Description of Controlled Calibrated Constant-Pressure Device
The newly developed apparatus is a handheld instrument able to exert pressure in a controlled manner to the sealant joint. Extending from the housing at the front of the device is an armature with a roller at the tip. Behind the armature is a piston charged with compressed gas delivered from a pressurized tank. The amount of pressure behind the piston translates directly into the amount of force that is applied to a surface to which the roller probe is engaged. The amount of gas pressure delivered from the pressurized tank is adjusted with a regulator. Pressure within the device and behind the piston is monitored from a gage visible at the rear of the housing. Within the housing the gas pressure is manipulated in such a way that the pressure is constant within the entire stroke of the piston. Pressure in the apparatus as derived from the gas source resulting in strain at the probe contact point is maintained provided that the armature is somewhere within the stroke of the piston. The user pushing in or pulling from the joint with the device during operation cannot alter the pressure at the probe contact point. This means that the pressure that the test probe exerts on the sealant remains constant. To maintain constant pressure, the piston must simply be kept within its stroke range.
The bottom line is that pressure applied to the joint for the purpose of testing is not dependant on adjacent surfaces (as in the case of a backer rod placement style device) or the judgment of the user (as in the case of a screen roller or similar device) when using the pressure controlled device (see Fig. 1).
The ability to maintain consistent controlled strain coupled with infinite adjustability provides the opportunity for calibration. This was described in detail in the above referenced paper .