Miniature Cavity Pressure Sensors – The Next Generation 

By Christopherus Bader, CEO, Priamus System Technologies AG 

Cavity pressure sensors are the basis for mold setup, process monitoring and process control in injection molding. Very often, however, the body dimensions of the standard types available are just too big to fit into the desired locations. 

Very small cavity pressure sensors could solve this problem, but they are difficult to install due to the required accuracy of the bore dimensions. Sensor side load and a loss of sensitivity can occur if sensors are not located or positioned well in the bores. This results in compromised measuring signal accuracy. 

Miniature cavity pressure sensors such as the PRIASAFE^TM series from Priamus can help achieve better, more accurate results. These very small sensors are protected by a miniature housing and calibrated only after they have been assembled. They also protect the sensor from side load sensitivity loss effects which are entirely eliminated. Sensor installation of very small sensors is therefore much simpler than it used to be, and so are the requirements for the accuracy of the bore dimensions.   

A hardware code located within the sensor provides all sensitivity information. The electronics (amplifiers) automatically adjust the measuring range after the sensor identifies itself.  

With miniature pressure sensors, the sensor length is considerably shorter than the standard sensors offered in the market.  Their compactness makes them not only easier to install but also increases the safety factor. 

New developments in cavity temperature measurement

Cavity temperature measurement has been very often overlooked in the past. Only in the past few years, new applications based on flow front location, like automatic balancing of hot runner molds or the automatic switchover to holding pressure, have demonstrated how effective cavity temperature can be used for quality assurance in injection molding.

Priamus cavity temperature sensors have been especially developed to meet high technical performance requirements: robust handling, extreme fast reaction times and high amplitudes of the measuring signal.  Even with a very small body design, the sensor front can be machined or contoured for the best fit. 

Standard thermocouples are usually only calibrated statically. However, due to the fast reaction times when the plastic melt hits the sensor, it is much more important to determine the dynamic behaviour of the sensor. 

Priamus cavity temperature sensors are the only sensors of this kind which are calibrated dynamically after manufacturing. They are tested both regarding reaction time and amplitude and come with a serial number. 

Cavity temperature and cavity pressure sensors should be installed at different locations in the mold cavity. For process optimizing, a cavity pressure sensor needs to be located near the gate. For melt front control, a cavity temperature sensor needs to be located near the end of the flow path. A combined cavity pressure and temperature sensor should be avoided because a large sensor body leads to slower signals with small amplitudes.  

The very small, robust and very fast cavity temperature sensors are comparably inexpensive and can be easily replaced or repaired in case of broken cables.  

Easy installation with quick disconnects 

Many molded parts are not made in the mold platen itself but within mold inserts. This makes it easier to manufacture and maintain the cavities. 

Cavity pressure and cavity temperature sensors can very often not be used due to limited space. It is cumbersome to handle fixed sensor installations when mounting and dismounting the mold inserts. 

Priamus quick disconnects for cavity pressure and cavity temperature, mold inserts can be mounted and dismounted by a simple plug connection while the sensors remain in the mold insert. 

This application is especially fail-safe because the sensors do not stay in the mold platen as a "bolt" and can therefore not be damaged. They stay safely packed in the mold insert even after dismounting. 

The essential advantage of these systems is that different mold inserts with different sensor positions can be used without changing the position of the quick disconnects. Unlike a sensor which is installed in the mold platen itself, the sensor position can still be flexibly selected according to the design of the molded part. 

Cavity pressure sensors have long ago proven their value in the injection molding process. Only recently, however, have manufacturers made efforts to simplify the handling and to ensure that measuring signals were accurate and repeatable. 

Cavity temperature sensors, on the other hand, started to play an important role in the injection molding process only a few years ago. But their usage, especially when it comes to control applications, is becoming more and more significant. Required are sufficient fast response times of the sensors and an intelligent electronic so that the measured increase in temperature can also be used as a control signal. 

PRIAMUS is a global leader in cavity pressure and cavity temperature technology. 

PRIAMUS SYSTEM TECHNOLOGIES, LLC
3061 Nationwide Parkway
Brunswick, OH 44212 / USA
Phone 877 774-2687
www.priamus.com

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