To minimize flaws in enamelling this process is frequently carried out in clean rooms. Monitoring of the air resources in the clean rooms is the prerequisite for uniform manufacturing conditions and the high-quality standards. With the antistatic coating of automobile headlight lenses as practiced by Hella KG Hueck & Co, Lippstadt, Höntzsch direction sensing vane wheel flow sensors are used for optimization of production.

The lenses of the headlights are automatically conveyed out of the clean-room coating chambers. For this reason a monitoring of the air resources during the transport is necessary. The cylindrical vane wheel sensors measure the air currents which arise by passing through the clean room sluices. Thus the recognition of the forward and reverse current, even in the smallest of outlets, is made possible. The cylindrical shape of the sensors has proved to be especially advantageous as they are easy to install and take up very little space. As the enamelling process frequently involves measurements in potentially hazardous areas, flow sensors in ex-design are used.

The principle of measurement of the vane wheel flow sensors is based on the fact that a vane wheel rotates at a speed proportional to the flow velocity of the flowing air. An inductive proximity switch, the oscillation coil of which generates an electrostatic field, senses the vane wheel rotation. When a vane wheel tip is immersed in this electrostatic field an oscillating circuit vaporizes and an impulse is generated and relayed to the evaluation unit. A further inductive proximity switch which senses the vane wheel rotation and thus ensures the measurement of forward and reverse currents is installed in the direction sensing flow sensors.

The precise measuring technique of the vane wheel sensors records even minimal flow which is transmitted to the evaluation units. A direct evaluation of the read-out is made possible by an analog output or V24 output.

With the continuous and direct measurement of flow the course of manufacture at Hella KG Hueck & Co has been decisively improved.

Höntzsch Waiblingen vane wheel flow sensors: in use in clean room sluices they optimize the enamelling of headlight lenses. They are equipped with a transducer for the signal evaluation and provide non-intermittent and direct measurement of forward and reverse currents.

The headlight lenses are enamelled under clean-room conditions so that no dust particles can imapir the required brilliancy. A UV radiation additionally ensures that the enamell forms an extremely hard and resilient protective layer on the synthetic headlight lens.

Robots in air-conditioned rooms control the enamelling process and guarantee a constant high quality.