It isn’t just ”only air” which is being used here: a significant amount of energy is required in the making of compressed air! Therefore, the demand for determining compressed air consumption, allocation and optimization of expenditure is of increasing importance.

In modern, economically operated compressed-air ductwork systems it is a normal occurrence that the direction of the flowing compressed air varies. This is synonymous with a change in the ”flow” of expenditure. If the costs of the compressed air consumption for the manufacture of certain products is not only to be allocated by highly esteemed distribution keys but also to establish a measurement of the basis of the distribution of costs, this can only be made possible by installing appropriate measuring equipment. Direction of flow and consumption must be determined and the amount of compressed air as well as the plus / minus direction registered.

At the Mercedes Benz factory in Untertürkheim the Höntzsch vane wheel flow sensors FA are used for in-house calculation of compressed air.

The principle of measurement of vane wheel flow sensors is based on the fact that a vane wheel rotates at a speed proportional to the flow velocity of the compressed air. An inductive proximity switch of which oscillator coils generate an electrostatic field, senses the direction of the vane wheel rotation. When a vane wheel tip is inserted in this electrostatic field a resonant circuit vaporizes and an impulse is generated from it. These electric impulses are supplied to the respective evaluation unit where they are, for instance, converted into a linear velocity display, strictly proportional to the impulse frequency. Further advantages are not only that soilage does not influence the impulse recognition but also the light weight of the vane wheel thereby adapting its rotational speed in millisecond range to intervening velocity changes.

By fitting a further inductive proximity switch, sensing of the direction of the vane wheel rotation and the indication of the plus / minus direction of flow is made possible.

The Mercedes Benz light metal foundry in Untertürkheim is supplied with compressed air from the network via two main pipes. In addition a compressor with a standard volume flow of approx. 6000 m³/h is installed in the building. Depending on the operating method of the compressor and on the compressed air consumption of the light metal foundry, compressed air is taken from the network or released in to the network. Höntzsch ZSR 25/30 vane wheel flow sensors are installed in the two main pipes. Evaluation units with pressure and temperature compensation ensure that the measuring result is always directly and precisely displayed as standard volume flow or standard quantity. The Höntzsch vane wheel flow sensors FA which are in use have a measuring range of +/-0.4 ... +/-20 m/s. The VTP-FAR evaluation unit has inputs for temperature, absolute pressure and the flow sensors as well as display units for the amount of compressed air in plus or minus direction respectively as well as for standard volume flow, temperature, pressure and velocity. Dependent on the direction of flow the amount of compressed air is registered in Nm³ on the ”plus metre” or ”negative metre”. The balance of the five metres permits the exact determination of the compressed air consumption in the Mercedes Benz/Untertürkheim light metal foundry.

Compressed air is under pressure of expenditure! The Höntzsch/Waiblingen direction sensing vane wheel flow sensors permit the determination of flow direction and consumption as well as the registering of amount of compressed air and plus / minus direction. In this way allocation and optimization of expenditure is made possible.