Abstract: TGS4160 is FIGARO (Fujia logic) produced a solid-state electrochemical model of carbon dioxide (CO2) sensor, the device in addition to a small size, long life, good selectivity and stability characteristics, but also resistant to high wet and low temperature characteristics. Which can be used in automatic ventilation system or the long-term monitoring of CO2 gas applications. This paper describes the internal structure of the sensor and the working principle of a special module with TGS4160 design the basic application circuit diagram.
  Key words: TGS4160; SCM; sensor; carbon dioxide
  1 Overview
  TGS4160 carbon dioxide sensor is FIGARO (Fu Jialuo) produced by solid-state electrochemical-type gas sensors. The carbon dioxide sensor in addition to a small size, long life, good selectivity and stability characteristics, but also the characteristics of low temperature and humidity resistant can be widely used for automatic ventilation system or the long-term monitoring of CO2 gas applications occasions. However, due to TGS4160 longer warm-up time (usually 2 hours), so the device more suitable for power at room temperature for a long time continuously. In addition, for the convenience of customers, FI-GARO company also designed with a temperature compensation sensor processing module AM-4. The module microprocessor control, CO2 gas concentration in the output signal level is 0.0 ~ 3.0V, the equivalent concentration of 0 ~ 3000ppm, and a relay transfer control port can output high and low threshold signals used for external control. TGS4160 sensor main technical parameters are as follows:
Measuring range: 0 ~ 5000ppm;
life: 2000 days;
heater voltage: 5.0 ± 0.2VDC;
Heater current: 250mA;
  Heater power consumption: 1.25W;
  internal thermal resistance (Compensating): 100kO ± 5%;
  Operating temperature: -10 ~ +50

  Use the humidity ? 5 ~ 95% RH;
  Product Size: The maximum diameter F24mm, high 24mm, pin length of 5.8mm.
  2 internal structure
  TGS4160 carbon dioxide sensor is a hybrid containing CO2 thermistor sensor. The device between the two electrodes is filled with cation solid electrolytes. Its gold-plated cathode material of lithium carbonate and made the anode is gold-plated material. Lining the base of the sensor is polyethylene terephthalic ester and glass fiber reinforced, and then do cylindrical mesh of stainless steel package. Components of the inner layer of 100 mesh stainless steel mesh set in nickel plated brass ring, and is used with high strength resin adhesive and base lining fixed together. The outer layer of the top cover 60 has the purpose of cast stainless steel mesh. In order to reduce the effects of interfering gases purpose, TGS4160 between the inner and outer layers of stainless steel mesh is also filled with adsorbent material (zeolite). Sensor 0.1mm 6-pin through the foil conductor and internally connected. The equivalent of the internal structure shown in Figure 1. Figure, the anode and the sensor pin 3 S (+) connected to the cathode pin and the sensor 4 of S (-) connected, Pt heaters and sensors connected to the first 1,6 feet, the internal thermal resistance and the sensor s 2,5 feet connected. The role of the internal thermal resistance of the resistor by detecting the ambient temperature for temperature compensation of the sensor, so that the corrected measurement is more accurate.

  3 Works
  TGS4160-type CO2 sensor is an electrochemical-type gas sensor, when exposed to the elements in the CO2 gas environment, it will have electrochemical reaction. The reaction is as follows:
  Cathodic reaction equation:
  4Li + +2 CO2 + O2 +4 e-= 2Li2CO3
  Anodic reaction equation:
  4Na + + O2 +4 e-= 2Na2O
  The overall chemical reaction equation:
  Li2CO3 +2 Na + = Na2O +2 Li + + CO2
  As a result of electrochemical reaction, according to Neste equation (Nernst), the process will produce the following potential (EMF):
  EMF = Ec-(RF) / (2F) ln (PCO2)
  Where: PCO2 is the partial pressure of CO2; Ec is a constant; R is the gas constant; T is temperature (K); F is the Faraday constant.
