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| MicroChemical Systems P RODUCT D ATA S HEET MiCS - 5131 Ethanol Gas Sensor This datasheet describes the use of the MICS-5131 in breathalyzer applications. The package and the mode of operation illustrated in this document target the detection of ethanol in the human breath. Features: * * * * * * * Low heater current Wide detection range High sensitivity Fast thermal response Electro-Static Discharge protected Miniature dimensions High resistance to shocks and vibrations This Product Data Sheet accompanies MicroChemical Systems MICS-5131 sensors for ethanol. Reproduction and distribution of this document is restricted by MicroChemical Systems. The following specifications are subject to change to accommodate continuous improvement. For this and other quality MiCS products, send an e-mail to info@microchemical.com or contact MicroChemical Systems at: Rue de Porcena 15 * CH-2035 Corcelles, Switzerland * Tel: 41 (0) 32 731 0120 * Fax: 41 (0) 32 731 0124 MICS-5131 Product Data Sheet Page 1 of 5 Doc NO: 0178 Rev. B MicroChemical Systems P RODUCT D ATA S HEET Sensor Characteristics Important Precautions: Please read the following instructions carefully before using the MICS-5131 sensor described in this document to avoid erroneous readings and to prevent the device from permanent damage. * The sensor must not be wave soldered without protection or exposed to high concentrations of organic solvents, ammonia, or silicone vapors in order to avoid poisoning the sensitive layer. * Heating powers above the specified maximum rating of 120mW can destroy the sensor due to overheating. * This sensor is to be placed in a filtered package that protects it against any water or dust projection. * For any additional questions, please contact us at: apps@microchemical.com Operating Mode: The recommended mode of operation is a constant power mode. A heater power of PH = 102 mW is applied. This causes the temperature of the sensing resistor (RS) to reach about 450 C. Detection of ethanol is achieved by measuring the sensing resistor RS during operation. Measurement Circuit: Figure 2 shows the pin connections of the MICS-5131 gas sensor. A simple circuit to measure the ethanol level is proposed in Figure 3. The heating voltage VH is applied to pins 3 and 1. A load resistor RL is connected in series with RS to convert the resistance RS to a voltage VS between pins 2 and 4. RS can then be calculated by the following expression: RS = RL /(VCC - VS) VS Sensor Response: The sensor response to ethanol in air is represented in Figure 1. The sensor resistance RS is normalized to the resistance under air (R0). 1 3 RH 4 2 RS 1 Pin Number 1 2 3 4 Heater Ground Sensor Pin Heater Power Sensor Pin RS/R 0 Figure 2: Equivalent circuit (top view) of MiCS 5131. VCC Gas Sensor 32 0.1 10 100 1000 VH Ethanol [ppm] 41 VS RL GND Figure 3: Measurement circuit for ethanol detection. Figure 1: RS / R0 as a function of gas concentration at 50% RH and 25C. MICS-5131 Product Data Sheet Page 2 of 5 Doc NO: 0178 Rev. B MicroChemical Systems P RODUCT D ATA S HEET Cross Sensitivity: The following figure illustrates the MICS-5131 cross sensitivity to CH4, CO, C2H5OH and H2. 1 Temperature and Humidity dependence: Temperature and humidity also affect the resistance value of the sensor. Humidity is water (H2O) in gas phase, which reacts with the sensing layer like a reducing gas. Increasing humidity causes a decrease of the sensing resistance. As for the temperature, the effect is the same as for the humidity, i.e. decreasing resistance with increasing temperature. This negative temperature coefficient is due to the semiconductor properties of the sensing layer material. Rs / Rair [-] 10 CH4 CO Rair / Rair,25 C-50% RH [-] Rs/Ro 20% Rs/Ro 50% Rs/Ro 70% Rs/Ro 90% 0.1 10 C2H5OH H2 100 concentration [ppm] 1000 1 Fig. 4: Sensitivity to CO, H2, CH4, and C2H5OH at 25C and 50% RH. Response time: A typical response curve under laboratory conditions is shown in figure 5. The test gas is 60ppm of C2H5OH and the sensing resistance reaches 90% of its final change in about one second. 0.1 0 20 40 Temperature [ C] 60 80 Fig. 6: Temperature dependence of baseline resistance Rair for 20%, 50%, 70% and 90% RH. 1.2 1 0.8 Rs / R0 [-] 0.6 0.4 0.2 0 -10 -5 0 time [second] 5 10 Fig. 5: Response time to 60ppm C2H5OH MICS-5131 Product Data Sheet Page 3 of 5 Doc NO: 0178 Rev. B MicroChemical Systems P RODUCT D ATA S HEET Electrical Specifications Maximum Ratings: Rating Maximum Sensor Supply Voltage Maximum Heater Power Dissipation Maximum Sensor Power Dissipation Relative Humidity Range Ambient Operating Temperature Storage Temperature Range Storage Humidity Range Table 1 Symbol VCC PH PS RH Tamb Tsto RHsto 5 -40 -40 5 Value / Range 5 120 1 - - - - 95 120 120 95 Unit V mW mW %RH C C %RH Operating Conditions: Parameter Heating Power, [1] Heating Voltage, Heating Current, Heating Resistance, [2] Table 2 [1] Symbol PH VH IH RH Typ 102 3.2 32 100 Min 85 90 Max 120 110 Unit mW V mA A minimum value of 85mW ensures sufficient sensitivity to ethanol. Heating powers above 120mW can cause permanent damage to the sensor when ambient temperatures exceed 120C. Heating resistor values from sensors out of production range between 90 and 110 Ohm. Due to material properties of the heating resistor its value increases during operating life. This behavior has to be taken into account in the application design. [2] Sensitivity Characteristics: Characteristic Ethanol Detection Range Sensing Resistance in air Sensitivity Factor [4] Table 3 [3] [4] [3] Symbol FS R0 SR Typ 24 1.4 Min 10 18 1.3 Max 1000 180 1.8 Unit ppm k - Sensing Resistance in air R0 is measured under controlled ambient conditions, i.e. synthetic air at 232C and 505 %RH. Sensitivity Factor SR is defined as RS at 60ppm of CO divided by RS at 200ppm of CO. Test conditions are 505 %RH and 232 C. MICS-5131 Product Data Sheet Page 4 of 5 Doc NO: 0178 Rev. B MicroChemical Systems P RODUCT D ATA S HEET Package Dimensions and Filter J A B C H I K D E Dimension A B C D E Min [mm] 9 8.15 5.75 0.6 3.5 9.0 12.5 2.41 0.55 4.83 0.7 Max [mm] 9.15 8.30 5.85 0.9 3.9 10.0 13.9 2.67 0.65 5.33 0.9 G F F G H I J K MICS-5131 Product Data Sheet Page 5 of 5 Doc NO: 0178 Rev. B |
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