We once took air-conditioning for granted, but the incidence of Legionnaire’s disease has concentrated attention on the problems that can arise if air-conditioning is fitted and forgotten. In addition, there is an energy wastage aspect to consider when air-conditioning is run continuously, and the problem of the noise which, even at a low level, is … Continue reading
Moisture
The presence of moisture in gases or solids often needs to be sensed or measured. A high moisture content in a gas (high humidity) will cause condensation when the gas is cooled, and this can have the effect of depositing liquid in pipes, causing blockages. Conversely, a gas whose humidity is very low can absorb … Continue reading
Water Purity
There is no single instrument that can assess all aspects of water purity, because this would require the assessment of both ionizing and non-ionizing contaminants, bacterial and viral presence, dissolved gases, color and taste; hardly a task for which any one instrument is suited. One reading that can be a very useful guide, however, is … Continue reading
Moisture in Solids
Moisture in solids can be sensed in terms either of the conductivity of the materials, changes in permittivity, or of the absorption of microwaves. For sensing the presence of moisture in materials of comparatively fixed composition (even where some variation occurs, as in masonry), a simple resistance reading between connectors set at a fixed distance … Continue reading
Animal fat thickness
One of the more specialized uses of sonar distance meters has been in measuring the thickness of the layer of fat under the skin of animals, pigs in particular. The speed of sound in a fatty layer is different from the speed in the more dense meat; so that an ultrasonic beam will be reflected … Continue reading
Wind Chill
The effect of wind on heat-loss has been known for a long time, but wind-chill factors have only recently been quoted in weather forecasts to the general public.The principle is that an object located in still air will lose heat comparatively slowly, because the air itself acts as a thermal insulator. Even for a comparatively … Continue reading
Acidity/alkalinity
The acidity or alkalinity of water is an important factor for water suppliers and also for all users of water such as chemical plants, generating stations, agriculture and horticulture. The acidity or alkalinity of water is measured on the pH scale, on which perfectly neutral water has a pH value of 7, fairly strong acid … Continue reading
Time
The measurement of time is fundamental to many industrial processes as well as to civilized life in general, but it is only comparatively recently that electronic timekeeping has become important. Our units of time are based on the solar year, the average time that the Earth takes for one revolution around the Sun, which is … Continue reading
Viscosity
The viscosity of a liquid or gas is the quantity that corresponds to friction between solids, and which determines how much pressure will be needed to drive the liquid or gas through a pipe. In addition, some chemical reactions result in very marked changes in viscosity, so that sensing methods are needed for liquids that … Continue reading
Gases
The velocity of gases can be measured in the same ways as are used for liquids, but a few specialized methods are added. Figure 1 The rotating cup sensor for wind velocity. The rotating arms can be mounted on the shaft of a tachogenerator or synchro for a direct electrical output.
Sensors and Transducers 