Oil, gas & renewables
the location. In this experiment, a cotton swab was dipped in an ethanol solution and placed right in front of the SPEC sensor. Figure 3 depicts the capture of the ethanol vapor as shown in a blue curve. The green curve is the current consumption of the entire system including the microcontroller, which is 90 mA typical. However, the current consumption of the MAX40108 itself is a mere 25.5 µA at VDD = 0.9 V and TA = 25°C as shown in Figure 4.
Figure 5. Performance of the ethanol sensor as vapour was moved far away from the SPEC sensor.
Figure 4. Current consumption at various power supply voltages and over the operating temperature range.
When in idle mode, the microcontroller wakes up every 10 seconds to monitor the ethanol vapor. When the vapour is present, the microcontroller starts measuring the vapour concentration as shown in the blue curve. The red line shows the AA battery voltage at approximately 1.5 V, and the yellow line is the CE voltage. To see the effect of the ethanol sensor’s response to the vapour concentration, the cotton swab was moved farther away from the sensor. The result was captured as shown in Figure 5. As expected, the amplitude of the vapour concentration blue curve was reduced accordingly.
CO SENSOR EVALUATION
Unlike ethanol, CO is a potentially poisonous gas resulting from the incomplete combustion processes from gasoline or even a harmless candle. So, it is important that proper ventilation be implemented to ensure health and safety when conducting this CO gas experiment. In this evaluation, a candle was used to produce the CO gas in a concealed jar, and the same sensor SPEC 3SP_ Ethanol_1000 Package 110-202 was used to capture the CO gas concentration.
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Figure 6. Performance of the MAX40108 CO sensor.
Figure 6 portrays the capture of the CO gas as shown in the blue curve. The green curve is the current consumption of the entire system including the microcontroller, which is typical 90 mA. As in the ethanol evaluation, when in idle mode, the microcontroller wakes up every 10 seconds to monitor the CO gas. When the gas is detected, the microcontroller starts measuring its concentration as shown in the blue curve. The red line shows the AA battery voltage of approximately 1.5 V, and the yellow line is the CE voltage.
CONCLUSION To measure the ethanol and CO gases accurately for consumer and industrial applications, a low power, high precision
operational amplifier that operates with a power supply voltage as low as 0.9 V is needed. The MAX40108 device is specifically designed to capture and measure the commonly encountered gases such as ethanol and CO effectively as it possesses not only a low current consumption of 25.5 µA but also a tiny dimension of 1.22 mm × 0.92 mm in the 8- ball WLP package. The amplifier features a shutdown mode for saving power further, which is imperative for wearable devices, portable medical systems, and industrial internet of things (IIoT) such as pressure, flow, level, temperature, and proximity measurements.
Analog Devices
www.analog.com October 2023 Instrumentation Monthly
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