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Micromote
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Clear liquids such as water cannot be detected by optical means in transparent pipes or containers without further ado. It gets especially difficult if the pipe diameter is very small or if the containers are only semi-transparent.
When using optical sensors for detection of water presence, the effects of light transmission and refraction in water can interfere with one another to such an extent that measurements are actually reversed, especially in the interaction with the container walls.
To solve this problem, the miniature optosensors of the MICROmote “JJ” series were developed by STM. The transmitters work in the upper infrared range. Water shows at this point a maximum in the absorption spectrum and the light of this wavelength is absorbed by the individual molecules.
Water thus becomes “non-transparent” for the optical system and detection is drastically simplified. Depending on the size of the miniature optosensor respectively the effective diameter of the beam, level detection can be attained with particular precision.
Along with high reliability in standard applications, this measurement method demonstrates great versatility of STM’s miniature optosensors in application:
It even functions with cloudy or milky semi-transparent containers or with varying distances between transmitter and receiver.
Vapours containing water can also be reliably detected.
The water content of transparent liquids can thus also be approximately determined by means of the different attenuation.
A special advantage of the miniature “JJ” optosensors of the MICROmote family is the extremely small design. It allows space-saving integration even in places that are difficult to access. The electronic evaluation unit in a separate amplifier with a digital signal strength display nevertheless allows comfortable setting.
The sensors of this series are available either as separate emitter/receiver units with highly flexible cables, as pre-aligned precision tube sensors or as ready-to-use trough beam fork sensors with integrated electronics. Customer specific micro designs for capillaries and micro channels in micro fluidic applications are also available as special versions.
Because of the precise differentiation between liquid and air all these sensors can, with inverted logic, straightaway be used for bubble detection. Due to the precise optics and accurate beam shaping they can achieve a much higher object resolution than e.g. ultrasonic detectors. The complexity of optical detection is raised to another magnitude if the bubble dimensions get microscopically small and their size becomes smaller than the inner diameter of the tubes.
The new TSL-K optical micro bubble detector can reliably handle even such conditions. Several micro optical sensors simultaneously illuminate the liquid in different directions and thus achieve a uniform sensitivity over the entire diameter of the liquid column. With the movement of bubbles through the measurement range, the light is diffracted or scattered at their surface due to their approximately spherical shape.
The signals received from the individual sensors are evaluated with regard to their dynamic nature in the electronic amplifier unit. Each pass, even of tiny micro bubbles, gives signal peaks that can be reliably detected.
Due to the modular design, the different sensors of the “JJ” series as well as the micro bubble detector can be quickly and easily adapted in the factory to customer specific tube diameters and materials.