Measuring Gas Velocity with the D-FL 100 Differential Pressure Bar

D−FL 100 Seite 83.2. Differential Pressure TransducerThe differential pressure is measured using the differential pressure transducer. Fig. 7 is a diagram of atransducer.The differential pressure is transmitted, via separating membranes and a filling liquid, to a siliciumpressure sensor. If the measuring limits are exceeded, the overload membrane expands until one of theseparating membranes attaches itself to the pressure sensor and thereby protects the silicon sensorfrom overloads.The applied differential pressure expands the measuring membrane laterally. Consequently, the piezoresistors, which are switched in a jumper array and integrated into the measuring membrane, changetheir respective resistive load value. This change in resistor load leads to a jumper output voltage whichis proportional to the differential pressure. This signal is transformed into an output current of 4 to 20mA.Fig. 7:Diagram of a differential pressure transducerThe range of the differential pressure transducer can be adjusted to anywhere from 1 to 20 mbar. Theseparating membranes inside the transducer can be made of either stainless steel (material No. 1.4404)or Hastelloy C276 (material No. 2.4819).The differential pressure transducer comes with an installation bracket and a switching valve mounteddirectly on the transducer. The switching valve permits cleaning of the differential pressure bar withcompressed air, thereby lengthening its maintenance cycle. The zero point check of the differentialpressure transducer can also be performed with the switching valve.The transducer must always be installed above the differential pressure bar. At least the first part of thesupply line from the differential pressure bar should be installed at a slight incline toward the differentialpressure transducer, so that condensation can flow back to the bar in this area.When the ambient temperature is lower than the gas temperature, condensation buildup -- especiallyinside the supply lines to the differential pressure transducer -- will alter the measurement considerably.GmbH