Vo)/A/αt
Equation 1’
Actual gain (A) should be measured instead
of calculated or specified at a theoretical value
since such value may not be obtained in actual
measurement.
Fig.20 shows basic flow chart of signal
processing.
11
APPLICATION NOTES FOR TGS5042
No.
Soldering material
Company
3
Solder
Coat Co.,
L td .
4
Model
Composition
Melting Temp
Company
Model
H63E
1
2
Flux
Sn/37Pb
183˚C
Tamura Kaken Corp
ULF-250
(Cl free)
H63E
Sn/37Pb
183˚C
Asahi Chemical Research
Laboratory Co., Ltd.
AGF-780R
H63A
Sn/37Pb
183˚C
Asahi Chemical Research
Laboratory Co., Ltd.
AGF-550BK
LLS219A-B18
(pb free)
Sn/3.0Ag/0.5CuNi/Ge
Soldus line: 271˚C
Liquidus line: 221˚C
Tamura Kaken Corp
EC-19S-8
Table 1 - Wave soldering materials
5. Manufacturing Process
5-1 Handling and storage of sensors
Prior to usage, sensors should be stored in
Figaro’s original sealed bag under conditions
of 5~30˚C, 30~80%RH, and avoiding dew
condensation for a maximum period of 6
months. Do NOT use a moisture proof bag (such
as an aluminum coated bag) for prevention of
dew condensation. When the sensor is shipped
from Figaro, the sensor electrodes are short
circuited. Please maintain this condition during
storage. If stored in open circuit condition,
sensor polarization will occur, requiring a long
warm up period for stabilization of output.
5-2 PCB assembly
Flux should be sufficiently dried before sensors
are assembled onto the PCB to avoid any
contamination of the sensor by flux vapors.
5-3 Sensor assembly
The sensor electrodes are short circuited with an
SUS spring attachment for –A00 model, while
the -B00 model is shorted by the Nickel ribbon
when the sensors are shipped. Before mounting
the sensors on a PCB, remove the spring from
the –A00 model. On the –B00 model, the Nickel
ribbon should be cut. Both versions can be
directly soldered onto a PCB.
In case the –B00 model is inserted into a socket,
it is recommended to cut Ni ribbon as short as
possible from the welded part. Do NOT peel
away the Nickel ribbon with strong force at the
working electrode side. The mechanical force
Revised 12/07
may damage the sensor electrode.
The metal ribbon of the -B00 model are for
electrical connection and therefore should not be
used to affix the sensor to a PCB. For securingthe
sensor to a PCB and to prevent disconnection of
the Ni leads, the sensor should be attached to a
PCB using wire, two-sided tape, etc.
Recommended conditions for manual
soldering:
Temperature of soldering copper head: 380°C
Period: & lt; 10 sec.
Figaro has confirmed that wave soldering can
be done by using the materials shown in Table
1. When different materials will be used, a test
should be conducted before production starts
to see if there would be any influence to sensor
characteristics.
5-4 Final assembly
Avoid any shock or vibration which may be
caused by air driven tools. This may cause
breakage of the sensor’s lead wires or other
physical damage to the sensor.
5-5 Gas test
Test all finished products in the target gas
under normal operating conditions. Keep the
atmospheric conditions in the chamber stable,
utilizing a user-defined standard test condition
which is based on applicable performance
standards and on anticipated usage for detectors.
Remove any traces of smoke, adhesives, gases,
or solvents from the chamber.
Do NOT use Nitrogen balanced CO gas. Oxygen
12
APPLICATION NOTES FOR TGS5042
molecules are required for the reaction of the
sensor with CO (refer to Sec. 2-Operation Principle
of TGS5042 Technical Info).
During exposure to a mixture of CO and N2,
the sensor reacts to CO by consuming oxygen
molecules inside sensor. After consuming all the
oxygen molecules inside sensor, the sensor will
not react to CO.
Acceptance of sensor
Read out
sensitivity data
Input sensitivity data to
EEPROM
Sensor Assembly
Zero adjust
Final Assembly
(PCB,Casing,etc.)
5-6 Storage of Finished Products
Detectors should be stored in a clean air
environment at room temperature. Avoid
storage in dirty or contaminated environments.
Avoid storage in extremely low humidity-sensor life may be shortened. Please refer to Sec.
6-Notes in TGS5042 Technical Info for additional
information.
6. Quality Control
1) A sample of finished products from each
production lot should be tested to confirm alarm
concentration. Check whether these samples are
acceptable for shipment and maintain a record
of these tests.
2) Periodically sample a certain number
of finished products to confirm the alarm
concentration under extreme conditions (e.g.
-10°C or 40°C/85%RH) and maintain a record
of these tests.
3) Periodically sample a certain number of
completed products periodically to confirm their
long-term characteristics and maintain a record
Revised 12/07
NG
OK
NOTE: Without testing after final assembly,
detectors have no guarantee of accuracy or
reliability.
Never expose the sensor to a vacuum. Sudden
exposure to a vacuum may temporarily damage
the sensor.
Repair
PCB Assembly
Circuit test
Dry/bottled CO gas can be used since the
sensor’s humidity dependency is very small.
5-7 Packaging
When a plastic clam shell is used for packaging
of a CO detector, a small charcoal filter should
be placed inside to avoid potential influence by
organic vapors generated from the package.
Acceptance of components
Re-calibration
(Zero, Gas)
Gas test
NG
Function check
OK
Packaging
Storage
Shipping
Figure 21 - Manufacturing flow chart
of such tests.
7. Expected Performance
Considering sensor variation as well as the
tolerances of electric components such as the opamp and thermistor, display accuracy of ±20%
can be expected when individual bar code data
of TGS5042 is used for calibration. This level
of accuracy may not be obtained if low quality
components are used. For higher accuracy, gas
calibration for each sensor is recommended.