  Seen from the above formula, by monitoring the S (+), S (-) generated between two electrodes the potential value of the EMF, the concentration of CO2 to the value can be measured. In order to keep the most sensitive of the sensor temperature, the general need to provide heating voltage for heating the heater, but the heating voltage change will directly affect the stability of the sensor, so the heating voltage must be stable, its scope should be 5.0 ± 0.2VDC within. To ensure the CO2 in the accurate measurement, in addition to ensuring the heating voltage stability and environmental temperature changes in temperature compensation, the main thing is to measure between the two electrodes changes the electrical potential value EMF, rather than the absolute potential value of the EMF, as EMF and CO2 between the concentration of a good linear relationship. Although the absolute EMF increases with temperature rise, ?EMF has remained constant, and it is -10  ~ +50 temperature range, independent of temperature.
  Figure 2
  EMF value obtained by the following formula:
  EMF = EMF1-EMF2
  Which, EMF1 to 350ppm of CO2 in the EMF value; EMF2 to the measured values of CO2 in the EMF.
  At a temperature of 20  ± 2 , humidity 65 ± 5% RH, the heating voltage of 5.0 ± 0.05VDC, warm-up time is 7 days or more than 7 days under the conditions of the sensor measured at a concentration of 350ppm in the EMF value is 220 ~ 490mV, while ?EMF at 350 ~ 3500ppm of CO2 concentration in the value is 44 ~ 72mV, so the actual measurement applications circuit, according to the characteristics of the sensor requirements, in addition to the use of high input impedance (= 100GO), low bias current (= 1pA) of the operational amplifier, but also on the measured signal for processing. There are usually two of the signal processing options are available: one using Figaro (FIGARO) FIC98646 company dedicated processor module, and second, use of other types of microcontrollers and programming, through their own signal processing.
  4 Basic application
  TGS4160 sensor and through the use of high input impedance, low bias current op amp to amplify, and then make some simple computing to CO2 concentration in the range of 300 ~ 5000ppm was measured signal, the signal is 0 to several hundred mV voltage signal, can be used for high precision A / D sampling used. If you are using Figaro (FIGARO) provided by AM-4 CO2 sensor modules can be directly applied to automatic ventilation system or CO2 gas monitoring. The module has an internal A / D converter, and has been sampling the data and made a deal. Its output voltage signal and a linear relationship between CO2 concentration, the output voltage signal is 0 ~ 3.0V, the equivalent of 0 ~ 3000ppm of CO2 concentration. In addition, the module also provides a relay switching control signal. When CO2 concentration was higher than the set value, the output of the switching control signal is high 5V, the signal can make the red LED light; the contrary, it will transfer control signal is low so that the green LED is lit 0V . However, the module is a sub-file setting, not continuously adjustable. Is divided into fourth gear (jumper on the circuit board can be achieved), Table 1 and Table 2 were given the concentration threshold value and switch signals jumper connection method. AM-4 module, practical circuit diagram shown in Figure 2.
  Table 1 Threshold signal levels
  Control signal threshold
  Level switch
  800ppm 720ppm
  1000ppm 900ppm
  1500ppm 1350ppm
  2000ppm 1800ppm
  Table 2 jumpers
  Connection
  Grade JP5 JP6 JP7 JP8
  Again and again with broken
  disconnected again and again
  with broken again and again
  off again and again with
  If that is not convenient to use AM-4 module or that the price is too high, you can also design their own circuits, and write your own program for processing.
  5 Conclusion
  TGS4160-type CO2 sensor is particularly suitable for continuous monitoring of CO2 in place, it does not require power, and its stability. But TGS4160 sensor is not suitable for portable or hand-held CO2 do measuring instruments. Because the warm-up time is too long, can not immediately measure, while the sensor power as well. In addition, the sensor is exposed to certain gases (such as chlorine) will reduce the sensitivity to the zeolite interference of certain gases (such as ethanol) to be filtered out. Thus, the desiccant can be placed when not in use, and use special bags were sealed.