ISO 8573 Quality Classes

Using ISO 8573.1 Air Quality Classes ensures that your factory will get the compressed air quality you specified. It can also be used to define the required air quality for sensors used in the compressed air network.

Solids: Up to Class 5. The after cooler and pre-filter of the compressor have taken out most harmful particles. An additional source of particles can be rust in the pipework. Using a general purpose 1 micron filter will take out any harmful parcicle

Water: See below: Up to Class 6 (non condensing), we have not seen any significant effect on our flow meters.

Oil: May result in a thin film over time. For short audits, oil does not give any problem. In permanent installations, a regular check of the sensor is reccommended. Start with checking the sensor after 6 months: if it is still clean, you can extend the interval to 1 year and so on.

Humidity Effects

Due to it’s high operating temperature, the flow sensor will keep the
surrounding air dry. This minimizes the effect of normal humidity
variations.

Variations in Dew Point

On our in-house test facility, we have investigated the effects of dew point variation between -20 and +15 degrees C (Class 3...Class 6 according tot DIN 8573-1). The VPFlowMate shows no significant change in sensitivity over this range, which covers most industrial compressed
air applications where at least a refrigerant drier is installed.

Condensation effects (droplets)

When condensation occurs, the gas temperature is close to the dew point temperature.
Example: The air coming from an air compressor has a dew point of 35 °C. The outlet temperature is around 50 °C. As soon as the temperature drops below 35 °C, the water vapour will condensate and form small droplets. Note that the thermal conductivity of water is about 25
times higher than air. Every time a water droplet hits the sensor, the amount of
heat conducted to the medium will dramatically increase. Depending on the size of the droplet, the water will evaporate or it will temporarily cover the sensor. In most cases, large spikes can be seen in the output signal. In general, high readings up to 50% have been observed with
thermal mass flow sensors.

Solutions :

1 Place the VPFlowMate behind a drier or at a point where the water is separated from the air, for
instance behind a buffer.
2 When wet air is the permanent condition, a VPFlowScope DP is the best choice.