The model OLS optoelectronic level switch is used for the detection of limit levels in liquids. This is widely independent of physical characteristics such as refractive index, colour, density, dielectric constant and conductivity. Measurement is also done in small volumes.

The switches consist of an infrared LED and a phototransistor.
The light of the LED is directed into a prism. So long as the
sensor tip of the prism is in the gas phase, the light is reflected
within the prism to the receiver. When the liquid in the vessel
rises and wets approximately 2/3 of the glass tip, the infrared
lightbeam into the liquid is interrupted and only a small portion
reaches the receiver. This difference is evaluated by the
electronics and triggers a switching operation.

The instruments are very robust and designed for rough operating conditions.

The cable to the switching amplifier does not need any shield, enabling easy and economic cabling. The model OSA-S switching amplifier is operated with an intrinsically safe signal circuit. For the 19″ plug-in card version, all operating elements, except for the switch for changing the alarm direction and the potentiometers for the time delay, can be accessed from the front. If incorporated in an add-on case, a transparent cover allows seeing the switching statuses.