Temperature humidity sensors

Yagi, H. and Hideaki, K. (1995) High-temperature humidity sensor using a limiting-current-type plane multi-oxygen sensor for direct firing system. Sens. Actuators B, B25 (1—3), 701—4. 

Structure of the integrated temperature humidity sensors. Top view (above) and cross sectional view at a-b (below). 

Capacitance-humidity characteristics at various temperatures of the temperature-humidity sensor. 

The digital temperature-humidity sensor SHTl 1 is used to detect the temperature and the humidity underground. The temperature and the humidity can be detected by the SHTll sensor at the same time. The operating range of the temperature is 0 tl23.8°C, the temperature accuracy... 

The water vapor content of each electrode is different, and so a water vapor concentration cell can be fabricated by using a protonic conductor as described in sect. 4, for a high-temperature humidity sensor. In this type of concentration cell, the water vapor in the ambient atmosphere is applied as a reference. No effort is necessary to establish a standard electrode. The time necessary for 90% response is less than 1 min. The water vapor pressure at the oxide electrode is higher than that on the Ag electrode. By using different electrodes, the water vapor pressure on each of them differs. 

Fig. 3. An overview of atomistic mechanisms involved in electroceramic components and the corresponding uses (a) ferroelectric domains capacitors and piezoelectrics, PTC thermistors (b) electronic conduction NTC thermistor (c) insulators and substrates (d) surface conduction humidity sensors (e) ferrimagnetic domains ferrite hard and soft magnets, magnetic tape (f) metal—semiconductor transition critical temperature NTC thermistor (g) ionic conduction gas sensors and batteries and (h) grain boundary phenomena varistors, boundary layer capacitors, PTC thermistors.

Lead sulfide is used in photoconductive cells, infrared detectors, transistors, humidity sensors in rockets, catalysts for removing mercaptans from petroleum distillates, mirror coatings to limit reflectivity, high temperature solid-film lubricants, and in blue lead pigments (82). 

Modern EMCS use a variety of sensors, including temperature, humidity, occupancy, light, pressure, air flow, indoor air quality, and electric power (normally pulses from power meters). The actuators are... 

In several cases application of various additives to the surface of a semiconductor adsorbent, specifically adsorbing or reacting with particles to be detected enables one to improve selectivity. As an example we can mention the use of hygroscopic salts to bind water in humidity sensors, the application of particles of sulfanilic acid to the surface of hhO to detect NO2 [10]. However, the high operational temperature in majority of semiconductor sensors deprives the method of specific surface additives of its general character. 

The major requirement for a reliable hydrogen sensor operation in the fuel cell environment is in 100% condensing humidity Most of the fuel cells have abundant humidity and the sensor needs to operate continuously in humid environments. In some cases, the hydrogen sensor can also be operated at very low temperatures (as low as —40°C). The fuel cells regularly have a cold start, when operated from a very low ambient temperature the sensor needs to attain ambient temperature quickly (<30 s) and continue operation well below ambient temperature before the fuel cell itself reaches the ambient temperature. 

In a modem laboratory, automatic sensors are often used to detect unwanted changes in laboratory conditions and warn laboratory staff. Basic laboratory conditions, such as temperature, humidity and particulates, can all be monitored continuously using sensors. The results can either be fed to chart recorders, or into computer-controlled laboratory management systems, which can take corrective action or sound alarms in the event of the limit for a particular condition being exceeded. 

Several new sensors will have to be introduced alongside the current ones - several types of temperature sensors, level sensors, load and weight sensors, humidity sensors etc. 

Figure 12.8-10. Schematic drawing of the prototype unit design 1 showing the locations of the temperature, humidity and total VOC sensors.

The room temperature, humidity, and air pressure differential records were checked using the calibrated sensors for three consecutive mns and found within tolerance. 

Instrumentation, such as chart recorder, temperature and humidity sensors and controllers, and chamber alarms... 

Temperature and/or humidity mapping of the chamber at the required set point is an integral part of OQ tests. Mapping includes the placement of temperature and humidity sensors at various locations within the chamber to demonstrate that the temperature and/or humidity will be consistent throughout different areas of the chamber under ideal conditions. Temperature and humidity readings should be obtained over a defined period, typically, a minimum of 24 h. 

The operating ranges of different humidity sensors. Most humidity/dew point detectors can make measurements at higher values of humidity and temperature, but are limited at low temperatures and at low concentrations. Most are also limited to a maximum operatng temperature of about 200°F (95°C). 

Conventional humidity sensors of the electric resistance variable type use hydrocarbon polyelectrolyte as a moisture sensing material. Therefore, the sensors usually have insufficient heat resistance, and cannot be used at temperatures of 60°C or more. Another problem is that they deteriorate when in contact with cigarette smoke and oil contained in the air [64,65]. When the fluorinated pitch-deposited coating was breathed upon, the electrical resistance quickly decreased, but electrical resistance quickly recovered when this action was stopped. Then, how to develop a humidity sensor excelling in humidity response sensitivity, heat resistance and durability was attempted [66]. Two kinds of comb-like electrodes with different electrode gaps were made, and a thin film was formed on the surfaces by vacuum deposition of fluorinated pitch. The obtained fluorinated pitch sensors were left at rest in a thermostatic chamber, and electrical resistance was determined under the following conditions. 

Sensor B (MOS) experienced the most cross-sensitivity, responding to temperature, humidity, CO/CO2 and propene. It also read consistently high in the presence of H2. In general, cross sensitivities appear to be linear combinations, i.e. no synergistic effects. 

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