Gas mixing apparatus for automated gas sensor characterization

Abstract

We developed a computer-controlled gas mixing system that provides automated test procedures for the characterization of gas sensors. The focus is the generation of trace gases (e.g. VOCs like benzene or naphthalene) using permeation furnaces and pre-dilution of test gases. With these methods, the sensor reaction can be analyzed at very low gas concentrations in the ppb range (parts per billion) and even lower. The pre-dilution setup enables to cover a high concentration range (1:62 500) within one test procedure. Up to six test gases, humidity, oxygen content, total flow and their variation over time can be controlled via a LabVIEW-based user-interface.

Novel method for the detection of short trace gas pulses with metal oxide semiconductor gas sensors

“…We achieve a relative resolution of better than 1 % per decade (Baur et al, 2018). For the characterization of the sensors with trace gases, we use a gas mixing apparatus (GMA) with pre-dilution lines (Helwig et al, 2014). Figure 3 shows the schematic setup of the GMA.…”

“…The outputs of the two pre-dilution MFCs are connected to each other and are kept at a constant pressure by a pressure regulator. According to Helwig et al (2014), a dynamic concentration range c bootle /c sensor from 5 to 312 750 is reached, where c sensor is the concentration over the sensor and c bottle is the concentration in the test gas bottle. Diluted gas is dosed via another MFC (20 mL min −1 ) and regulated by a 3/2-way valve.…”

Highly Sensitive and Selective VOC Sensor Systems Based on Semiconductor Gas Sensors: How to?

“…As the zero air used for the test gas is different from that used in the rest of the test setup, the observed sensor response can be caused by the contamination and not by the intended target gas when standard test gases with very low concentrations are used for direct measurement at ppb-level. Suitable approaches are the use of permeation tubes to introduce the target gas directly into the (zero air) carrier gas stream or two-stage gas dilution, allowing the use of test gases with concentrations much higher than any contaminations [56]. In both cases, the gas to be tested is injected into a carrier gas stream, which still contains contaminations, but the setup, which uses the same zero air throughout the system, ensures that the concentration of all contaminants stays constant, allowing the measurement of the sensor response to a change of only the target gas concentration.…”

Development of throttle selector of significantly different pressures for gas-dynamic tools

“…У газоаналітичних системах часто використовують в одній схемі декілька ста-білізаторів, наприклад для задання різних тисків. Проте використання кількох (часто різнотипних за діапазоном стабілізованих тисків) стабілізаторів, які в силу навіть незначних конструктивних від-хилень при їх виготовленні мають різні витратні характеристики, не забезпечує однонапрямленої і пропорційної зміни тисків [9,10]. Крім того значен-ня підтримуваного тиску залежить від величини завдання тиску і значення витрати газу через ста-білізатор, отже відоме застосування стабілізаторів не завжди забезпечує підвищені вимоги до точності завдання тиску і витрати.…”

“…-отвори круглої форми [3][4][5]; -отвори конічної або тороїдальної форми [6,7]; -комірки, утворені отвором і лопаткою [8,9].…”