Pressure Calibration in Ballistics Testing

PCB Piezotronics recently hosted a two-day pressure measurement and calibration training in Depew, NY for the Sporting Arms & Manufacturer's Institute (SAAMI). This group's Technical Committee develops product standards for firearms and ammunition.  The Modal Shop also attended the training, supporting the metrology aspects of the program.

One of the topics discussed was fundamental measurement problems in ballistics. One of these issues is the fact that the transducer needs to be as close as possible to the physical event while at the same time not interfering with the measurement event. In this case, we want to measure the pressure change inside a piece of ammunition when it is fired. To put the sensor inside the brass casing is impossible. So the measurement alternative is to put it on the outside of the brass casing and measure the pressure event on the outside of the brass casing...

This is possible through the unique design of the PCB pressure sensor, and also through the pressure calibration procedure. Ballistics in-barrel pressure sensing is unique in that it measures the pressure through an extra media, namely the brass cartridge of the ammunition. Since the testing measurement is made through that brass cartridge, SAAMI users also need to calibrate their sensor through the brass cartridge. This calibration is repeated for every lot code of brass, and those characteristics need to be compensated for in the calibration. This need for high repetition calibration is addressed by automated ultra high-pressure calibration systems.

The K9905D pressure calibration system includes all the components to calibrate conformal pressure sensors (including the actuator which causes the pressure to rise), a mounting adaptor (which is designed to match the dimensions of the barrel of the weapon), and the reference sensor to measure the reference pressure.

The actuator creates a pressure rise in an oil media that is measured by the reference sensor, and this high pressure is applied to the inside of the brass cartridge. The pressure rise on the outside of the brass cartridge is measured by the Sensor Under Test. The K9905D automates this process to allow very fast collaboration. As the pressure rises, the data is automatically collected at levels standardized by SAAMI and the TMS database, which is a typical high-pressure range for PCB conformal sensors.

The K9905D and the PCB conformal sensor line is the result of a deep cooperative effort between PCB Piezotronics and the SAAMI members to develop a very consistent and very accurate method for measuring ballistics pressures in the barrel of a weapon. The Modal Shop’s role has been to develop and support integrated systems with automation software, continuing to add value to this group of customers.