Pressure transducers were used for the first time in 50 years. They were covered by patent protection until recently, which affected the availability and prices in the market. Nowadays, they are available and produced by different manufacturers.
Principles of transducer operation are based on tensometric technique. Pressure transmission from built-in membrane flow canal takes place through closed capillary system filled with mercury, NaK or oil. The capillary is finished with a second membrane with a built-in tensometer which changes linearly electrical resistance accompanied by the pressure change. The proportional resistance change is used to make measurements. For transducers with built-in amplifiers we obtain normalised final signals (0-10 VDC, 0-20 mA or 4-20 mA).
Pressure sensors function as security devices for extruders in case of dangerous pressure excess which may lead to the extruder damage. Through border signals the extruder’s driving system may be switched off once the pre-defined pressure is exceeded. For this reason, every line, for its own security, should be equipped with at least one pressure sensor.