This negative pressure is balanced through the right opening of the connecting channel. The pressure equalization of the negative pressure causes a change of flow direction from the left to the right side. The entire process is then repeated on the right side.
The period of time required for pressure equalization corresponds to a special amount of gas (litre/pulse), which has passed through the GD 300/GD 500. The frequency of the pressure equalization is proportional to the flow velocity.
The changing flow through the connecting channel is detected by a platinum wire (diameter 15 μ) in the connecting channel. A constant voltage is applied to the wire, which is permanently monitored. At the moment when the pressure equalization occurs in the connecting channel, the wire is not circulated around by gas for a short time and heats up due to the current flowing through the wire. This causes a temporary rise of the resistance in the platinum wire (like a Pt100 sensor) and the voltage drop (V=R*I) increases.
This increase in voltage is detected by the integrated calculator HB 300 Ex. Using the current output the measured value is directly transferred to a superior PLC system. Using the pulse output the signal is transferred to the external Flow Computer GDR 1501.