We cannot imagine today's world of industrial production without compressed air as a source of energy. Because of the high costs in manufacturing, it is important that it is used effectively, as compressed air tools and other consumers can only function at their best if used in accordance with the standards regarding to flow rate and air pressure. However, this is only possible if the required level of knowledge of airflow and pressure exists at all relevant points in the network.

A single measurement of these two values taken at the compressor station is, especially in the case of extensive networks, not sufficient. That is because, amongst other things, between compressed air manufacturer and consumer, leakages occur which must be taken into consideration when contemplating the costs. Much energy and tool power is also wasted at any type of connecting point, as this results in a very high pressure drop if attention is not paid to a clean cut passage in the planning or retrofitting. Leakages are a further cause of air waste. For example, the prime cost of leakage from a hole with a diameter of 5 mm amounts to the equivalent value of compressed air of approx. 20,000 German Marks! Even in the case of well-maintained compressed air networks, an air loss of 10 percent must be reckoned with.

Moreover, for the quantity measurement of compressed air consumption in larger networks there is every indication that dealing with energy is done with a greater awareness, the more precise the consumer costs can be assigned to the individual resources.

Within the framework of the energy management observations on the acquisition of cost flows and the establishment of a compressed air demand profile, a major car manufacturer in Southern Germany has decided to use thermal flow sensors manufactured by Höntzsch GmbH / Waiblingen for measuring compressed air consumption in the power supply in individual workshop halls.

Interestingly enough, additional pressure measurement for determining air mass flow is no longer necessary. A further great advantage is that moving sensor parts have been dispensed of, resulting in a high degree of robustness. Consequently, the sensor system keeps the operational and maintenance rates low, furthermore also optimising the reliability of the system and guaranteeing continuous, trouble-free operation.

For equipping the measuring points, TA insertion sensors were used for installation in pipelines of Di 100 mm and Di 150 mm These were attached to the pipelines using probe guide pieces. For measuring in the compressed air piping Di 50 mm, TA-Di 50 sensors in wafer-type construction were installed.

The processing of the sensor signals is carried out by microprocessor-controlled evaluation units, which supply the current signals on the output side proportional to flow. These and additional quantity counts were sent to the central control room, in which two computer units redundantly control all process parameters. Due to the improved evaluation of the temporal and spatial distribution of the compressed air consumption or loss, the investment for the compressed air quantity measurement pays for itself within a very short time.