Standard cavity pressure sensors

Figure 5.12 describes the advantages of this principle. Standard cavity pressure sensors are shown in the top row where the first one is installed correctly (left) and the second one touches the sensor bore due to an inclined installation (right). As a consequence, the second sensor loses sensitivity (force shunt). This is reflected in the measured values, which are too low (shown schematically by the two internal pressure curves). The so-called PRIASAFE sensors, which are protected by a sleeve, are shown in the lower row. Both the correctly installed sensor (left), as well as the sensor with the sleeve touching the sensor bore (right), provide identical, problem-free measurement signals. This principle considerably facilitates the handling of cavity pressure sensors. 

Cavity pressure sensors are a contradiction in themselves on the one hand, they are highly sensitive measuring instruments on the other, they are in practice often treated no more respectfully than bolts, pins, or other mold standards, although a significant investment is made in them. 

Cavity size (volume) Approx. 50 L Delivered power 1500 W Max. output power 1200 W Temperature control Outside IR remote sensor Immersed fiber-optic probe (optional) Pressure measurement Pneumatic pressure sensor (optional) Cooling system Air flow through cavity 100 m3 h1 External PC Optional not required as integrated key panel is standard equipment ... 

Fig. 5.1.19 Silicon pressure sensor (left) and accelerometer (right) on the same chip, made possible by one of SensoNor s standardized sealed-cavity processes...

Often, only small series are produced, so the standard mold is often left on the injection molding machine while the mold inserts are exchanged for other small series. In these cases, the cavity pressure and cavity temperature sensors have to be automatically decoupled with the mold insert otherwise, the entire mold must be disassembled to replace the sensors. 

The flow cell was designed to make optimum use of the cavity and to monitor the temperature of the flow cell directly using an inbuilt IR sensor. To this end, a standard pressure rated glass tube (10 luL) is fitted with a custom built steel head and it was filled with sand (10 g) between two drilled porous frits. This is to minimize dispersion and effectively create a lattice of microchannels. It is charged with solvent (5 mL volume), sealed using polytetrafiuoroethylene (PTFE) washers and connected to an HPLC flow system with a backpressure regulator. 

---