8. Frequently Asked Questions
Q: What approvals does TGS5042 have?
A: The sensor has received UL2034 component
recognition.
Q. How long is the expected life of TGS5042?
A: Unlike some electrochemical sensors which are
short-lived, the expected sensor life is more than 5
13
APPLICATION NOTES FOR TGS5042
years under normal operating condition. The expected
output change is only 2% after 2000 days in normal
air.
Q: Is it true that the accuracy of two-electrode
electrochemical CO sensors is less than that of threeelectrode type sensors?
A: While this may be true for sensors whose electrode
potentials are unstable, the TGS5042 exhibits good
accuracy. With an optimized sensor structure and
electrodes, TGS5042 maintains very stable electrode
potentials. As a result, the sensor shows excellent long
term stability, drifting by only 2% over 2000 days.
Q: Where does CO gas enter into the sensor?
A: There are three pin holes in the working electrode
which act as a gas inlet. Refer to Figure 1 on page 2
of the TGS5042 Technical Information.
Q: Does the sensor comply to RoHS restrictions?
A: Yes.
Q: For what purpose are the sensor electrodes short
circuited during storage?
A: The electrodes are short circuited to prevent
polarization. When the sensor is stored without
connection, it takes a long time to stabilize sensor
output for sensor operation. This phenomenon is
not related to sensor life. Refer to Sec. 3-4 Antipolarization Circuit.
Figaro USA Inc. and the manufacturer, Figaro
Engineering Inc. (together referred to as Figaro)
reserve the right to make changes without notice to
any products herein to improve reliability, functioning
or design. Information contained in this document is
believed to be reliable. However, Figaro does not
assume any liability arising out of the application or
use of any product or circuit described herein; neither
Q: Are any special precautions needed to use
TGS5042 for a simple CO analyzer?
A: To obtain quick response, the gas inlet of sensor
of the sensor should be located nearest to the detector
slits or opening. For this application, TGS5042-B00
is recommended. Please cut the Nickel ribbon as
short as possible and connect an insulated copper
wire by soldering. In addition, it is recommended to
make small compartment with slits at least in two
sides around the sensor. Refer to Sec. 3-3 Housing
Design for Quick Response.
Q: How can electric noise be prevented?
A: Since sensor impedance is 10Ω or less, the sensor
itself will not be a source of electric noise. However,
the sensor is easily influenced by external electric
noise since sensor output current is very small.
Power-supply noise should be minimized, an antielectrical noise circuit pattern should be made, and
a CR circuit should be used to prevent influence of
electrical noise.
If incoming noise is too large to be prevented by
the above measures, these additional steps should
be taken:
- coat the detector case with a copper board
- use anti-EMI material
- place metal mesh around the electric circuit
does it convey any license under its patent rights, nor
the rights of others.
Figaro’s products are not authorized for use as critical
components in life support applications wherein a
failure or malfunction of the products may result in
injury or threat to life.
FIGARO GROUP
HEAD OFFICE
Figaro Engineering Inc.
1-5-11 Senba-nishi
Mino, Osaka 562-8505 JAPAN
Tel.: (81) 72-728-2561
Fax: (81) 72-728-0467
email: figaro@figaro.co.jp
www.figaro.co.jp
Revised 12/07
OVERSEAS
Figaro USA Inc.
121 S. Wilke Rd. Suite 300
Arlington Heights, IL 60005 USA
Tel.: (1) 847-832-1701
Fax.: (1) 847-832-1705
email: figarousa@figarosensor.com
14
APPLICATION NOTES FOR TGS5042
Appendix 1 - Temperature Compensation Coefficients
Temp.
(˚C)
Temp.
(˚C)
CF
(I/Io)
Temp.
(˚ C )
CF
(I/Io)
-40
0.453
0
0.844
40
1.105
-39
0.463
1
0.852
41
1.109
-38
0.473
2
0.861
42
1.112
-37
0.483
3
0.870
43
1.115
-36
0.493
4
0.878
44
1.118
-35
0.503
5
0.887
45
1.121
-34
0.513
6
0.895
46
1.124
-33
0.523
7
0.903
47
1.126
-32
0.534
8
0.911
48
1.128
-31
0.544
9
0.919
49
1.130
-30
0.554
10
0.927
50
1.132
-29
0.564
11
0.935
51
1.134
-28
0.574
12
0.943
52
1.135
-27
0.584
13
0.950
53
1.136
-26
0.594
14
0.958
54
1.137
-25
0.605
15
0.965
55
1.138
-24
0.615
16
0.972
56
1.139
-23
0.625
17
0.980
57
1.139
-22
0.635
18
0.987
58
1.139
-21
0.645
19
0.994
59
1.139
-20
0.655
20
1.000
60
1.139
-19
0.664
21
1.007
61
1.139
-18
0.674
22
1.013
62
1.139
-17
0.684
23
1.020
63
1.139
-16
0.694
24
1.026
64
1.139
-15
0.704
25
1.032
65
1.139
-14
0.714
26
1.038
66
1.139
-13
0.723
27
1.044
67
1.139
-12
0.733
28
1.050
68
1.139
-11
0.742
29
1.055
69
1.139
-10
0.752
30
1.060
70
1.139
-9
0.761
31
1.066
-8
0.771
32
1.071
-7
0.780
33
1.076
-6
0.789
34
1.080
-5
0.799
35
1.085
-4
0.808
36
1.089
-3
0.817
37
1.094
-2
0.826
38
1.098
-1
Revised 12/07
CF
(I/Io)
0.835
39
1.101
15