The PTC-01P gas sensor: Safe CO2 detection in many applications

The detection of CO2 concentrations may range from low ppm levels up to 100 Vol% CO2. In practice, there are many different applications, where CO2 is being measured for safety reasons or being used in industrial processes. An example of an application, where CO2 is being used in an industrial process, but at the same time has to be measured for safety reasons, is the production of dry ice. Production of dry ice requires pressurized CO2 gases in high concentration. Workers need to be protected against any CO2 leaks, both in ppm level concentrations (long-term exposure), but also in % level concentrations (sudden leaks from pressurized process equipment). The means of protection is by measuring the CO2 gas levels in critical areas of the production using either fixed installations or portable devices. Pewatron presents the PTC-01P CO2 gas sensor which is ideally suited for measurement of gas leaks in portable devices, but also for many other gas sensing and analysis applications. 

The measurement principle of the PTC-01P sensor is a differential measurement of thermal conductivity relative to air. CO2 or other gases with a sufficiently large difference in thermal conductivity compared to air will change the measuring value of a measurement resistor more than that of a reference resistor. The PTC-01P is a MEMS sensor die in a TO housing composed of two platinum thin-film resistors. The measurement resistor is residing on a thin electrical and thermal insulation membrane suspended over an etched cavity in the silicon die. The reference resistor is residing on the bulk silicon substrate and measures the temperature of the substrate. With a constant current heating the membrane, the difference in temperature between the reference and the measurement resistor correlates with the thermal conductivity of the surrounding gas. The reference resistor is also used to compensate the dependence of the thermal conductivity on the absolute temperature.

One key feature of the PTC-01P is the ability to operate in a very wide temperature range from -40°C to +85°C, whereas best performing NDIR CO2 gas sensors can only operate in a range from -20°C to +65°C. Another key feature is the very fast response time of the sensor, which is only limited to changes in the measurement resistor, which is in the order of milliseconds. The response time of the sensor in the sensing device is thus only limited by the gas path to the sensor. The PTC-01P sensor has a very low power consumption (5 mW) and is superior to most NDIR based CO2 gas sensors in this respect too. The resolution that can be achieved with the PTC-01P is highly dependent on the conditioning electronics and the ability to measure very small differences between the reference resistor and the measurement resistor.

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