Abstract: A gas sensor which works according to the principle of thermal conductivity is functionally tested. In the method, a calibration cycle is conducted in which a membrane of the gas sensor is immersed in a fluid calibration medium having a known concentration of a target gas. After the calibration cycle, a measurement chamber of the gas sensor is purged with a purging gas. Then, a measuring cycle is conducted, using a thermal conductivity sensor to measure the target gas in the measurement chamber. Using a calibration baseline established from the calibration cycle and a measurement baseline in the measurement cycle, a baseline comparison value is obtained and compared to a predetermined baseline threshold value. An error message, indicating a malfunction in the purging gas supply, is generated when the baseline comparison value exceeds the predetermined baseline threshold value.

Abstract: A gas sensor which works according to the principle of thermal conductivity is functionally tested. In the method, a calibration cycle is conducted in which a membrane of the gas sensor is immersed in a fluid calibration medium having a known concentration of a target gas. After the calibration cycle, a measurement chamber of the gas sensor is purged with a purging gas. Then, a measuring cycle is conducted, using a thermal conductivity sensor to measure the target gas in the measurement chamber. Using a calibration baseline established from the calibration cycle and a measurement baseline in the measurement cycle, a baseline comparison value is obtained and compared to a predetermined baseline threshold value. An error message, indicating a malfunction in the purging gas supply, is generated when the baseline comparison value exceeds the predetermined baseline threshold value.

Abstract: A device for applying adhesive to a substrate from a liquid container containing the adhesive contains at least one pressure tank that can be temporarily connected to the pressure tank by means of a changeover valve in order to apply a pressure pulse to the liquid container, and a control unit for controlling the changeover valve and regulating the pressure prevailing in the pressure tank. In accordance with the invention, the device is equipped with a sensor the output signal of which indicates the liquid level of the liquid container. The sensor comprises a sound transducer, a sound transformer and an electronic circuit for operation of the sound transducer and for analyzing the signal delivered by the sound transformer. The sensor measures the frequency of the alternating electrical signal applied to the sound transducer with which a standing sound wave occurs in the liquid container.